Symposium Organizers
Juergen Fassbender Institute of Ion Beam Physics and Materials Research
John Chapman University of Glasgow
Caroline A. Ross Massachusetts Institute of Technology
P1/O8: Joint Session: Patterned Films
Session Chairs
Wednesday PM, November 29, 2006
Room 310 (Hynes)
9:30 AM - **P1.1/O8.1
Magnetic Films on Self-assembled Nanoparticles.
Manfred Albrecht 1 , Till Ulbrich 1 , Ildico Guhr 1 , Olav Hellwig 2 , Sebastiaan Van Dijken 3 , Thomas Schrefl 4
1 , University of Konstanz, Konstanz Germany, 2 Hitachi San Jose Research Center, HGST, San Jose, California, United States, 3 , Trinity College Nanoscience Lab., Dublin Ireland, 4 , University of Sheffield, Sheffield United Kingdom
Show AbstractIn modern magnetic recording materials the ‘superparamagnetic effect’ has become increasingly important as new magnetic hard disk drive products are designed for higher storage densities [1]. In this regard, nanoparticle media [2], where two-dimensional arrays of monodisperse nanoparticles with high magnetic anisotropy are used, is assumed to be the ideal future magnetic recording material. In this presentation a novel magnetic gradient nanomaterial, which has been created by depositing Co/Pd multilayers onto two-dimensional arrays of self-assembled nanoparticles [3] will be introduced. The magnetic nanostructures formed on top of the particles are in a magnetically exchange-isolated quasi-single-domain state. This nanoscale system is quite distinct from the classical geometries: Neither extrinsic properties nor the intrinsic properties are uniform in space. The film is extended over a wide region of the sphere and thus shows substantial curvature. The film thickness varies and so do the intrinsic magnetic properties most notable the magneto-crystalline anisotropy, which is a key factor affecting the fundamental nature of the reversal process. The specific magnetic characteristics of such a gradient nanomaterial and in particular its impact on the reversal mechanism will be discussed. Angle-dependent reversal studies were performed for different particle sizes and the experimental results were interpreted using micromagnetic simulations [4]. Moreover, these nanoscale magnetic patterns are used to study the scaling behavior of the exchange bias effect employing antiferromagnetic layers of IrMn and CoO, offering new opportunities in the functionalization of magnetic nanostructures.[1] A. Moser et al., J. Phys. D: Appl. Phys. 35, (2002) R157.[2] S. Sun et al., Science 87, (2000) 1989.[3] M. Albrecht et al., Nature Mater. 4, (2005) 203.[4] T. Ulbrich et al., Phys. Rev. Lett. 96, (2006) 077202.
10:00 AM - **P1.2/O8.2
Magnetic And Structural Roughness In A Multilayer PatternedUsing Self-Assembled Spheres
Sean Langridge 1 , Timothy Charlton 1 , Lisa Michez 2 , Mannan Ali 2 , Christopher Marrows 2 , Bryan Hickey 2 , Ernie Hill 3 , Mike Toohey 3 , Sam McFadzean 4 , John Chapman 4
1 ISIS, Rutherford Appleton Laboratory, Didcot United Kingdom, 2 School of Physics and Astronomy, University of Leeds, Leeds United Kingdom, 3 Department of Computer Science, University of Manchester, Manchester United Kingdom, 4 Department of Physics and Astronomy, University of Glasgow, Glasgow United Kingdom
Show AbstractThe functionality of magnetic multilayers is derived from their interfaces, which may exhibit both structural and magnetic roughness. We have prepared antiferromagnetically coupledCo/Ru multilayers on a nanoscale patterned substrate to study the influence of a controlledsurface morphology on the relationship between these two forms of disorder. The patterningwas realised through nanosphere lithography to prepare a template onto which the magneticmultilayers were deposited, and the internal magnetic microstructure was probed using offspecular neutron reflectometry. Here we show that a quantitative analysis reveals that thepatterning induces a concomitant magnetic roughening of the system which is not observed in the unpatterned system. The results are confirmed by micromagnetic simulation. This effectis particularly prominent for the exposed surface structures. Significantly, the magneticordering is controlled by the structural morphology throughout the entire thickness of thestructure. For the optimisation and understanding of the next generation of spin-electronicdevices, exchange biassed systems and particularly patterned systems, that rely on interfacialmagnetism then measurements such as those presented, which are able to probe inter and intralayer ordering and separate bulk from interfacial phenomena from buried interfaces are particularly useful and extend the information attainable through more conventional magnetometerytechniques.
10:30 AM - P1.3/O8.3
Magnetic Nanostructures by Laser Manipulation of Atoms.
Grzegorz Myszkiewicz 1 , Erich Jurdik 1 , Fred Atoneche 1 , Tonnie Toonen 1 , Albert van Etteger 1 , Theo Rasing 1
1 , Institute for Molecules and Materials/Radboud University Nijmegen, Nijmegen Netherlands
Show AbstractWe present a novel way of fabricating periodic structures with areal densities of 1 Tbit/inch2 and possibly beyond. A big advantage of the employed technique – laser-focused deposition – is its extreme parallelism combined with very high accuracy, which allow growing nanostructures on macroscopic sample areas (~mm2). In our experiments we have focused iron atoms and subsequently grown them into nanolines. The nanoscopically corrugated iron surface consists of highly-uniform nanolines with a period of 186 nm, a full-width at half maximum of 95 nm and a height (above the background) of 8 nm. The magnetic measurements performed on the fabricated sample – magnetic force microscopy and magneto-optical Kerr measurements – both revealed a ferromagnetic behavior with in-plane easy axis that was independent from the position on the iron patch (irrespective of the presence of nanolines). This is due to a large background layer of about 25 nm. This drawback could be overcome by nanofabrication of magnetic materials with periodically varying composition and thus magnetic properties. This can be achieved by selective manipulation of iron during simultaneous deposition of a number of other species. In our recent laser-focused experiments with chromium atoms we achieved the extremely high resolution of 16 nm, which, when transferred to magnetic materials, might lead to practical applications (in, for example, magnetic data storage devices). Although there exist other techniques for nanofabrication on a similar scale, like electron beam lithography and self-assembly, the advantage of our method is that it can cover macroscopic surface areas within a single deposition run and, at the same time, maintain the extreme periodicity of the pattern. To the best of our knowledge, no other technique has been able to demonstrate such a result so far and this, in its very spirit simple experimental concept, can potentially have a large impact on industrial developments. The patterned media concept is currently considered as the most promising alternative that will help to overcome the superparamagnetic limit of the magnetic storage technology and thus help the industry to move forward. It is very possible that the technique of laser-focused deposition will enable a new generation of magnetic storage devices. Part of this work was supported by the Dutch nanotechnology R&D initiative NanoNed and the Stichting voor Fundamenteel Onderzoek der Materie (FOM), which is financially supported by the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO).
10:45 AM - P1.4/O8.4
Ripple Induced Modifications of Magnetic Properties.
Maciej Oskar Liedke 1 , Adrian Keller 1 , Stefan Facsko 1 , Jurgen Fassbender 1
1 Institute of Ion Beam Physics and Materials Research, Forschungszentrum Rossendorf, Dresden Germany
Show AbstractSelf-organized ripple formation during ion erosion of a Si wafer is used to create a template system with a well defined roughness of uniaxial symmetry. By using special buffer layers subsequent thin magnetic film deposition by molecular beam epitaxy leads to a periodically modulated magnetic thin film with drastically modified magnetic properties with respect to a nominally “flat” film of the same thickness. In the case of Permalloy thin films, an enhancement of the uniaxial in-plane anisotropy by approximately a factor of 20 is observed. The enhancement can be explained by a combination of step induced dipolar and magnetocrystalline surface anisotropy contributions. If a ferromagnet/antiferromagnet-bilayer is deposited a superposition of ripple-induced uniaxial anisotropy and exchange coupling induced unidirectional anisotropy is observed. Since the direction of the unidirectional anisotropy depends only on the magnetic field direction during a field cooling procedure any angle between both anisotropy contributions can be set. The observed angular dependence of the magnetization reversal behavior is in perfect agreement with simulations based on the Stoner-Wolfarth coherent rotation model.
11:30 AM - P1.5/O8.5
Patterned Magnetic Nanostructures by Partial Crystallization of Amorphous Alloys on Patterned Catalytic Nanoparticles.
Anup Gangopadhyay 1 3 , Christopher Favazza 1 3 , Lydia Longstreth 1 3 , Clayton Miller 2 , Ronald Indeck 2 3 , Ramki Kalyanaraman 1 3
1 Dept. of Physics, Washington University, St. Louis, Missouri, United States, 3 Center for materials innovation, Washington University, St. Louis, Missouri, United States, 2 Dept. of Electrical and Systems Engineering, Washington University, St. Louis, Missouri, United States
Show AbstractBecause of potential applications in data storage and sensor development, any efficient processing method that can produce a regular array of ferromagnetic nanocrystals is interesting. Here we demonstrate a cost-effective bottom-up processing method that can produce one (1-D) or two dimensional (2-D) Fe-based nanocrystal arrays by partial crystallization of amorphous alloys. The method involves: a) formation of patterned arrays of catalytic nanoparticles (Cu, in the present case) by laser-induced self-assembly; b) deposition of a Fe-Si-B-Nb amorphous alloy on this Cu array by laser ablation; and c) partial crystallization of the amorphous alloy by heat treatment to produce Fe-Si nanocrystals on top of the Cu nanoparticles by heterogeneous nucleation and growth. The diameter, height, and separation of the ferromagnetic nanocrystals, and therefore, their magnetic properties can be controlled. Although demonstrated for a specific system, the method can be applied to a wide variety of materials by using material-specific catalytic nanoparticles, and by exploiting the much wider solubility of elements in the amorphous phase.
P2/O9: Joint Session: Magnetic Nanostructures
Session Chairs
Wednesday PM, November 29, 2006
Room 310 (Hynes)
11:45 AM - P2.1/O9.1
Tailoring Ordered and Oriented Inorganic Nanostructures with Molecular-Templated Processing
Michael Hu 1
1 , Oak Ridge National Laboratory, Knoxville, Tennessee, United States
Show AbstractMolecular templating using block-copolymers, in combination with sol-gel chemistry and processing, could become a powerful scalable, bottom-up approach for chemical manufacturing of diversified organic-inorganic hybrids and nanoporous/mesoporous nanomaterials. However, the production of self-assembled nanostructures is usually limited in achievable sizes of ordered domains and a lack of control in nanopore orientation. This paper will present new paradigms of “engineering nanoprocesses” for controlled production of new material nanostructures having desired pore size and orientation by applying process engineering and molecular engineering principles into several sol-gel synthesis processes. With the achievement of engineered chemical processing of materials at nanoscale, we have created new nanoscale materials, i.e., inorganic membranes and nanowires that contain high ordered arrays of oriented nanoporous channels. Some potential impacts of array-based nanomaterials on applications (e.g., fuel cells, solar cells, gas separations, catalysis, electronics, sensors/detectors) will be discussed.
12:00 PM - P2.2/O9.2
Arrays of Ultrasmall, Small Symmetric and Asymmetric Nanoscopic Ferromagnetic Rings
Deepak Singh 1 , Robert Krotkov 1 , Hongqi Xiang 2 , Thomas Russell 2 , Mark Tuominen 1
1 Physics, University of Massachusetts, Amherst, Amherst, Massachusetts, United States, 2 Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts, United States
Show AbstractThere has been a considerable amount of recent interest in the magnetic properties of nanoscopic ferromagnetic rings. This is largely motivated by the unique stability of the vortex state of magnetization and its relevance in future data storage elements. In this work, we discuss experimental research on ultra-small, small symmetric and asymmetric cobalt nanorings. We fabricate arrays of nanoscopic rings using the techniques involving self-assembled diblock copolymer templates, electron-beam lithography, glancing angle evaporation and ion beam etching. The nanoscopic rings have an outer diameter of 13 nm and inner diameter of 5 nm in the case of ultra-small rings, whereas the small rings have an outer diameter of 150 nm and a wall width that varies from 5 nm to 30 nm. The magnetization properties of these arrays are measured in both parallel and perpendicular field orientations in SQUID magnetometer. We compare these measurements to analytical calculations for different magnetic configurations that take into account the competition between exchange energy, Zeeman energy and magnetostatic energy. Based on analytical calculations and magnetic measurements we find that for the ultrasmall ring structures, only two states are important: single domain states and flux-closure vortex states, depending upon the exchange length for the polycrystalline Co materials used. We have also shown that by creating asymmetry in the ring’s width, one can control the direction of magnetic vortex circulation that is in agreement with the prior research results. Low temperature magnetic measurements for asymmetric ring arrays exhibit interesting exchange bias effects. This work is supported by NSF grants DMR-0306951 and DMI-0531171.
12:15 PM - P2.3/O9.3
Control of the Vortex Chirality in Ring-shaped Magnetic Memory Elements Using Exchange Bias.
Wonjoon Jung 1 , F. Castaño 1 , C. Ross 1
1 DMSE, M.I.T., Cambridge, Massachusetts, United States
Show AbstractThin film magnetic rings have attracted a great deal of attention since the ring shape could be an alternative geometry for high-density magnetic storage elements. Ring magnets can support flux-closure or ‘vortex’ states in which magnetization is oriented tangentially and no stray field exists. Data bits can be stored using the chirality of the vortex (clockwise or counterclockwise) and the absence of stray fields in these states allows for increasing storage densities since memory cells can be arranged in close proximity while maintaining magnetostatic interactions negligible. Control of the vortex chirality in ring elements is of importance for applications in magnetic data storage. Most work on the chirality control has been done with geometrical modification such as introducing a notch or flat edge to the ring. In this contribution we demonstrate the control of the chirality using exchange bias, which is a crucial element in the operation of spin valve and magnetic tunnel junction structures.Arrays of elliptical rings with a 3.2/2.0 μm major/minor diameter and widths of 400–500 nm were fabricated with e-beam lithography and lift-off processing. Co (12 nm) and Co (12 nm)/IrMn (5 nm) exchange bias structures were deposited using ion beam or dc-magnetron sputtering. Formation of the vortex state typically occurs as one of the domain walls of the bi-domain or ‘onion’ state, which is attained after saturation, unpins, moves, and finally annihilates the other wall in a reverse field. Therefore the chirality is determined by the direction of domain wall motion during the onion-to-vortex transition. We present a model that analytically describes the onion state domain wall motion in an elliptical ring in a field at an angle α with respect to the major axis. The model allows the change in energy of the system to be calculated as a wall moves from its remanent position, so that the direction of wall motion, e.g. the chirality of the vortex, can be predicted. The calculations show that for single-layer elliptical rings the chirality will be counterclockwise if a reverse field is applied at angle α between 0° and 90°, and clockwise at α between 0° and -90°, that is, the critical field direction αc= 0° (the major axis). Meanwhile, for exchange-biased rings, αc approaches the exchange bias direction β as β deviates from 0°. This prediction was compared with experimental observations of the direction of wall motion by means of magnetic force microcopy (MFM). MFM measurements showed a good agreement with the model. Based on a series of calculations and observations for various angles α and β, a phase diagram of the vortex chirality was determined. This work demonstrates that the desired vortex chirality can be obtained using an appropriate combination of field and exchange bias direction. Vortex states in the free and pinned layer of ring-shaped spin valve structures, which were investigated by magnetotransport measurements, will be discussed.
12:30 PM - P2.4/O9.4
Current-induced Domain Wall Motion in Bar-shaped Pseudo-Spin-Valve Elements.
Irenee Colin 1 , D. Morecroft 1 , F. Castano 1 , C. Ross 1
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show Abstract12:45 PM - P2.5/O9.5
Fabrication of Ring-shaped Magnetic Nanostructures for MRAM using Electron Beam and Focused Ion Beam Exposure of HSQ.
Chen Chen 1 , Michael Cabral 1 , Lloyd Harriott 1 , Robert Hull 2 1
1 Electricla and Computer Engineering, University of Virginia, Charlottesville, Virginia, United States, 2 Material science and engineering, University of Virginia, Charlottesville, Virginia, United States
Show AbstractP3: Spintronic Nanostructures
Session Chairs
Wednesday PM, November 29, 2006
Room 309 (Hynes)
2:30 PM - **P3.1
Spin-Dependent Single Electron Tunneling and Spin Accumulation in Metallic Nanoparticles.
Koki Takanashi 1 2 , Kay Yakushiji 1 2 , Franck Ernult 1 2 , Seiji Mitani 1 2
1 Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan, 2 CREST, Japan Science and Technology Agency, Kawaguchi Japan
Show AbstractTunnel magnetoresistance (TMR) has attracted much attention in recent years because of potential applications for magnetic random access memories (MRAMs) and various spin-electronic devices. A lot of studies have been devoted to magnetic tunnel junctions (MTJs) with layered structure consisting of ferromagnetic metal/insulator/ferromagnetic metal. If the size of MTJ is so small that the electrical charging energy overcomes thermal fluctuation, single electron tunneling (SET) phenomena represented by Coulomb blockade and Coulomb staircase are expected to appear. In previous papers[1,2], we reported the enhancement and oscillation of TMR due to spin dependent SET, using device structures consisting of a microfabricated Co-Al-O granular film between two nonmagnetic or ferromagnetic electrodes. Recently, we have found that the spin accumulation in Co nanoparticles plays a significant role on the oscillatory behavior of TMR with its sign change[3]. In this paper, we review the recent developments of our study on spin dependent SET using self-assembled metallic nanoparticles.In order to prepare a device structure with metallic nanoparticles, electron beam lighography technique was used for microfabrication. A typical sample was a 0.4x0.4 μm2 pillar structure consisting of Al electrode/Al-O, 2 nm/Co-Al-O granular film, 15 nm/Co electrode prepared on a thermally oxidized Si substrate. TMR was measured for current-perpendicular-to-plane (CPP) geometry. It has been found that TMR as a function of bias voltage shows oscillatory behavior associated with Coulomb staircase, and the sign of TMR changes, in other words, inverse TMR appears periodically around the steps of the Coulomb staircase. The result has been compared precisely to the orthodox theory calculation, indicating that the TMR oscillation with the sign change is caused by the spin accumulation in Co nanoparticles. The spin relaxation time in Co nanoparticles has been evaluated from the fit of the calculation to the experiment, to be approximately 150 nsec, which shows a remarkable enhancement compared to that in bulk Co (~10 psec). Possible reasons for the enhancement will be discussed.Furthermore, a device structure consisting of non-magnetic (Au) nanoparticles between two magnetic (FeCo) electrodes separated by an Al-O tunnel barrier was also prepared. A resistance change was clearly observed with the change in the magnetization alignment of FeCo electrodes, showing anomalous bias voltage dependence. This suggests the appearance of TMR induced by spin accumulation in Au nanoparticles.[1] K. Yakushiji et al., Appl. Phys. Lett. 78 (2001) 515.[2] K. Yakushiji et al., J. Appl. Phys. 91 (2002) 7038.[3] K. Yakushiji et al., Nature Materials, 4 (2005) 57.
3:00 PM - **P3.2
Manipulation of Domain Wall in Nanostructures with Perpendicular Anisotropy Driven by a Spin-polarized Current.
Dafine Ravelosona 1 3 , Stephane Mangin 2 3 , Yann Lemaho 1 3 , Jordan Katine 3 , Eric E Fullerton 3 , Bruce Terris 3
1 , Institut d'Electronique Fondamentale, Orsay France, 3 , HitachiGST, San Jose, California, United States, 2 , LPM , Nancy France
Show AbstractThe observation of magnetization reversal of nano-elements driven by polarized spin currents provides new opportunities to study and control domain structures. The phenomena have been primarily studied in magnetic elements with in-plane magnetic anisotropy. In this talk, we describe our experimental demonstration of domain wall (DW) manipulation driven by spin-currents in wires and nanopillars with perpendicular anisotropy [1-3]. First, we describe the influence of the pinning potential on current driven domain wall depinning process in wires based on spin valves structures. By artificially controlling the strength of the pinning field Hp, we find the threshold current decreases when reducing Hp. In addition, the efficiency of the depinning process is observed to correlate with the amplitude of the giant magnetoresistance effect. This suggests that both extrinsic and intrinsic effects play a role in current-induced DW depinning process. Then, we describe current induced DW creation in nanopillars as small as 50x100nm2. This is achieved using high coercivity Co/Ni multilayer films with perpendicular magnetic anisotropy that support Bloch walls on the order of 10 nm in width. We find that domains can be nucleated with modest current densities of 107 A/cm2. This DW state is stable over a large region of the current-field phase diagram and can be further controlled by CPP currents to restore the uniform states. In addition to the current driven control of DW nucleation and propagation this study clearly demonstrates that the macro-spin model does not provide a full description of magnetic reversal in films with perpendicular anisotropy even for very small nanoelements. The ability to nucleate and manipulate domain walls by a current provides new prospects for ultra high density spintronic devices.[1] D. Ravelosona, D. Lacour, J.A. Katine, B.D. Terris, and C. Chappert, Phys. Rev. Lett. 95, 117203 (2005)[2] S. Mangin, D. Ravelosona, J. Katine, B. Terris, E.E. Fullerton, Nature Materials 5, 210 (2006)[3] D. Ravelosona, S. Mangin, Y. Lemaho, J. Katine, B. Terris, E.E. Fullerton, Phys. Rev. Lett 96, 186604 (2006)
3:30 PM - P3.3
Non-volatile Spin Memory Based on Electrically Controlled Phase Transition in Magnetic Semiconductor Nanostructures.
Yuriy Semenov 1 , Hani Enaya 1 , John Zavada 2 , Ki Wook Kim 1
1 Electrical Computer Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 US Army Research Office, Research Triangle Park, Raleigh, North Carolina, United States
Show Abstract3:45 PM - P3.4
Ab initio Design of Fabrication Process and Shape Control of Self-organized Tera-bit-density Nano-magnets in Dilute Magnetic Semiconductors by Two-dimensional Spinodal Decomposition.
Tetsuya Fukushima 1 , Kazunori Sato 1 , Hiroshi Katayama-Yoshida 1 , Peter Dederichs 2
1 , The Institute of Scientific and Industrial Research, Osaka University, Osaka Japan, 2 , Institut fuer Festkoerperforschung, Forschungszentrum Juelich, Juelich Germany
Show AbstractDue to the discovery of carrier induced ferromagnetism in dilute magnetic semiconductor (DMS), people try to realize semiconductor spintronics devices (such as spin-based THz-switching device, Tera-bit-density nano-magnets, energy-saving and nonvolatile spintronics devices) by using the ferromagnetic DMS. However, the ferromagnetism in DMS is very complicated phenomena and now it is recognized that the practical use of DMS for semiconductor spintronics application is non-trivial problem. For example, we showed that magnetic impurities form quasi-one-dimensional nano-structures in DMS due to two-dimensional spinodal decomposition under the layer-by-layer crystal growth condition, and pointed out that the blocking phenomena in the super-paramagnetism, the magnetic dipole–dipole interaction and the formation of the network in the quasi-one-dimensional nano-structures should be considered to understand the magnetism in DMS. However, we also pointed out that the quasi-one-dimensional nano-structure can be utilized as a part of a spintronics device.In this work, we show that design of new fabrication process and shape control method of Tera-bit-density nano-magnets in DMS based on first principles calculations. The requirement for the realization of the semiconductor spintronics is to develop (i) the fabrication method of Tera-bit-density nano-magnets using the self-organization by bottom-up nanotechnology, (ii) the control method of growth position in the atomic level for the system integration on the substrate, and (iii) the shape-control method of the Tera-bit-density nano-magnets for the application of spintronics devices in the DMS. Based on calculated exchange coupling constants and chemical pair interactions by using KKR-CPA (Korringa-Kohn-Rostoker coherent potential approximation) method and magnetic force theorem, we simulate shape control metod of the quasi-one-dimensional nano-magnets. We design a new fabrication process to realize the self-organized Tera-bit-density nano-magnets in the DMS by controlling the two-dimensional spinodal decomposition under the layer-by-layer crystal-growth condition. We show that the position and density of nano-magnets can be controlled by nano-scale seeding using the lithography at the atomic scale on the substrate, and also demonstrate that the shape of quasi-one-dimensional nano-magnets along the crystal growth direction is controlled by changing the vapor pressure or concentration of the magnetic impurities during the thermal non-equilibrium crystal growth, such as MBE, MOVPE or MOCVD method.
P4: FePt Nanoparticles
Session Chairs
Wednesday PM, November 29, 2006
Room 309 (Hynes)
4:30 PM - **P4.1
Magnetism and Structure of FexPt1-x Nanocubes, -spheres , Icosaeders and Cuboctaeders.
Michael Farle 1
1 Physik, Universitaet Duisburg-Essen, Duisburg Germany
Show AbstractMonodisperse magnetic FexPt1-x nanoparticles with different shapes and compositions have been prepared by organometallic synthesis and gasphase condensation in well controlled sizes ranging from 3 – 10 nm. The structure and magnetism on the atomic scale has been studied by combining superpara-/ferromagnetic resonance, different x-ray absorption spectroscopies (EXAFS, XMCD, XAFS) and Z-contrast and element-specific high resolution transmission electron microscopy (HR-TEM and STEM). Examples for a layer resolved outward relaxation of lattice planes in FePt icosaeders and enlarged lattice constants in colloidal FePt particles will be shown. The analysis of the magnetic moments at the Fe and Pt sites shows remarkable differences depending on the chemical state of the nanoparticle, i.e. a) ligand coated, b) after removal of the ligands and surface oxides and c) after annealing of the metallic particles to 800 K. In ligand and oxide free colloidal FexPt1-x nanoparticles (6 nm), which have been annealed to 800 K, we find enhanced (330 %) orbital magnetism at the Fe site and a reduced orbital magnetism at the Pt site. Evidence for a non-homogeneous distribution of Fe and Pt in the particles is demonstrated.Supported by Deutsche Forschungsgemeinschaft SFB 445, and EU network “Syntorbmag”.
5:00 PM - **P4.2
FePt Nanoparticles from a Cluster Source: From L1|*bsub*|0|*esub*| Ordering Kinetics to a Regular Particle Arrangement.
Bernd Rellinghaus 1 , Elias Mohn 1 , Ute Queitsch 1 , Franziska Schäffel 1 , Ludwig Schultz 1 , Anke Blüher 2 , Michael Mertig 2
1 Institute for Metallic Materials, IFW Dresden, Dresden Germany, 2 Max-Bergmann-Center for Biomaterials, University of Technology Dresden, Dresden Germany
Show AbstractAlthough a breakthrough as an application is not yet in sight, L10 ordered tetragonal FePt is still among the most intensively studied materials when it comes to pushing the superparamagnetic limit towards minimum particle sizes for future ultra-high density magnetic data storage media. However, the simultaneous achievement of L10 order, monodispersity, regular particle arrangement, and magnetic texture is yet to be shown. The present talk reviews the potential of FePt nanoparticles from a cluster source in order to reach this goal.Fe-Pt nanoparticles are prepared by DC magnetron sputtering in an inert gas atmosphere and subsequently ejected into high vacuum via differential pumping. The particles may then be subjected to either size fractionation by means of a quadrupole mass filter and / or in-flight thermal annealing in a light furnace prior to their deposition onto a substrate. It is shown that optical annealing of particle agglomerates for times as short as 1 ms leads to inter-particle coalescence. At maximum electrical powers of the light furnace of P = 4.2 kW, the obtained particles are fully sintered to single spherical particles and exhibit the L10 order. These findings can be explained by simply assuming that the volume diffusion of the least diffusing constituent, Pt, is the decisive factor for the L10 ordering kinetics. This is confirmed by the fact that experimental results obtained from bulk, thin film, and nanoparticulate materials, respectively, which cover several decades of annealing times can all be explained by this argument. In order to explore the possibilities of a regular arrangement of the gas phase prepared particles on a substrate, we have used S-layers of Bacillus sphaericus NTCT 9602 as bio-templates. This type of S-layer exhibits p4 symmetry and a regular square lattice of pores with a lattice constant of 12.5 nm. Sheets of this S-layer were deposited onto amorphous carbon films, which were then exposed to a beam of FePt nanoparticles under high vacuum conditions. Structural characterization of the samples was carried out by TEM. Fourier analysis of areas of the samples, where the FePt particles hit the S-layer sheets, revealed a preferred inter-particle distance of about 12.5 nm, which is precisely the lattice constant of the protein crystal. Additional investi¬gations show that a) the structure of the S-layer remains unaltered upon particle deposition and b) the majority of the particles were located in the pores of the bio-template.
5:30 PM - P4.3
Cluster-Assembled Iron-Platinum Nanocomposite Permanent Magnets.
Xiangxin Rui 1 3 , Zhiguang Sun 2 3 , Yingfan Xu 2 3 , David Sellmyer 2 3 , Jeffrey Shield 1 3
1 Mechanical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 3 Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska, United States
Show AbstractExchange-spring nanocomposite permanent magnets have received a great deal of attention for their potential for improved energy products. Predicted results, however, has been elusive. Optimal properties rely on a uniformly fine nanostructure. Particularly, the soft magnetic phase must be below approximately 10 nm to ensure complete exchange coupling. Inert gas condensation (IGC) is an ideal processing route to produce sub-10 nm clusters. Two distinct nanostructures have been produced. In the first, Fe clusters were embedded in an FePt matrix by alternate deposition from two sources. Fe cluster content ranged from 0 to 30 volume percent. Post-deposition multi-step heat treatments converted the FePt from the A1 to L10 structure. An energy product of approximately 21 MGOe was achieved. Properties deteriorated rapidly at cluster concentrations above 14 volume due to uncoupled soft magnetic regions (from cluster-cluster contacts) and cooperative reversal. The second nanostructure, designed to overcome those disadvantages, involved intra-cluster structuring. Here, Fe-rich Fe-Pt clusters separated by C or SiO2 were fabricated. Phase separation into Fe3Pt and FePt and ordering was induced during post-deposition multi-step heat treatments. By confining the soft and hard phases to individual clusters, full exchange coupling was accomplished and cooperative reversal between clusters was effectively eliminated. An energy product of more than 25 MGOe was achieved, and the volume fraction of the soft phase was increased to greater than 0.5 while maintaining a coercivity of 6.5 kOe. The results provide new insight into developing high energy product nanostructured permanent magnets.Research was supported by the U.S. National Science Foundation through the Materials Research Science and Engineering Center QSPINS at the University of Nebraska.
5:45 PM - P4.4
Inter-particle Magnetic Interactions in Nanoparticle Compacts.
Chuanbing Rong 1 , Vikas Nandwana 1 , Naranyan Poudyal 1 , Yang Li 1 , J.Ping Liu 1 , Mikhail E Kozlov 2 , Anvar Zakhidov 2 , Ray Baughman 2
1 Department of Physics, University of Texas at Arlington, Arlington, Texas, United States, 2 NanoTech Institute, University of Texas at Dallas, Richardson, Texas, United States
Show Abstract
Symposium Organizers
Juergen Fassbender Institute of Ion Beam Physics and Materials Research
John Chapman University of Glasgow
Caroline A. Ross Massachusetts Institute of Technology
P5: Magnetic Anisotropy
Session Chairs
Thursday AM, November 30, 2006
Room 309 (Hynes)
9:30 AM - **P5.1
Anisotropy of Bimetallic 2D Nanostructures.
Harald Brune 1
1 Physics, EPFL, Lausanne, VD, Switzerland
Show Abstract10:15 AM - P5.3
Exchange Coupling, Surface and Configurational Anisotropy in Magnetic Nanoparticles.
Hariharan Srikanth 1
1 Department of Physics, University of South Florida, Tampa, Florida, United States
Show AbstractMagnetic nanostructures are considered basic building blocks in spin-electronic devices and high-density data storage applications. Surface and configurational effects in nanoparticles have been increasingly found to play significant roles in controlling the magnetic anisotropy. Faceted surfaces, core-shell structures with interface exchange coupling and geometries that favor spin frustration in nanoparticle clusters can contribute to significant enhancement of anisotropy. For example, this could be useful to overcome the superparamagnetic limit. Surface contributions to magnetic anisotropy are difficult to probe using conventional static magnetization experiments. Over the years, we have pioneered the sensitive method of radio-frequency (RF) transverse susceptibility that is unique in terms of its ability to precisely probe such phenomena. We will present and discuss a few case studies involving iron oxide and soft ferrite nanoparticles where dynamic AC and RF susceptibility experiments are used to explore a variety of rich cooperative magnetic phenomena arising from exchange coupling, surface anisotropy, ‘memory’ effect and relaxation processes. Overall, we demonstrate that RF susceptibility experiments are ideally suited to characterize magnetic properties as well as explore new physics in nanostructured magnetic materials.
Work supported by NSF (0408933) and the Army (W911NF-05-1-0354)
10:30 AM - P5.4
Magnetic Anisotropy Probed by High Momentum Resolution Electron Energy-Loss Spectroscopy.
Yasuo Ito 1 2 , Nestor Zaluzec 2 , Russell Cook 2 , Dean Miller 2
1 Physics, Northern Illinois University, DeKalb, Illinois, United States, 2 Materials Science Division, Argonne National Laboratory, Chicago, Illinois, United States
Show AbstractTremendous efforts have been focused on fabrication and characterization of nanomagnetic structures for the spin-based electronics. Since the spin transport occurs through the bulk of multi-layered nanostructures, probes directly sensitive to the magnetic anisotropy of the bulk and its interfaces are of great interest. Particularly, there is an urgent need for a technique capable of probing the magnetic anisotropy on length scale less than a few nanometers. Magnetic Linear Dichroism (MLD) is an often used method to study magnetism which is facilitated by studying changes in X-ray Absorption Near Edge Structure measured at Synchrotron radiation sources. In an electron scattering experiment, Electron Loss Near Edges Structure can be also employed to study MLD. In this case, we make use of the fact that the perturbing electric field (of an incident electron probe) is longitudinally polarized in the direction parallel to the momentum transfer and thus can be used to probe the electronic and magnetic structure of a material [1]. So far, the possibility of detecting nanometer scale MLD on an oriented hematite crystal, using Momentum (angular)-Resolved Electron Energy-Loss Spectroscopy have been presented using a focused electron probe of STEM [1,2,3]. However, due to the use of a focused probe, angular (momentum) resolution of those spectra was not optimized, leaving some inconsistent results in some cases. In this study, magnetic anisotropy (MLD) is observed by using the high angular resolution electron channeling electron spectroscopy (HARECES) facilities in the ANL EM Center. In HARECES we employed computationally mediated control of the electron microscope which permits spectroscopic measurements at angular resolutions as small as 0.05 mR, allowing momentum resolved spectra to be recorded which is sensitive to the anisotropic orientation dependence of the magnetic spin in layered materials. In our initial work we have verified the ability of our methods to measure MLD, by studying the changes in core loss spectra taken from 3-d transition metals in different magnetic states. We have observed changes of spectra not only due to the change of band structure but also due to the effect of the Lorentz force by the magnetic domain. We will further apply this technique to 3-d transition metal oxides as well as rare earth materials, which can be a part of spin-electronic device structures, and will focus on establishing optimum conditions for measurements with the highest spatial resolution allowing us to probe the changes at magnetic domain interfaces.[1] J. Yuan, N.K. Menon, J. Appl. Phys. 81, (1997) 5087; N.K. Menon, J. Yuan, Ultramicroscopy 78, (1999) 185. [2] Y. Ito et al., Microscopy and Microanalysis 9 Suppl. 2, (2003) 314CD. [3] P.A. van Aken, S. Lauterbach, Phys. Chem. Minerals 30 (2003) 469. [4] This work is supported by the U.S. Department of Energy, Basic Energy Sciences-Materials Sciences, under Contract #W-31-109-ENG-38.
10:45 AM - P5.5
Magnetic Interactions and Size Effects in 3d(Fe,Co)–5d/4d(Pt,Pd) Nano-structures.
Oleg Mryasov 1
1 , Seagate Research, Pittsburgh, Pennsylvania, United States
Show AbstractP6: Domain Walls and Dynamics
Session Chairs
Thursday PM, November 30, 2006
Room 309 (Hynes)
11:30 AM - **P6.1
Domain-Wall Dynamics in Permalloy Microstructures.
James Erskine 1 , G. Beach 1 , C. Nistor 1 , C. Knutson 1 , S. Yang 1 , F. Liu 1 , M. Tsoi 1
1 Physics, University of Texas at Austin, Austin, Texas, United States
Show AbstractThursday 11/30New Presenting Author*P6.1 10:30 amDomain-Wall Dynamics in Permalloy Microstructures. C. Nistor.
12:00 PM - P6.2
Transport Study of Domain Walls Induced by an Exchange Tab in Magnetic Nanowires.
Sunny Lua 1 2 3 , Yi Hong Wu 2 , Kie Leong Teo 2 , Tow Chong Chong 3
1 NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore Singapore, 2 Department of Electrical and Computer Engineering, National University of Singapore, Singapore Singapore, 3 , Data Storage Institute, Singapore Singapore
Show AbstractMagnetic domain walls (DWs) have attracted renewed interest recently due to the potential applications in read sensor, memory [1] and logic devices [2]. The advance in nanofabrication has made it possible to study domain walls in magnetic nanostructures, in particular one-dimensional nanostructures in a more controllable fashion. So far, most of the work has been focused on the creation of domain walls using geometrical constrictions [3]. This type of structure, however, makes it difficult to study the intrinsic resistance of domain walls due to the not well-defined local current directions in the constricted region as well as the boundary scattering effect. To minimize the geometrical effect in domain wall resistance study, we used an exchange tab to create DWs in sub-micron magnetic wires and studied their transport properties. The exchange tab consists of a small segment of ferromagnet layer coupled antiferromagnetically to a small portion of the magnetic wire via a thin Ru spacer. The exchange tab, having a synthetic antiferromagnetic multilayer of NiFe (10nm) / Ru (0.8nm) / NiFe (6nm) / Ta (3nm), is fabricated using e-beam lithography in combination with ion milling. The top NiFe was patterned together with Ru to form the tab, while the bottom NiFe layer is continuous for probing the magnetoresistance (MR). The formation of domain walls has been confirmed by MFM and magnetoresistance measurement. The MR curves are different from those of magnetic wires with small constrictions. 3-D micromagnetic modeling has been carried out on wires with and without exchange tabs. A good agreement has been obtained between experimental and simulation results. [1] S.S.P. Parkin, U.S. Patent No 6834005 (2004).[2] D.A. Allwood et al., Science 309, 1688 (2005).[3] S.H. Florez et al., J. Appl. Phys. 95, 6720 (2004).
12:15 PM - P6.3
Switching of Magnetic Rings with GHz Irradiation and sub-ns Magnetic Field Pulses.
Jan Podbielski 1 , Dirk Grundler 2
1 Institut fuer Angewandte Physik, Universitaet Hamburg , Hamburg, Hamburg, Germany, 2 Physik-Department E10, Fakultaet fuer Physik, Technische Universitaet Muenchen, Garching, Bayern, Germany
Show AbstractDue to the rapid increase of areal densities in magnetic storage devices, nanostructured ferromagnets have become the focus of intense research. Here, well-defined remanent states and reproducible ultrafast switching are important aspects [1]. We have investigated nanostructured rings which were prepared from 20 nm thick permalloy [Ni(80)Fe(20)] and integrated to a broadband coplanar waveguide (CPW). The rings had an outer diameter of 2 µm and a width down to 150 nm. At remanence they exhibited either a polarized onion state or a stray-field free vortex state which, both, could in principle be used for storing magnetic information. To explore the dynamics and switching of these states we performed GHz spectroscopy [2-4] and, recently, time-resolved experiments where we have used sub-ns magnetic field pulses. In case of GHz irradiation which is applied quasi continuously we observe microwave-assisted switching. This process is very effective, i.e., the amplitude is smaller than the static switching field, and seems to occur resonantly at a characteristic spin wave eigenfrequency of the ring. For sub-ns pulses in the CPW much larger magnetic field amplitudes are needed to induce the switching. We will compare our data with recent experiments on precessional switching of micromagnets [5] and on reversal of nanocrystals by nonlinear resonance [6]. We thank for financial support by the DFG via SFB668.[1] See, e.g., IBM Journal of research and development 50 (1), 2006 at http://www.research.ibm.com/journal/rd50-1.html.[2] F. Giesen et al., Appl. Phys. Lett. 86, 112510 (2005).[3] F. Giesen et al., J. Appl. Phys. 97, 10A712 (2005).[4] J. Podbielski et al., Phys. Rev. Lett. 96, 167207 (2006). [5] Th. Gerrits et al., Nature 418, 509 (2002).[6] C. Thirion et al., Nat. Mater. 2, 524 (2003).
12:30 PM - P6.4
Oersted Field in Perpendicularly Magnetized Point Contact Nano-oscillators Induce a Magnetic Vortex.
Mark Hoefer 1 , Thomas Silva 1
1 , NIST, Boulder, Colorado, United States
Show AbstractThe Oersted field contribution to the magnetic torqueequation modeling point contact, spin transfer nano-oscillators with a perpendicularly applied field is considered. The symmetry of this case forces the magnetization to be pinned in the center of the pointcontact. This two dimensional problem is shown to be equivalent to an effectively one dimensional model where large-amplitude, weakly localized magnetic vortices radiating radial spin waves are computed. These vortex states have odd symmetry hence are geometrically verydifferent from the well known Slonczewski cylindrical modes with even symmetry found in the case of zero Oersted field. However, numerical simulations of the fully nonlinear model show many similarities between the two cases. For example, the oscillator frequency as a function of current is just slightly upshifted in the Oersted field case due to the higher exchange energy associated with the vortex state.The stability of the polarity of the vortex state will also be discussed.
12:45 PM - P6.5
Ferromagnetic Resonance Studies of Co/Ni Multilayer Films and Nanometer Scale Elements.
Jean-Marc Beaujour 1 , Wenyu Chen 1 , Andrew Kent 1 , Jonathan Sun 2
1 Physics Department, New York University, New York, New York, United States, 2 , IBM T. J. Watson Research Center, Yorktown Heights, New York, United States
Show AbstractMagnetization dynamics in confined systems is a topic of great current interest. It has recently become possible to study magnetic excitations in individual nanomagnets using ferromagnetic resonance (FMR), generated by a spin-torque (ST) interaction [1]. Here we report on a comparison of conventional broadband FMR on extended thin films with ST FMR excitation of the same films patterned down to 50 nm scale lateral dimensions using electron beam lithography. Experiments are conducted on || [xCo – 2[x Ni] × Ν | 10nm Cu | 12 nm Co|| structures, where x is the thickness of the Co layer. Varying x is shown to enable variation of the easy-plane anisotropy. Samples with x = 0.1, 0.2, 0.3 and 0.4 nm have been studied, where the number of bilayers is varied to keep the film thickness and total magnetic moment constant (N =1.2/x, x in nm). The samples were grown on Si-SiO2 substrate by evaporation in UHV. Field sweep FMR measurements on extended films and nanopillar devices were conducted in a broad frequency range in the GHz regime (1 to 20 GHz). FMR studies of the thin films were carried out using a coplanar waveguide and the flip-chip method. The resonance field Hres and the linewidth ΔH were studied as a function of frequency for field-in plane and field perpendicular to the plane, and as a function of the field angle at constant frequency. The 2nd and 4th order perpendicular anisotropy constants were determined, as well as the magnetic damping parameter, α. ST FMR studies were conducted in the field perpendicular to the plane geometry. The frequency dependence of Hres and ΔH for the nanopillars is compared to that of the extended films.[1] J. C. Sankey et al., Phys. Rev. Lett. 96, 227601 (2006)
P7: Nanoparticles and Applications
Session Chairs
Thursday PM, November 30, 2006
Room 309 (Hynes)
2:30 PM - **P7.1
Magnetic Nanoparticles and Core-shell Structures for Biomedical Applications.
Kannan Krishnan 1 , Marcela Gonzales 1 , Yuping Bao 1 , Saikat Mandal 1
1 Materials Science and Engineering, University of Washington, Seattle, Washington, United States
Show Abstract3:00 PM - **P7.2
Magnetostatic Interactions in Nanoparticle Assemblies.
Sara Majetich 1 , Madhur Sachan 1
1 Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractMonodomain magnetic nanoparticles have found applications in fields ranging from data storage media to biomedicine. They are also of fundamental interest because of theoretical predictions of dipolar ferromagnetism in organized arrays. Three aspects of current interest in magnetic nanoparticles are discussed: control of nanostacle patterning with self-assembly methods, the way that magnetostatic interactions modify isolated monodomain particle behavior, and new methods for probing magnetism on the nanoscale.We focus on monodisperse, surfactant-coated nanoparticles and their ability to form self-organized superstructures. In organic solvents, two-dimensional arrays with long-range order can be formed using Langmuir layer techniques. These monolayers are also used as nanomasks for crystallographically oriented thin films, which provide an alternative approach to preparing nanoparticle arrays for data storage media. Faceted three-dimensional single “grain” nanoparticle crystals are formed by colloidal crystallization methods. The effects of magnetostatic interactions in each of these assemblies is quantified by considering the differences between superparamagnetism, superferromagnetism, and dipolar ferromagnetism. In the nanoparticle arrays of high moment, low anisotropy materials, spin-glass-like behavior is present unless there is a high degree of structural order. This has significance for the magnetic response of composite magnetic particles used in magnetic separations, leading to particle-to-particle variations in the response. For high anisotropy recording media the magnetostatic interactions are well below the switching fields.The nanoscale magnetization patterns of these structures are visualized through three different methods. Small angle neutron scattering provides average magnetic correlation lengths within three-dimensional assemblies, where correlations of hundreds on nanometers may be present at low temperature. Electron holography shows real-space magnetization patterns of magnetic monolayers, where vortices and transverse domain walls are present as low energy excitations. Spin-polarization scanning tunneling microscopy is capable of probing single nanoparticles within a self-assembled monolayer array. Time-dependent measurements of the tunneling current shows differences in the noise spectra as a function of temperature, with a peak that develops around the blocking temperature.
3:30 PM - P7.3
Monodisperse Magnetic Nanoparticles: Chemical Synthesis and Their Potential Nanomagnetic Applications
Shouheng Sun 1
1 Department of Chemistry, Brown University, Providence, Rhode Island, United States
Show AbstractMagnetic nanoparticles are promising building blocks for fabrication of high-performance magnetic nanodevices and important labels for biomedical applications. We demonstrate that monodisperse magnetic nanoparticles of Co, Fe, CoFe, FePt, MFe2O4 (M = Fe, Co, Mn) and NM-MFe2O4 (NM = Au, Ag, Pt, Pd) with controlled size, composition, shape and structure are readily synthesized by solution phase chemical syntheses, and subsequently induced to form 2D and 3D magnetic nanoparticle superlattice arrays via self-assembly. The texture in a self-assembled array is established via self-organization of the shaped nanoparticles. Magnetic properties of these arrays are tuned from superparamagnetic to ferromagnetic with controlled magnetic moment and coercivity. Furthermore, surface modification renders the nanoparticles water soluble and accessible to various biomolecules. These well-engineered magnetic nanostructures are of great importance for deep understanding of nanomagnetism, for fabrication of magnetic nanodevices and for biomedical applications.
3:45 PM - P7.4
Synthesis and Application of Fluorescent Magnetic Nanoparticles Based on Fe3O4@CdSe Core-shell Nanostructures.
Jinhao Gao 1 , Gaolin Liang 1 , Pingbo Huang 2 , Bei Zhang 3 , Xixiang Zhang 3 , Bing Xu 1
1 Department of Chemistry, The Hong Kong University of Science & Technology, Hong Kong, NA, Hong Kong, 2 Department of Biology, The Hong Kong University of Science & Technology, Hong Kong Hong Kong, 3 Department of Physics, The Hong Kong University of Science & Technology, Hong Kong, NA, Hong Kong
Show AbstractFluorescent magnetic nanostructures have attracted broad attention because of their promising applications in biology and biomedicine (e.g., as fluorescent labels for cell imaging, as agents for magnetic resonance imaging). Here we report Fe3O4@CdSe core-shell nanoparticles possessed of both superparamagnetism and fluorescent property. We have reported one-pot synthesis of FePt-CdS heterodimer nanostructures based on FePt nanoparticles as seeds and the themolysis of Cd(acac)2 (J. Am. Chem. Soc. 2004, 126, 5664-5665). FePt-CdS heterodimer nanoparticles, however, have very low quantum yield and can not been easily manipulated by a small magnet because of the relative small magnetic moment of FePt nanoparticles. Therefore, we chose 4 nm Fe3O4 nanoparticles with larger magnetic moment as seeds to make Fe3O4@CdSe core-shell nanostructures. After dispersing Fe3O4 in a organic solvent, we added CdO powder into the mixture at high temperature to create Cd shell, which was converted to CdSe shell by the subsequent addition of selenium because CdSe nanocrystals made by using CdO as precursor have very high quantum yield. The as-prepared Fe3O4@CdSe core-shell nanoparticles were characterized by means of transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDX), selected area electron diffraction (SAED), and X-ray photoelectron spectroscopy (XPS). The magnetic property of Fe3O4@CdSe core-shell nanoparticles was measured by SQUID. Fe3O4@CdSe core-shell nanoparticles give fluorescent emission maxima 610 nm (shows red color in UV light) and can be attracted by a small magnet quickly. Fe3O4@CdSe nanoparticles can be uptaken easily by cells, as confirmed by confocal experiment. These novel nanomaterials should find potential biological applications such as sensors, controllable cell imaging to the targeted substrates in vitro and in vivo.
P8: Assembly of Nanoparticles
Session Chairs
Thursday PM, November 30, 2006
Room 309 (Hynes)
4:30 PM - P8.1
Synthesis and Magnetic Properties of Co Nano-rod Superlattices.
Fabienne Wetz 1 , Katerina Soulantika 2 , Marc Respaud 2 , Bruno Chaudret 1
1 Laboratoire de Chimie de Coordination, CNRS, Toulouse France, 2 Laboratoire de Nanophysique Magnétisme et Optoélectronique, INSA, Toulouse France
Show AbstractShape control and self-assembly of magnetic nanoparticles have great importance in nanotechnology. The problem of magnetic materials, as media for the high density magnetic storage is a representative example where chemically synthesized “hard” magnetic nanoparticles can play a determinant role. For densities above the Terabits/inch2, the lateral size of each bit should be smaller than 10nm. The ideal media require well defined nanoparticles, regularly organised into arrays, in order to address them with precision. An increase of the density implies the reduction of the size of the nano-objects. A system based on a monolayer of self-organised nanorods oriented perpendicular to the plane would be an elegant solution for achieving a large density and a sufficiently large magnetic volume to displace the superparamagnetic limit above room temperature.We present the synthesis and magnetic properties of Co nanorods spontaneously organised in superlattices over a surface of several microns. The decomposition reaction under hydrogen of Co[N(SiMe3)2]2 in the presence of a long chain amine and a long chain acid as shape control agents, leads to cobalt nanorods. This synthetic procedure permits a remarkable control over the size distribution of the nanorods. The nanorods are monocrystals, displaying a hexagonal compact bulk phase with the c-axis being the long axis of the nanorods. They are organized side by side along their long axis, in a direction perpendicular to the substrate exposing a surface of tips. Such layers are superposed forming unprecedented 3D superstructures. We are able to modify the length of the produced nanorods without any significant modification of their diameter by varying the reaction time and the hydrogen pressure and keeping all other parameters constant (ligand nature, ligand ratio, temperature, solvent). Concerning their organisation in superlattices, even if we cannot rule out the influence of magnetic dipolar interactions due to the magnetic moment of the nanorods, the organic ligands which surround the nanorods should play a major role.These nanorod superlattices are ferromagnetic at r.t. and they are characterized by a strong coercive field (1,2T at 2K), as a consequence of their large magnetic anisotropy (magnetocrystalline and shape). The magnetisation measured after the field cooling procedure from 300K down to 2K under a magnetic field of 5T lead to a higher remnant magnetisation and a stronger coercive field. Interestingly, the hysteresis loop remains symmetric, which is a clear indication that no thick Co-oxide layer has been formed on their surface. We interpret the increase of the remnant magnetisation as a result of a possible reorientation of the entire group of the organised nanorods by the magnetic field, as a consequence of the large magnetic anisotropy of the nanorods. The direct synthesis of nanorods on magnetic flat substrates is the next step towards their application in high density magnetic storage.
4:45 PM - P8.2
Very Large FeCo Nanoparticles Super-lattices: Magnetic and Transport Properties.
Celine Desvaux 1 2 , Reasmey Tan 3 , Julian Carrey 3 , Marc Respaud 3 , Philippe Renaud 2 , Bruno Chaudret 1
1 , LCC CNRS, Toulouse France, 2 , Freescale Semiconductor, Toulouse France, 3 , LNMO-INSA, Toulouse France
Show AbstractThe integration of nano-objects into micro- or nano-devices requires the elaboration of strictly monodisperse nanoparticles and their their organization on a very long scale under the form of super-lattices. In addition, these super-lattices have to be elaborated on a substrate on which they will in certain cases be electrically addressed. It is therefore necessary to develop new synthetic techniques able to produce very large organizations of monodisperse particles which can be easily integrated in the present processes of microelectronics (magnetic nanoparticles for inductors), or to lead to novel nano-devices (organized nanoparticles for magnetoresistive devices).Our group has developed strategies to synthesize monodisperse nanoparticles of various sizes and shapes included or not into super-lattices.[1, 2] Here we report the one step synthesis of millimetre long 3D super-lattices of Fe0.6Co0.4 nanoparticles using an organometallic chemical method.[3] The 15 nm diameter spherical particles display an unusual polytetrahedral phase that becomes bcc after a thermal treatment. The material is obtained either as crystals of particles in which they display an fcc organization, or crystallized on a silicon substrate on which the particles self-organize into packed arrays. Furthermore, the crystals can be re-dissolved as single particles in a solvent to be further re-deposited on a substrate. Finally, the material can undergo various treatments to protect the particles from oxidation. The magnetic and transport properties are very rich: we observed a novel mechanism of magnetoresistance, an unprecedented magnitude (3000 %) of high-field magnetoresistance in such a structure, and conduction phenomena which are attributed to the formation of a Coulomb glass. RF measurements show a ferromagnetic resonance at 2.5 GHz.[1]F. Dumestre, B. Chaudret, C. Amiens, P. Renaud, P. Fejes, Science 2004, 303, 821.[2]K. Soulantica, A. Maisonnat, M. C. Fromen, M. J. Casanove, B. Chaudret, Angew. Chem. Int. Ed. Engl. 2003, 42, 1945.[3]C. Desvaux, C. Amiens, P. Fejes, P. Renaud, M. Respaud, P. Lecante, E. Snoeck, B. Chaudret, Nature Materials 2005, 4, 750
5:00 PM - P8.3
Evolution of Fe-Co Magnetic Alloys: from Thin Films to Catalyst Nanoparticles for Carbon Nanofiber Synthesis
Kate Klein 1 2 4 , Anatoli Melechko 1 3 4 , Jason Fowlkes 1 2 , Korey Sorge 5 , Theodora Leventouri 5 , Ryan Rucker 2 , Philip Rack 3 4 , Michael Simpson 1 2 3
1 Molecular Scale Engineering & Nanoscale Technologies Research Group, Oak Ridge National Laboratory, Oak Ridge , Tennessee, United States, 2 Materials Science and Engineering, University of Tennessee, Knoxville , Tennessee, United States, 4 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge , Tennessee, United States, 3 Material Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge , Tennessee, United States, 5 Department of Physics, Florida Atlantic University, Boca Raton, Florida, United States
Show AbstractRemarkably, as most of the catalyst metals used in carbon nanostructure synthesis are well known ferromagnets in a bulk phase, the co-synthesis of these carbon nanostructures and magnetic nanoparticles presents a unique opportunity to study the fundamental aspects of magnetic alloy behavior under nanoscale confinement. In this work we investigate alloy catalyst systems, in particular iron-cobalt, for the synthesis of vertically aligned carbon nanofibers (VACNFs) and the formation of magnetic nanoparticles in a dc plasma enhanced chemical vapor deposition (PECVD) process. The nanoparticle formation is studied at several stages in development. Thin alloy films are deposited onto bare silicon or a titanium buffer layer on silicon. The films are then broken down into individual nanoparticles during a brief pre-etch in an ammonia plasma at elevated temperatures. With the addition of acetylene gas, nanoparticle is lifted off the substrate by the catalytically growing carbon nanofiber and is molded by a complex interaction with the graphitic structure. Finally, cooling and post-synthesis annealing sets the alloy arrangement within carbon capsule. This evolution of alloy thin films to carbon encapsulated nanoparticles is traced using scanning electron microscopy, high resolution transmission electron microscopy, electron spectroscopy, x-ray diffraction and magnetometry characterization techniques.
5:15 PM - P8.4
Nanoscale Magnetic Properties of Self-assembled Ni and Fe Particles in Single and Multilayered Structures.
Alok Gupta 1 , Dhananjay Kumar 1
1 Mechanical & Chemical Engg., North Carolina A & T State University, Greensboro, North Carolina, United States
Show Abstract5:30 PM - P8.5
Simulation of Multilayer Heteroepitaxial Growth of Magnetic Material Using the Phase-Field Model.
Emma Humphrey 1 , Steven Wise 2 , John Lowengrub 2 , Katsuyo Thornton 1
1 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Department of Mathematics, University of California, Irvine, California, United States
Show AbstractSelf-assembled growth of nanoscale vertical magnetic pillars is simulated using a phase-field model. Using the Cahn-Hilliard evolution equation with source terms, we study alternating heteroepitaxial deposition of a strained magnetic material and nonmagnetic material on a nonmagnetic substrate. The first deposition layer of the magnetic material forms a strained thin film. The film self-assembles into dots to reduce strain energy. Due to surface thermodynamics and elastic mifit, consecutively deposited magnetic dots self-assemble above the sublayer dots, forming vertical magnetic stacks with high lateral packing. Because the dots forming the stacks are magnetically coupled, each stack behaves as a single magnetic unit whose superparamagnetic blocking temperature decreases with increasing stack size. The phase-field simulations are employed to study the formation and the stability of the magnetic columns and to examine substrate patterning as a means for directed self-assembly.
5:45 PM - P8.6
Controlled Growth and Magnetic Properties of Self-Assembled Co and Fe Nanoparticles on Single Crystalline Insulating Layers
Minn-Tsong Lin 1 2 , Wen-Chin Lin 1 2 , Po-Chun Huang 1 , Shen-Shing Wong 1 , Chii-Bin Wu 1 , Bin-Rui Xu 1 , Cheng-Tien Chiang 1 , Hong-Yu Yen 1 , Chien-Cheng Kuo 1 , Ker-Jar Song Song 2
1 Department of Physics, National Taiwan University , Taipei Taiwan, 2 Institute of Atomic and Molecular Sciences , Academia Sinica, Taipei Taiwan
Show AbstractWe report controlled growth and magnetic properties of Co and Fe self-aligned nanoparticle chains vapor-deposited over a single crystalline Al
2O
3 layers on NiAl(100) with advantages including: self-limiting size distribution with the average size of ~ 2.7 nm, one-dimensional well-ordered alignment, and high thermal stability. We attribute the excellences to peculiar one-dimensional long stripes with ~ 4 nm interdistance on the surface of the ultrathin Al
2O
3 template. The results of tunneling microscopy and spectroscopy study connect this self-alignment to a superior trapping ability due to enhanced density of state located at the one-dimensional stripes on single-crystalline Al
2O
3 layers. Based on the systematic studies of the growth temperature, deposition rate and annealing effects, the control of Co nanoparticle density, size and alignment are demonstrated to be feasible on this nano-structured template, indicating the possibilities of the controlled growth for nanoparticles of various materials.The ferromagnetism of Fe nanoparticle assembly on Al
2O
3/NiAl(100) is observed above 150 K only with the coverage larger than 5 monolayer (ML). Cu capping layer induces an enhancement of the Curie temperature (T
C) in both Fe and Co magnetic nanoparticle assembly. The T
C of Fe nanoparticle assembly with 2 ML and 6 ML Cu capping layer is enhanced by ~ 20 K and even higher, indicating the critical effects of metallic capping layer in such magnetic nanostructures as nanoparticle assembly. The magnetic domain imaging of nanoparticle assembly with and without capping layer is also presented with help of the technique of Scanning Electron Microscopy with Polarization Analysis (SEMPA). The capping layer effect would be crucial for the ex-situ measurements and the nanostorage-related applications.*E-mail:
[email protected] References: [1] S. Gwo, C.-P. Chou, C.-L. Wu, Y.J Ye, W. C. Lin, and Minn-Tsong Lin, Phys. Rev. Lett. 90, 185506 (2003)[2] W.C. Lin, C. C. Kuo, M.F. Ro, K. J. Song, and Minn-Tsong Lin, Appl. Phys. Lett. 86, 043105 (2005) [3] W. C. Lin, P. C. Huang, K. J. Song, and Minn-Tsong Lin, Appl. Phys. Lett. 88, 153117 (2006)
P9: Poster Session: Magnetic Films, Patterned Structures and Molecular Magnets
Session Chairs
John Chapman
Jurgen Fassbender
Caroline Ross
Friday AM, December 01, 2006
Exhibition Hall D (Hynes)
9:00 PM - P9.1
Investigation of Element Specific Hysteresis Loops of ion-induced Magnetically Patterned Ni81Fe19/Ru/Co90Fe10 Films with Magnetic Soft X-ray Microscopy.
Karsten Kuepper 1 , Lothar Bischoff 1 , Roland Mattheis 2 , Peter Fischer 3 , Dong-Hyun Kim 3 , Jurgen Fassbender 1
1 Institute of Ion Beam Physics and Materials Research, Forschungszentrum Rossendorf, Dresden Germany, 2 , Institute for Physical High Technology, Jena Germany, 3 Lawrence Berkeley National Laboratory, Center for X-ray optics, Berkeley, California, United States
Show AbstractWe present a layer resolved magnetic soft x-ray microscopy study of a RKKY coupled Ni81Fe19/Ru/Co90Fe10 layered system where magnetic patterns were imprinted by using a 60 keV fine focused Co ion beam so as to change the coupling from antiferromagnetic to ferromagnetic on a micron scale. Thereby artificial structures in form of stripes with locally varying interlayer exchange coupling are generated. Utilizing the elemental specificity of high-resolution full field soft x-ray microscopy at the Co L3 and the Ni L3 edges we determined the magnetic domain configuration during full magnetization reversal processes locally and layer resolved. In addition to the locally varying interlayer exchange coupling across the Ru layer our data verify a direct exchange coupling within each ferromagnetic layer in the magnetically patterned structure. We conclude that the magnetization reversal behaviour of the irradiated stripes is largely influenced by the surrounding magnetic film for both, the Permalloy and the Co90Fe10 layer.
9:00 PM - P9.10
Current Perpendicular to Plane Giant Magnetoresistance in Electrodeposited CoNi/Cu Multilayer Nanowires
Xueti Tang 1 , Gwo-Ching Wang 1 , Mutsuhiro Shima 2
1 Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractWe have investigated the layer thickness dependence of giant magnetoresistance (GMR) in the current-perpendicular-to-plane (CPP) geometry for electrodeposited CoNi/Cu multilayer nanowires. We have found evidence that supports the Valet-Fert (V-F) model [1] for CPP spin dependent transport, which takes into account the spin accumulation and spin relaxation effects. The GMR effect in the CPP geometry often gives a larger GMR value than that in the current-in-plane (CIP) geometry. It is also advantageous to study the CPP-GMR in order to test theoretical models and to evaluate various significant parameters of the spin transport [2]. The measurement of CPP-GMR using conventional multilayer thin film systems is inherently challenging because of the very small resistance due to the relatively small layer thickness and large lateral dimension. Multilayer nanowires consisting of alternating magnetic and nonmagnetic layers are ideal for investigating the CPP-GMR since the high aspect ratio of the nanowire gives larger resistance values so that more accurate measurements of GMR can be facilitated. In this work, CoNi/Cu multilayer nanowire samples were prepared by potentiostatic electrodeposition using 60 μm-thick alumina templates which have an average pore size of ~250 nm. The CPP-GMR measurements of the nanowires were carried out using a metallic plunger tip to make a point contact to the mechanically polished side of the template. A conducting tape on the seed layer side of the template connecting to an external conducting wire completes the current loop. This method enables us to measure the CPP-GMR at various locations of each sample and to measure different numbers of nanowires. We found that the GMR ratio is nearly independent of the number of nanowires measured. The GMR ratio exceeding 25% has been observed at room temperature in multilayer nanowires of nominal layer thicknesses t(Cu) = 3 nm and t(CoNi) = 7 nm. When both t(Cu) and t(CoNi) are much smaller than the spin diffusion length l of the corresponding materials, i.e. t(Cu) << l(Cu) and t(CoNi) << l(CoNi), the one over square root of the GMR ratio varies linearly with increasing t(Cu). This result agrees well with the V-F model. However, when t(Cu) << l(Cu) and t(CoNi) >> l(CoNi), the reciprocal of GMR ratio does not linearly change with t(CoNi), indicating a departure from the prediction of the V-F model. This deviation is attributed to the effect of anisotropic magnetoresistance (AMR). [1] T. Valet and A. Fert, Phys. Rev. B 48, 7099 (1993).[2] J. Bass and W.P. Pratt Jr., Physica B 321, 1 (2002).This research is supported by National Science Foundation Award No. 05 06 738.
9:00 PM - P9.11
Electrochemical Template Synthesis of Magnetic Nanorings and Nanotubes.
Zhu Liu 1 , Peter Searson 1
1 Materials Science & Engineering, Johns Hopkins Univ., Baltimore, Maryland, United States
Show Abstract9:00 PM - P9.12
Synthesis and Physical Properties of Ferromagnetic Semiconducting EuO Nanorods.
Matthew Bierman 1 , Song Jin 1
1 Chemistry, University of Wisconsin-Madison, Madison, WI, Wisconsin, United States
Show AbstractWe report the synthesis, structural characterization, and physical properties of nanorods of the concentrated ferromagnetic semiconductor EuO. This 1.1eV bandgap semiconductor becomes a Heisenberg ferromagnet with a bulk Tc of 69K. One-dimensional building blocks of this interesting material are being fabricated for use in spintronic devices and to investigate the physical properties of this unique material. Crystalline nanorods of Eu(OH)3 are precipitated in a facile reaction from aqueous solution, converted in a solid state reaction in air to Eu2O3, and reduced in a Eu vapor to EuO. Identity has been confirmed with powder x-ray diffraction. Nanorod morphology has been monitored with scanning electron microscopy and transmission electron microscopy. SQUID magnetometry has confirmed the ferromagnetic nature of the nanorods, and shown a Curie temperature of around 75K. The rods show a saturation magnetization of 165 emu/g at an applied field of 1 Tesla. Hysteresis is clearly seen below the Curie temperature. The magneto-optical properties have also been measured by Magnetic Circular Dichroism (MCD). MCD is seen in transitions associated with 4f7->5dt2g and 4f7->5deg absorption. A shift further towards the IR is seen for the 4f7->5dt2g transition as temperature is decreased. The MCD spectra give evidence of enhanced Zeeman splitting, which shows a large MCD signal that is consistent with a ferromagnetic semiconductor.
9:00 PM - P9.13
Nanomagnet Arrays Fabricated by Shadow Deposition on Self-organized Semiconductor Templates.
Christian Hofer 1 , Christian Teichert 1 , Miguel Niño 2 , Nikolai Mikuszeit 2 , Julio Camarero 2 , Juan de Miguel 2 , Rodolfo Miranda 2 , Lidia Gridneva 3 , Dimitri Arvanitis 3 , Andrea Locatelli 4 , Stefan Heun 5
1 Institute of Physics, University of Leoben, Leoben Austria, 2 Department of Condensed Matter Physics, Univ. Autónoma de Madrid, Madrid Spain, 3 Department of Physics, University of Uppsala, Uppsala Sweden, 4 , Sincrotrone ELETTRA, Trieste Italy, 5 , TASC-INFM Laboratory, Trieste Italy
Show AbstractSelf-organized nanofaceted semiconductor surfaces are attractive candidates to be used as large-area templates for the growth of magnetic nanostructures [1]. By shadow deposition onto selected facet types, arrays of isolated nanomagnets can be fabricated. Using this technique we prepared Co nanomagnets on {113} faceted SiGe templates at the Nanospectroscopy Beamline of the synchrotron ELETTRA in Trieste [2]. In Photoemission Microscopy experiments with Magnetic Circular Dichroism (XMCD-PEEM) at the Nanospectroscopy Beamline of the synchrotron ELETTRA in Trieste we have been able to image arrays of nanomagnets with remanence at room temperature [2], and dimensions as small as ca. 200 × 30 nm2. Due to their small dimensions and short separations, in-plane magnetized nanomagnets are coupled by dipolar interaction forming micrometer-sized domains. The magnetic coupling is preferentially along the easy axis of the nanomagnets in agreement with micromagnetic simulations. Strategies are proposed to overcome the limitation of magnetic coupling, e.g., by depositing (Co/Pt) multilayers. [1]C. Teichert, Appl. Phys. A 76, 653 (2003).[2]A. M. Mulders, et al. Phys. Rev. B 71, 214422 (2005).This research is supported in the framework of the European Project NAMASOS (Nanomagnets by Self-Organisation, Grant No. STRP 505854-1).
9:00 PM - P9.14
Microstructure and Composition of Fe-B Nanobars
Suiqiong Li 1 , Liling Fu 1 , Chongmin Wang 2 , Scott Lea 2 , Mark Engelhard 2 , Bruce Arey 2 , Zhongyang Cheng 1
1 Materials Research and Education Center, Auburn University, Auburn, Alabama, United States, 2 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractThe magnetostrictive nanobar and its array were recently induced as a high performance biosensor platform. In this paper, we report the fabrication, microstructure, and composition of magnetostrictive nanobars based on Fe-B. The nanobars were synthesized using a template-based electrochemical deposition method. The composition and microstructure, which are directly related to the performance of the nanobars, of the Fe-B nanobar were determined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray photonelectron spectroscopy (XPS) as well as Auger electron spectroscopy (AES). Morphologically, nanobars are featured by very flat top and smooth cylindrical surface, which are critical factors for obtaining high performance as sensor platform. Structurally, XRD and electron diffraction reveal that the Fe-B nanobar is amorphous. AES analysis indicates that the nanobar shows no significant compositional variation along the length direction. HRTEM reveals that the nanobars were covered by an oxidization layer of a typical thickness of ~ 10 nm. It is believed that this oxidation layer is related to the passivation of nanobars in air. High temperature annealing and subsequent structural and compositional analysis indicate that the Fe-B nanobars possess a good thermal stability.
9:00 PM - P9.15
The Evolution of 'Inversion Symmetry Feature' During the Magnetisation Reversal of Array of Ni Nanobars: A 3-D Micromagnetic Study.
Prabeer Barpanda 1
1 Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States
Show Abstract9:00 PM - P9.16
Exchange Bias and Coupling Effects in Superconducting/Ferromagnetic Nanostructured Systems
Elena Navarro 1 , Yves Huttel 2 , María Vélez 4 , Alejandro Pérez-Junquera 4 , Nuria Nuñez 1 , Alfonso Cebollada 3 , José Igancio Martín 4 , José María Alameda 4 , José Luis Vicent 1
1 Física de Materiales, Universidad Complutense, Madrid Spain, 2 Instituto de Ciencia de Materiales de Madrid, ICMM-CSIC, Madrid Spain, 4 Departamento de Física, Facultad de Ciencias, Universidad de Oviedo, Oviedo Spain, 3 Instituto de Microelectrónica de Madrid, IMM-CNM-CSIC, Madrid Spain
Show AbstractCoupling effects in nanostructured superconducting/magnetic systems is one of the most relevant topics in applied as well as basic research in the realm of nanomagnets. In this work, we will present the study of the magnetic behavior of a system made of nanoislands of (110) Fe single-crystals capped with very thin Cr layers and their competition with Nb superconducting films grown on top. Details about the fabrication, structure, morphology and magnetic properties of these systems can be found elsewhere (1).The Nb/Cr/Fe system shows an interplay between the superconducting and the magnetic properties that strongly depends on the exchange bias behavior induced by the Fe nanoisland morphology in the Cr/Fe nanostructures. Exchange bias is not observed in the case of continuous trilayers of Nb/Cr/Fe. Hysteresis loops of Nb/Cr/Fe nanostructures show increasing exchange bias fields with decreasing nanoisland Fe sizes. On the other hand, recent results (2) show that the magnetic coupling between islands depends on the type of capping and the island sizes. The superconducting properties of the Nb films are strongly modified by the coupling and exchange bias effects. The main result is that samples with larger exchange bias fields induce lower superconducting critical temperatures. (1) E. Navarro, Y. Huttel, C. Clavero, A. Cebollada and G. Armelles, Phys. Rev. B69, 224419 (2004).(2) E. Navarro, Y. Huttel, C. Clavero, G. Armelles, and A. Cebollada. Appl. Phys. Lett. 84, 2139 (2004).
9:00 PM - P9.17
Magnetic Switching in Ni Nanowires Sandwiched between Bulk Superconductors.
Nitesh Kumar 1 , Mingliang Tian 1 , Moses Chan 1
1 Center for Nanoscale Science and Department of Physics, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractMagnetic Ni nanowires with diameter 40nm and length 6µm were fabricated by template-based electrochemical deposition in porous polycarbonate membranes. Electrical transport measurements were performed on Ni nanowires sandwiched between bulk superconducting electrodes forming a Superconductor /Ferromagnet /Superconductor hybrid system. Sharp jumps were observed in magnetoresistance (MR) hysteresis loop measured for an array of Ni nanowires sandwiched between Sn electrodes. These jumps or magnetic switching are only seen in the magnetic field regime where Sn electrodes are in superconducting state. MR hysteresis loops were measured with the magnetic field directions parallel and perpendicular to the axis of nanowires. Both the directions of magnetic field showed the pronounced jumps differing only in the onset magnetic field values. MR measurements also showed a strong and non-monotonic excitation current dependence. The observed phenomenon appears to be related to the spin mismatch at the S/F interface with superconducting Sn electrodes favoring an anti-parallel spin alignment as compared to parallel spin alignment of ferromagnetic Ni nanowires. Current measurements are being extended to perform MR studies on single Ni nanowire with superconducting electrodes using Focused Ion Beam technique. Also, experiments are undergoing to make in-situ superconducting contacts to Ni nanowires. The observed magnetic switching behavior from the interplay of incompatible spin orders across the nanoscale S/F interface promises to have great potential in future spintronics applications.
9:00 PM - P9.19
Manipulating Kondo Temperature via Single Molecule Switching.
Violeta Iancu 1 , Aparna Deshpande 1 , Saw Hla 1
1 Physics and Astronomy, Ohio University, Athens, Ohio, United States
Show Abstract9:00 PM - P9.2
High-throughput Investigation of Exchange Coupling Interaction in Soft/Hard Magnetic Bilayer Systems for Development of Nanocomposite Magnets.
Antonio Zambano 1 , H. Oguchi 1 , I. Takeuchi 1 , S. Lofland 2 , D. Josell 3 , L. Bendersky 3 , J. Liu 4
1 Department of Materials Science & Engineering and Center for Superconductivity Research, University of Maryland, College Park, Maryland, United States, 2 Department of Physics and Astronomy, Rowan University, Glassboro, New Jersey, United States, 3 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 4 Department of Physics, University of Texas , Arlington, Texas, United States
Show AbstractIn order to fabricate exchanged coupled hard/soft phase nanocomposite magnets with high maximum energy products, we need to identify the parameters that govern the exchange interaction. To this end, we have performed high-throughput experiments designed to delineate subtle variations of the exchange coupling behavior using a series of thin film bilayers. We have characterized the exchange coupling interaction through two quantities: the coupling length (λ) and the nucleation field (HN). We studied the experimental variations of these quantities on various magnetic parameters, thickness of the soft layer (ts), and interface conditions in thin film libraries of CoPt/(Fe, Co or Ni) and SmCo/(Fe, Co or Ni) bilayers. We have used the model proposed by T. Leineweber et al.1 to fit the experimental results in order to understand the dependence of the nucleation field HN (as a function of ts) on exchange stiffness (A), saturation magnetization (M), and anisotropy (K) of both soft and hard layers. The trend found indicates that the dominant factors determining λ and HN are the hard layer magnetic constants and M of the soft layer. HN and λ display a direct correlation with the domain wall width of the hard layer and has an anticorrelation with M of the soft layers. We will discuss the role played by other parameters on exchange coupling interaction. The results allow us to predict the behavior of coupled hard/soft magnetic layers in general.This work is supported by ONR MURI N00014-05-1-0497.[1] T. Leineweber and H. Kronmüller, J. Mag. Mag. Mat. 176, 145 (1997).
9:00 PM - P9.20
Single Molecule Investigations of Ferrocene with a Scanning Tunneling Microscope: Decompositional and Incommensurate Growth Behavior.
Natalya Pertaya 1 , Kai Braun 1 , Violeta Iancu 1 , Karl Rieder 2 , Saw Hla 1
1 Physics & Astronomy, Ohio University, Athens, Ohio, United States, 2 Institute for Experimental Physics, Freie Universitaet Berlin, Berlin Germany
Show AbstractThe discovery of Ferrocene Fe(C5H5)2 in 1951 and its structural elucidation by two separate research groups in the following year marked the birth of contemporary organometallic chemistry [1]. Metallocenes are composed of a metal atom in between two planar aromatic ligands. Their application as catalysts and organometallic polymers with magnetic properties has received considerable interest over the past two decades. In view of the development of molecular electronics these molecules are expected to exhibit unique properties e.g. by use of magnetic atoms to exploit spindependent effects or for the production of metal-molecule layers. Here, we investigate ferrocene adsorbed on two surfaces, Ag(111) at room temperature [2] and Au(111) at liquid helium temperature [3], in ultra-high-vacuum environment. Deviating from the common growth mode of molecular films of organic molecules where the adsorbates remain intact, we observe an essentially different growth behavior for metallocenes with a low temperature scanning tunneling microscope on Au(111) surface. On this surface, ferrocene molecules adsorb dissociatively and form a two-layer structure. The toplayer unit cell is composed of two tilted cyclopentadienyl rings, while the first layer consists of the remaining fragments. Surprisingly a four-fold symmetry is observed for the top layer while the first layer displays threefold symmetry elements. It is this symmetry mismatch, which induces an incommensurability between these layers in all except one surface direction. The toplayer is weakly bonded and has an antiferromagnetic groundstate as calculated by local spin density functional approximation.[1] E.O. Fischer and G. Wilkinson, Nobel Prize in Chemistry in 1973.[2] N. Pertaya, Ph.D. thesis, Freie Universitaet Berlin, Germany, 2004.[3] K.-F. Braun, V. Iancu, N. Pertaya, K.-H. Rieder, S.-W. Hla, Phys. Rev. Lett. (2006) in press.
9:00 PM - P9.21
Electronic and Structural Properties of Self-assembled Magnetic Molecules.
Gayani Perera 1 , Violeta Iancu 1 , Saw-Wai Hla 1
1 Department of Physics & Astronomy, Ohio Univeristy, Athens, Ohio, United States
Show Abstract9:00 PM - P9.23
Synthesis, Structure and Magnetic Behaviour of Manganese(II) Selenide/Selenolate Cluster Complexes
Andreas Eichhofer 1 , Dieter Fenske 1 , Raghavan Viswanath 1 , Paul Wood 2
1 Institute of Nanotechnology, Forschungszentrum Karlsruhe, Eggenstein-Leopoldshafen Germany, 2 University Chemical Laboratory, University of Cambridge, Cambridge UK United Kingdom
Show Abstract9:00 PM - P9.24
Electronic Structure of the Molecule-Based Room Temperature Magnet V(TCNE)2.
M. de Jong 1 , C. Tengstedt 2 , A. Kanciurzewska 2 , E. Carlegrim 2 , M. Fahlman 2
1 Department of Physics (IFM), Linköping University, Linköping Sweden, 2 Department of Science and Technology (ITN), Linköping University, Linköping Sweden
Show AbstractMetal-tetracyanoethylene complexes, denoted M(TCNE)x where M is e.g. V, Mn, Fe, Cr or a mixture of those metals, form an interesting class of prototype molecule-based magnets in which a significant fraction of the ordered spins resides in p(π)-orbitals, in contrast to the d and f spins encountered in conventional, inorganic magnets. In addition, these complexes are generally amorphous materials with spero(speri)magnetic properties, leading to spin glass behavior or random anisotropy. From a technological point of view, molecule-based magnets offer many potential advantages, since their properties can be modulated via chemical routes, they are lighter, more flexible, and much less energy intensive to produce than metal or ceramic magnets, and insulating or semiconducting behavior can be obtained. V(TCNE)2 is an especially interesting compound since it features magnetic ordering temperatures well above room temperature. Nevertheless, the electronic structure has long remained unknown, since characterisation has been hampered by the extreme air sensitivity of the material. We have recently developed a thin film deposition method based on chemical vapor deposition (CVD) in UHV that enables in-situ analysis with surface sensitive methods such as photoelectron spectroscopy (PES), resonant photoemission (RPE), and x-ray absorption spectroscopy (XAS). Room temperature spin ordering in the V(TCNE)2 thin films is confirmed by x-ray magnetic circular dichroism spectra recorded at the V L2,3-edge. A combination of PES and RPE measured at the V L3-edge shows that the highest occupied band has strong V(3d)-character. Evidence of V(3d) and TCNE-π (π*) orbital overlap contained in RPE spectra indicates that strong bonding occurs between the vanadium ion and the TCNE molecules, which is supported by the interpretation of the V L-edge XAS spectra using atomic multiplet calculations.
9:00 PM - P9.3
Interface Morphology of Metallic Mutilayers by Means of MBE Simulation.
Kazuhito Shintani 1 , Yuichi Yano 1 , Yusuke Kometani 1 , Takaaki Nakajima 1
1 Department of Mechanical Engineering and Intelligent Systems , University of Electro-Communications, Chofu, Tokyo, Japan
Show Abstract9:00 PM - P9.4
Development of Ni-based Epitaxial Electro-magnetic Nanostructures and Hybrid Systems.
Akifumi Matsuda 1 , Masayasu Kasahara 1 , Takahiro Watanabe 1 , Wakana Hara 1 , Sei Otaka 1 , Kouji Koyama 2 , Mamoru Yoshimoto 1
1 Department of Innovative and Engineered Materials, Tokyo Institute of Technology, Yokohama, Kanagawa, Japan, 2 CG Laboratory, Namiki Precision Jewel Co., Ltd., Adachi, Tokyo, Japan
Show AbstractThe epitaxially grown metallic films can induce unique electronic or magnetic properties and also enhance their advantages which are undoubtedly important for the development of many expected applications such as ultra-high density magnetic recording devices with giant magneto-resistance (GMR), magnetic random access memory (MRAM) due to tunnel magneto-resistance (TMR) and other SPINTONICS devices by utilizing their crystallographic anisotropy. These devices may have structures quite sensitive to the growth conditions, nanowires and stacked layers for instance, however conventional techniques such like thermal evaporation and magnetron sputtering require relatively high substrate temperature that may cause surface roughening and interface diffusion result in undesirable electron scattering. Here we report a newly developed low-temperature method to prepare epitaxial hybrid electro-magnetic nanostructures and systems of Ni matrix by conbination of LaserMBE and hydrogen reduction of transition metal oxides. We have grown both [NiO(111)/ZnO(0001)/NiO(111)/sapphire] or [NiO(111)/α-Al2O3(0001)/NiO(111)/sapphire] epitaxially stacked layers and self-assembly formed periodic arrays of epitaxial nanowires and nanogrooves by LaserMBE on ultrasmooth sapphire (0001) substrates with atomic steps of 0.2 nm in height and atomically flat terraces of 50-100 nm in width. The samples were then annealed for an hour in hydrogen gas ambient, to reduce whole antiferromagnetic NiO into ferromagnetic Ni metal and found that the epitaxy remains after the complete reduction into Ni(111); we named this unique epitaxy technique Metal Oxide-Reduction-Epitaxy, "the MORE method." The MORE method has a gaseous process so that nano structured ferromagnetic Ni(111) certainly remained their topographies through the procedure when this technique was applied to oxide nanostructures. Characterizations were made by ex-situ X-ray diffraction (XRD) and atomic force microscopy (AFM) for the epitaxy and surface morphologiies of nano-materials, respectively. Further detailed analyses of interfaces were carried out by transmission electron microscope (TEM). Further experimentals are conducted for magneto-electronic characterizations for above mentioned ferromagnetic-metal/semiconductor hybrid nano-materials.
9:00 PM - P9.5
Heterostructured Oxide Spin Devices using Tunable Ferromagnetic Semiconductor of High TC Spinel Fe3-xMnxO4 Films
Tomoji Kawai 1 , Hidekazu Tanaka 1 , Issei Satoh 1 , Mizue Ishikawa 1 , Yoshihiko Yanagisawa 1 , Luca Pellegrino 2
1 ISIR-Sanken , Osaka University, Osaka Japan, 2 , CNR-INFM-Lamia & Genova Univ., Genova Italy
Show AbstractSpine ferrites are attractive materials for spintronics due to their High TC, but are usually insulators or a metallic magnetite whose carriers cannot be controlled. We propose a new tuneable ferromagnetic oxide semiconductor, Fe3-xMnxO4 (FMO) with High TC (>600K), and report construction of their functional oxide heterostructures of ferromagnetic Field Effect Transistor, Ferromagnetic Schottky diode, and Ferromagnetic submicron-dot. Epitaxial Fe3-xMnxO4 (FMO:x=0 to 1.0) thin films were deposited on MgO (001) substrates by Pulsed Laser Deposition[1]. Anomalous Hall Effect measurements revealed its polarized carrier concentration is systematically tuned from 8.2×1021/cm3 to 7.3×1020/cm3 by changing x ratio from 0 to 0.5,with keeping carrier mobility of 0.2 cm2/Vs at 300 K. A valence band and Mn:2p/Fe:2p core level spectrum investigated by X-ray photoemission spectroscopy indicated that Mn2+ ion substituted in A site systematically reduce density of state at EF to preserve charge neutrality without disturbing conduction path of Fe ion network. These tuneable electrical properties as a ferromagnetic semiconductor enable us to construct to following advanced spin oxide heterostructures. ○FMO (x=0.5) Ferromagnetic–FET with ferroelectric Pb(Zr,Ti)O3 gate show systematic channel resistance modulation via carrier modulation reflecting ferroelectric hysteresis for the first time in Spinel oxides family.○FMO/Nb-SrTiO3 Schottky diode showed good rectifying property, and their magnetic field dependence indicated high spin polarization of 0.8 at 100K from thermionic emission theory [2]. We will also discuss room temperature spin polarization.○Charge accumulation was observed within the isolated FMO submicron dot fabricated by Mo-Nano mask oxide lithography[3], whereas no accumulation was observed in that connected to outer area via nano-bridge whose width of 70nm.Hetero-and Nano-structuring of spinel FMO films can lead to the realization of advanced spintronic devices such as oxide Magnetic Random Access Memory controlled by with electric field over room temperature.[1] M. Ishikawa et al. Appl. Phys. Lett. 86 (2005) 222504[2] M. Ziese et al., Phys. Rev. B 71, 180406 (2005).[3] L. Pellegrino et al, in submission.
9:00 PM - P9.6
Tin Oxide Based Transparent Ferromagnetic Semiconductor Thin Films by Spray Pyrolysis.
Subhash Kashyap 1 , K. Gopinadhan 1 , Sujeet Chaudhary 1 , Dinesh Pandya 1
1 Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110 016 India
Show AbstractSpintronics refers to the study of spin behavior of charge carriers in a material/device that specifically exploits the spin properties instead of or in addition to charge of the carriers. A new potential application in spintronics will come into existence if room temperature ferromagnetism (RTFM) is somehow induced in oxide semiconductors like SnO_2, ZnO, TiO_2, etc. In case of ZnO, though the ferromagnetic state induced by transition metal (TM) doping is reported, the experimental results in (Mn,Co):ZnO bulk and thin films, published so far, are diverse regarding the presence/origin of RTFM. The studies on SnO_2 have so far indicated that the Curie temperature is well above room temperature (RT); the samples possess a maximum ferromagnetic moment of ~7.8μ_B/Co-ion, or ~0.133μ_B/Co; and that there is absence of ferromagnetic ordering, etc. In order to understand the RTFM in TM-doped oxide systems, and to obtain transparent ferromagnetic semiconductors, we have been investigating spray-deposited thin films of SnO_2, doped with Mn and Co. The choice of SnO_2 is motivated by the fact that the electron concentration in it can be easily varied and the host matrix exhibits visible transparency. The carrier mediated magnetic interaction has important consequences in new applications; the carrier concentration can be tuned electrically also, thereby resulting in a change in magnetic moment of the nano-magnets formed. The Mn- and Co-doped SnO_2 thin films have been spray-deposited using aqueous solutions of soluble salts of Mn, Co and Sn on quartz substrates. The films have greater than 80% visible transparency. The glancing angle X-ray diffractograms of SnO_2:TM films indicate that Mn/Co is incorporated in the phase pure SnO_2. Also, the magnetization studies indicate that for the 7.5 and 10 a/o Mn and 5-10 a/o Co, the films show RTFM, showing a maximum magnetic moment at 10 a/o. The film with x ≥ 12.5 a/o shows a paramagnetic behavior indicating that the FM is not due to any Mn/Co cluster formation. The disappearance of ferromagnetism beyond a Mn-concentration of 10 a/o may be due to close proximity of antiferromagnetic Mn-atoms, which reduces or cancels the spin ordering. In the case of SnO_2:Co thin films, the observed anomalous Hall effect has established that the electrons are spin-polarized by the magnetic Co entities. The systematic variation of saturation magnetic moment, electron concentration and optical blue shift are employed to infer a mechanism for the magnetic ordering in these films. The absence of in-gap conductivity implies that cobalt does not introduce any mid-gap levels as expected from its partially filled 3d-levels. These films show extrinsic semiconducting behavior with carrier concentration of ~5 x 10^19 cm^-3 and have a grain size of 10-25 nm. Efforts are being made to understand the mechanism of magnetic ordering and thereby enhancing the ferromagnetism.
9:00 PM - P9.7
Anomalous Hall Effect in Superparamagnetic Co-(La,Sr)TiO3
Shixiong Zhang 1 , Weiqiang Yu 1 , Sheng-Yu Young 2 , Satish Ogale 1 , Darshan Kundaliya 1 , Sankar Dhar 1 , Sanjay Shinde 1 , Joshua Higgins 1 , Ranjan Sahu 1 , Richard Greene 1 , Lourdes Salamanca-Riba 2 , Thirumalai Venkatesan 1
1 Center for Superconductivity Research, Department of Physics, University of Maryland, College Park, Maryland, United States, 2 Department of Materials Science and Engineering , University of Maryland, College Park, Maryland, United States
Show Abstract9:00 PM - P9.8
Structural and Morphological Characterization ofNanostructured CoFe2O4 Thin Films by Pulsed Laser Deposition.
Mahidanna Rao 1 2 , K. Mohankant 1 2 , K. Sethupathi 1
1 Physics, Indian Institute of Technology, Chennai, TamilNadu, India, 2 Materials Science Research Centre, IITM, Chennai, Tamilnadu, India
Show Abstract9:00 PM - P9.9
The Use of Porous Alumina Matrix for Controlled Growth of Magnetic Nanowires
Andrey Eliseev 1 , Kirill Napolskii 1 , Nikolay Esin 1 , Eugeny Trubitsyn 2 , Alexey Lukashin 1
1 Dept. of Materials Science, Moscow State University, Moscow Russian Federation, 2 Dept. of Chemistry , Moscow State University, Moscow Russian Federation
Show AbstractOne of the most widespread methods of synthesis of nanostructures is preparation of nanocomposites – it allows us to stabilize the particles in chemically inert matrix.One of the promising matrices for preparation of anisotropic nanoparticles is anodic alumina.Anodized alumina is an amorphous aluminum oxide with ordered uniform pore structure. The use of different conditions of synthesis of porous alumina allows us to change pore size and film thicknesses in a wide ranges (pore diameter from 15 nm to 200 nm; thicknesses from 500 nm to 0,5 mm). Such properties make this material extremely attractive as a perfect reactor for synthesis of nanocomposites due to the limitation of reaction zone by the pore walls. An important advantage of this system is the possibility to incorporate any compound by electrochemical methods, which enables simple handling over loading values and, therefore, makes it possible to control the anisotropy parameters of nanostructures.In the frames of present study we investigate the formation of Ni and Co nanoparticles in the porous aluminum oxide with different pore diameters. The composites were prepared by electrochemical metals deposition from water solutions of corresponding metal salts in three-electrode cell. Nanocomposites were characterized by TEM, ED, HRSEM, BET, XRD, SPM, SANS and magnetic measurements. It was showed that particles’ shape and size are in good agreement with that of the pores. Besides, the influence of nanoparticles morphology enables to predetermine magnetic properties of nanocomposite. It was found that the anisotropy factor of nanowires attain the value of about 1000. Such wires represent high coercive force up to 650 Oe (at 300K). Thus such films may serve as a test system for information storage.This work is supported by RFBR (03-03-32182) and INTAS (01-204).
P10: Poster Session: Magnetic Nanoparticles
Session Chairs
John Chapman
Jurgen Fassbender
Caroline Ross
Friday AM, December 01, 2006
Exhibition Hall D (Hynes)
9:00 PM - P10.10
One-Pot Synthesis and Characterization of Size-controllable Magnetite Nanoparticles
Zhichuan Xu 1 , Yanglong Hou 1 , Shouheng Sun 1
1 Department of Chemistry, Brown University, Providence, Rhode Island, United States
Show AbstractWe report an improved, yet, very simple one-pot synthesis of Fe3O4 nanoparticles with sized tunable from 6-22 nm. The Fe3O¬¬4 nanoparticles were prepared by the decomposition of iron acetylacetonate [Fe(acac)3] in the presence of oleic acid and oleylamine, in which oleylamine served also as the solvent and no reducing agent was required. The sizes of the particles were controlled by tailoring the molar ratio of oleic acid to oleylamine and reaction conditions. In addition, magnetite nanocubes were also obtained through tuning the reaction condition such as molar ratio of precursor to surfactants, heating rate, and reaction temperature.This one-pot reaction can be readily extended to the synthesis of other iron oxide nanoparticle materials. For example, by adding samarium acetylacetonate into the reaction mixture of Fe(acac)3 and oleylamine, monodisperse samarium ferrite nanoparticles were separated. The iron oxide nanoparticles are readily functionalized with hydrophilic surfactants for potential biomedical applications while the samarium ferrite nanoparticles will serve as excellent precursors for fabrication of high performance permanent magnetic nanocomposites.
9:00 PM - P10.11
Magnetic Domains Defined in Boundaries and Cores of Iron Oxide Nanoparticles.
Maria Castellanos Roman 1 , Beatriz Gomez L 1 , Jaime Santoyo Salazar 2
1 Facultad de Quimica, Universidad Nacional Autonoma de Mexico, Mexico DF, DF, Mexico, 2 Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Mexico, DF, Mexico
Show AbstractRecent advances in new generation nanotechnology, have helped to improve the field application of magnetic materials based on Magnetite (Fe3O4) in ferrofluids which have been widely used in position sensing for avionics, robotics, machine tools, and automotives(1) with reproducibility and fast response ability. In this work, Fe3O4 nanoparticles were obtained by a precipitation route in alkaline medium; and taking into account the relationship between processing, structure and nanometric size particle, the polycristalline products were characterized. A structural analysis done by X-ray diffraction (XRD) and a scanning probe microscopy (SPM) in Tapping mode showed nanoparticles in a range of 30nm. Finally, through a powerful magnetic force microscopy (MFM) analysis of core and border of Fe3O4 nanoparticles, visible and well defined magnetic domains were observed. Results showed the field and directions of wall domains, like ribbons, in an order of 4nm. 3D images allowed to identify positive and negative magnetic fields and the sequence of domains in different scanned areas.
9:00 PM - P10.12
Size Controlled Synthesis of Monodisperse Iron Oxide Nanoparticles by Controlling Nucleation and Growth Time.
Yun-Tack Lee 1 2 , Ki-Bum Kim 2 , Kyoungja Woo 1
1 Nano-Materials Research Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 School of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show Abstract9:00 PM - P10.13
Shape-Selective Protein-Templated Synthesis of Superparamagnetic Magnetite Nanocrystals.
Tanya Prozorov 1 2 , Surya Mallapragada 1 2 , Balaji Narasimhan 1 2 , Lijun Wang 3 , Pierre Palo 3 , Marit Nilsen-Hamilton 3 , Timothy Williams 3 , Dennis Bazylinski 3 , Ruslan Prozorov 4 2 , Paul Canfield 4 2
1 Department of Chemical and Biological Engineering , Iowa State University , Ames, Iowa, United States, 2 Ames Laboratory, Ames Laboratory, Ames, Iowa, United States, 3 Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, Iowa, United States, 4 Department of Physics and Astronomy, Iowa State University, Ames, Iowa, United States
Show AbstractSeveral proteins were tested for the shape-selective synthesis of 20-30nm magnetite nanocrystals. Magnetite nanocrystals were synthesized in the presence of a biomineralization protein involved in the biomineralization of bacterial magnetosomes, recombinant Mms6; the mammalian iron-storage protein, ferritin; and two proteins not known to bind iron, uterocalin Lcn2, and bovine serum albumin. In order to slow down the diffusion rates of the reagents and mimic the conditions at which magnetite nanocrystals are formed in magnetotactic bacteria, magnetite synthesis was performed in an aqueous polymeric gel. Both the native and refolded recombinant Mms6 proteins facilitated formation of ~30 nm single-domain, uniform isomorphic magnetite nanocrystals in solution, as verified by transmission electron microscopy analysis and magnetization measurements. The nanocrystals formed in the presence of ferritin, Lcn2, and bovine serum albumin did not exhibit the uniform sizes and shapes observed for those produced in the presence of Mms6. Mms6-derived magnetite nanoparticles exhibited the highest blocking temperature and the largest magnetization values above the blocking temperature, as well as the largest magnetic susceptibility compared to those of the nanomaterials synthesized with other proteins. The latter is indicative of a substantial effective magnetic moment per particle, which is consistent with the presence of magnetite with a well-defined crystalline structure. The combination of electron microscopy analysis and magnetic measurements confirm our hypothesis that Mms6 promotes the shape-selective formation of uniform superparamagnetic nanocrystals. This provides a unique bioinspired route for synthesis of uniform magnetite nanocrystals.
9:00 PM - P10.14
Surface Modified Iron Oxide Nanoparticles: A Versatile Tool for Diagnosis and Therapy.
Dattatri Nagesha 1 2 , Rishikesh Sawant 3 , Shane Lloyd 1 , Evin Gultepe 1 2 , Vladimir Torchilin 3 , Srinivas Sridhar 1 2
1 Electronics Material Research Institute, Northeastern University, Boston, Massachusetts, United States, 2 Physics, Northeastern University, Boston, Massachusetts, United States, 3 Pharmaceutical Sciences, Northeastern University, Boston, Massachusetts, United States
Show Abstract9:00 PM - P10.15
Dumbbell-like Composite Nanoparticles: Chemical Synthesis and Catalytic Applications
Chao Wang 1 2 , Chengmin Shen 1 , Hideo Daimon 3 , Shouheng Sun 1
1 Division of Engineering, Brown University, Providence, Rhode Island, United States, 2 Department of Chemistry, Brown University, Providence, Rhode Island, United States, 3 Division of Development & Technology, Hitachi Maxell, Ltd., Tsukubamirai, Ibaraki, Japan
Show AbstractDumbbell-like Au-Fe3O4, Ag-Fe3O4, Pt-Fe3O4 and Pd-Fe3O4 nanoparticles are synthesized by epitaxial growth of Fe3O4 on noble metal nanoparticle seeds. The metal seeds are synthesized at first via solution phase reduction of noble metal salt. Fe3O4 nanoparticles are grown on the seeds by thermal decomposition of Fe(CO)5 in organic solvent followed by air oxidation. The size of the metal and Fe3O4 particles in these dumbbell structures can be well controlled (from 2 nm to 20 nm). Moreover, the shape of the dumbbell nanoparticles can also be controlled by varying the reaction condition (both spherical and cubic Pt-Fe3O4 dumbbell nanoparticles are synthesized, for example). These dumbbell nanoparticles are superparamagnetic at room temperature, and also show plasmonic absorption (from Au or Ag). More important, compared to the single-component noble metal nanoparticles, the dumbbell particles show enhanced catalytic properties, like Pt-Fe3O4 for oxygen reduction and methanol oxidation in the fuel cell, as well as Au-Fe3O4 for the growth of silicon nanowires.
9:00 PM - P10.16
The Heating Effects of Dextran Coated Iron Oxides.
Qi Zeng 1 , Ian Baker 1
1 Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, United States
Show AbstractThe magnetic behavior and the heating effects of three different Dextran-coated iron oxide nanoparticles were investigated with respect to their possible application for magnetic hyperthermia treatments. The crystallite size was determined via X-ray diffraction and TEM, while the coated particle size (iron oxide + Dextran) was measured using a SEM. The quasi-static magnetic properties of the particles either dispersed in water, in an immobilized state, or in powder form were measured using a VSM. Alternating magnetic field strengths in the range of 75 -210 Oe and frequencies of 10-250 kHz were applied, and a nearly linear relationship was found between the square of the applied field and the specific (heat) absorption rate, SAR, and between the frequency and SAR. The largest SAR, of 227 W/g, was found for 15-20 nm dia. Fe2O3 nanoparticles under an applied field of 210 Oe at a frequency of 250 kHz. The heating behavior will be discussed in relation to the magnetic behavior of the nanoparticles and the applied fields.Research sponsored by NIST grant 60NANB2D0120.
9:00 PM - P10.17
Synthesis and Magnetic Properties of Pr0.57Ca0.43MnO3 Nanoparticles.
Zhenqing Wang 1 , Junming Liu 1 , Zhifeng Ren 2
1 Department of Physics, Nanjing University, Nanjing China, 2 Department of Physics, Boston College, Boston, Massachusetts, United States
Show AbstractIn this paper, Pr0.57Ca0.43MnO3 nanoparticles with an average grain size of 18.5 nm have been synthesized using hydrothermal method combined with post annealing and characterized using x-ray diffraction, high resolution transmission electron microscope, and superconducting quantum interface device magnetometer. The results show that Pr1-xCaxMnO3 compound is difficult to be synthesized using hyrdrothermal method under 240oC. The Pr0.57Ca0.43MnO3 nanoparticles obtained from annealing the hydrothermal products at 900oC for 2h possess an orthorhombic perovskite structure with cell constants the same as those of Pr0.6Sr0.4MnO3. Magnetic characterization reveals that antiferromagnetic and charge order transitions in the Pr0.57Ca0.43MnO3 bulk materials completely disappear in the present nanoparticles, and that a transition from paramagnetic to ferromagnetic state occurs at around 110K. The peak in the zero field cooled (ZFC) magnetization indicates that Pr0.57Ca0.43MnO3 nanoparticles exhibits a spin freezing behavior.
9:00 PM - P10.18
AC-susceptibility Measurements of the Superparamagnetic Relaxation in Systems of Ni1-xZnxFe2O4 Nanoparticles.
Antony Adair 1 , José Elizalde Galindo 1 , Cristian Botez 1 , Verónica Corral Flores 2 , Dario Bueno Baques 2 , Luis Fuentes Cobas 2 , José Matutes-Aquino 2
1 Physics, University of Texas - El Paso, El Paso, Texas, United States, 2 , Centro de Investigación en Materials Avanzados, Chihuahua Mexico
Show Abstract9:00 PM - P10.2
Tuning Crystal Structure and Magnetics at the Nanometer Scale – First Experiment of Forming Ordered FePt Nanomagnets in Gas Phase
Jiao-Ming Qiu 1 , Stuart McKernan 2 , Jian-Ping Wang 1
1 The Center for Micromagnetics and Information Technologies (MINT) and Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota, United States, 2 Characterization Facility, Institute of Technology, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractNanocrystals are generally prepared using colloidal methods based on chemical reduction of various kinds of compound precursors. Their crystal structures and physical properties are therefore influenced by many different parameters of the solution. For surface related properties, the effects of adsorbates are sometimes useful but very often they may cover up the intrinsic performance of surface atoms. For magnetic materials, crystal structure control is very important not only because the arrangement of bulk atoms determines the magnetic properties but also because atoms on different crystal surfaces have different contribution. Here we report a preparation method that can tune the crystal structure and magnetic properties of nanocrystals and at the same time provide materials without surface adsorbates. In this method gas phase aggregation is used to generate nanocrystals. Crystal structure control is achieved by directly manipulating the energy carried by nucleating atoms and growing species using magnetron plasma as the adjustable energy source. At three different densities of plasma, FePt nanocrystals with three different kinds of crystal structures, A1 icosahedron, A1 octahedron and L10 octahedron were prepared, respectively. High-resolution TEM images clearly show the different arrangements of atoms and magnetic measurements reveal that they have very different magnetic performance. These materials can be used as different types of nanoscale magnets having the same chemical composition. The potential applications of them are magnetic storage media, magnetic sensor and labeling devices, as well as that for biomedical applications. The technique reported here can be easily extended to other magnetic as well as non-magnetic nanocrystal fabrication thus to provide a general platform for technological and fundamental study at the nanometer scale.
9:00 PM - P10.20
Synthesis of a Magnetic-dielectric YIG@BaTiO3 Composite via Hydrothermal Processing.
Shin-Wei Lin 1 , Mean-Jue Tung 1
1 Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu Taiwan
Show AbstractYIG@BaTiO3 composite was synthesized by a sequential process involving the formation of TiO2 by sol-gel reaction and a subsequent hydrothermal transformation from TiO2 to BaTiO3. TiO2 layer was coated on YIG particle via sol-gel reaction which comprised hydrolysis and condensation reaction of titanium n-butoxide. The pH value of the solution was precisely controlled to ensure that YIG particles could be well dispersed in the solution and the concentrations of TBOT and H2O were adjusted to obtain variant thickness of TiO2 layer. Nano-sized BaTiO3 coating on YIG was achieved by a hydrothermal conversion of the TiO2 shell layer. BaTiO3 shell layer was synthesized in an autoclave at 240°C for 12 hours and the concentration ratio of [Ba]/[Ti] was 1.6. Phases and morphology of the composite are identified by X-ray diffraction and SEM, respectively. Magnetic properties of YIG@BaTiO3 composite were investigated by vibrating sample magnetometer. Coercivity of YIG@BaTiO3 composites with different composition were not affected but the saturated magnetization dropped down with increasing of the volume ratio of BaTiO3. Permittivity of YIG was raised by coating of BaTiO3 layer and was varied from 6 to 40 and 70 by tuning the volume ratio of BaTiO3 in the composite. The mechanism of the formation of YIG@BaTiO3 composite was also discussed in the article.
9:00 PM - P10.21
High Density Magnetic Co Nanodot Array FabricationUsing Diblock Copolymer Template and Self-assembled Monolayer.
Su-Jin Kim 1 , Wan-Joo Maeng 1 , Han-Bo-Ram Lee 1 , Dae-Ho Park 1 , Byeong-Hyeok Sohn 2 , Hyung-Jun Kim 1
1 Dep. of Materials Science and Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of), 2 Department of Chemistry, Seoul National University, Seoul Korea (the Republic of)
Show Abstract For high density magnetic recording media over 100 Gb/in2, the fabrication of well ordered nanometer scale magnet dot array is required. Especially, embedded magnetic nanodot has benefits of higher thermal stability. In this study, instead of random copolymer, a self-assembled monolayer (SAM), MPTS (3-(p-methoxyphenyl)propyltrichlorosilane), was employed to produce hexagonal array of perpendicularly oriented cylindrical nanodomains made from PS-b-PMMA (polystyrene-b-polymethylmetacrylate) diblock copolymer on SiO2. Well ordered hexagonal nanohole array was fabricated in PS by proper annealing and selective removing process of PMMA. Using this nanotemplate, metal nanodot array including Au or Co was easily fabricated using lift off technique and physical vapor deposition (PVD). For embedded Co nanodot array, the nanohole pattern of PS was transferred to SiO2 underlayer by regular dry etching technique. Co was deposited by novel plasma enhanced atomic layer deposition (PE-ALD) as well as PVD for fabrication of magnetic Co nanodot array. The process using lift-off and selective deposition as well as the topological/chemical prepattering for better ordering will be presented along with magnetic property characterization results using magnetic force microscopy (MFM).
9:00 PM - P10.22
Magnetic Property of α–Fe Nanoparticles Prepared by Solventless Thermal Decomposition Method.
Young Chul Han 1 , Young Soo Kang 1 , Young Hwan Kim 1 , Chang Woo Kim 1 , Hyun Gil Cha 1
1 Chemistry, Pukyong National Univ., Pusan Korea (the Republic of)
Show AbstractThis work reports the synthesis and characterization of the soft magnetic α–Fe nanoparticles by solventless thermal decomposition method. The saturation magnetization value of α–Fe nanoparticles is almost equivalent to the bulk Fe powder (Mbulk = 210 emu/g). To make the α–Fe nanocrystal, prepared Fe2+–oleate2 complexes were annealed in pyrex tube at 400 oC for 2 hrs. And they were heated at 700 oC with Ar + H2(4%) mixture gas atmosphere for reduction. After reduction, prepared α-Fe nanoparticles were annealed under vacuum at 1.8×10–5 torr to remove covered surfactants. Magnetic property such as saturation magnetization was measured by vibration sample magnetometer (VSM). And crystallinity and structure of α–Fe nanoparticle were identified by using X–ray powder diffraction (XRD). The shape and size were investigated by transmission electron microscope (TEM) images.
9:00 PM - P10.23
Synthesis and Stabilization of Monodispersed Fe Nanoparticles
Sheng Peng 1 , Chao Wang 1 , Jin Xie 1 , Shouheng Sun 1
1 Department of Chemistry, Brown University, Providence, Rhode Island, United States
Show AbstractMonodispersed iron nanoparticles (NPs) in the size range below 20 nm are in superparamagnetic regime with high magnetic moment, and their stable NP dispersions in various liquid media are predicted to have important applications in bio-separation, bio-sensing, drug delivery and MRI contrast enhancement. Stabilization of Fe NPs against rapid oxidation, however, has not been achieved thus far, limiting their application potentials. Using a simple one-pot synthesis, we are able to produce monodispersed Fe NPs with high magnetic moment density. The nanoparticles are further stabilized by controlled oxidation and formation of crystalline Fe3O4 shell. The core/shell structure Fe/Fe3O4 show dramatic increase in both chemical and dispersion stability. Surface ligand exchange is readily applied to transfer the core/shell NPs from hydrophobic to hydrophilic, forming stable aqueous dispersion of the NPs in PBS. The functionalized NPs are suitable for biomolecule attachment and biomedical applications.
9:00 PM - P10.24
Iron Nanoparticles Embedded in SrRuO3 Thin Films.
Aman Ullah 1 2 , Young Zo Yoo 1 2 , Stanislaw Kolesnik 1 2 , Omar Chmaissem 1 2 , Michael Maxwell 1 , Dennis Brown 1 2 , Bogdan Dabrowski 1 2 , Clyde Kimball 1 2 , Alan Genis 2 3
1 Physics, Northern Illinois University, Dekalb, Illinois, United States, 2 Institute of NanoScience, Engineering and Technology, Northern Illinois University, Dekalb, Illinois, United States, 3 Electrical Engineering , Northern Illinois University, DeKalb, Illinois, United States
Show Abstract9:00 PM - P10.25
Synthesis and Characterizations of Megnetic-Core/ Metal-Shell Nanocomposite Materials
Lingyan Wang 1 , Masatsugu Suzuki 2 , Itsuko Suzuki 2 , Jin Luo 1 , Chuan-Jian Zhong 1
1 Chemistry, State Univ. of New York at Binghamton, Binghamton, New York, United States, 2 Department of Physics, State Univ. of New York at Binghamton, Binghamton, New York, United States
Show AbstractNanoscale magnetic materials have great technological importance in magnetic data storage, chemical/biological sensing as well as catalytic applications. The ability to control the surface chemistry becomes increasingly important for these applications, which also governs the magnetic properties of the nanomaterials. Megnetic-core/metal-shell nanostructured materials derived from magnetic core (i.e. g-Fe2O3, Fe3O4) provide intriguing opportunities for designing the surface chemistry through the metal shells. In this paper, recent results of an investigation of the synthesis of magnetic nanoparticles and their core@shell composite nanoparticles will be described. One example the synthesis involves controlling the reaction temperatures and manipulating the capping agent properties and solution compositions. Iron oxide nanoparticles in the 2-20 nm size range with controllable sizes, shapes, and core-shell compositions are obtained. The iron oxide nanoparticles were used as seeding materials for the reduction of gold precursors to form Fe-oxide@Au core@shell nanoparticles. The resulting core@shell nanocomposites have been characterized using TEM, XRD, XPS, UV-Vis, DCP-AES, and SQUID techniques. While magnetization, remance magnetization, blocking temperature, and susceptibility were found to decrease after coating iron oxide seeds with Au shells, the coercivity was shown to increase with Au coating. The average sizes of the core@shell nanoparticles derived from the magnetic measurements were consistent with data from other characterization methods. The implications of the findings to the design of novel magnetic materials will also be discussed.
9:00 PM - P10.27
Continuous Synthesis of Inorganic Magnetic Nanocomposites by Laser Pyrolysis for Biomedical Applications.
Nathalie Herlin-Boime 1 , Sabino Veintemillas 2 , Yann Leconte 1 , Maria Puerto Morales 2 , Brigitte Bouchet-Fabre 1 , Rocio Costo 2 , Pierre Bonville 1
1 , Commissariat à l'Energie Atomique, Gif sur Yvette cedex France, 2 , Instituto de Ciencia de Materiales de Madrid, madrid Spain
Show AbstractNanocomposite particles made from encapsulation of magnetic nanoparticles in an inorganic matrix have a real interest in biomedicine due to their high resistance against biodegradation compared with nanoparticles encapsulated in an organic matrix and little work has been published concerning such materials. In this work we use the laser pyrolysis method for the preparation of magnetic composites of Fe-based nanoparticles dispersed in silica and carbon. The precursor is an aerosol of a precursor which can be easily used in a safe way. Important advantages of the laser pyrolysis method are the reproducibility, simplicity (one step method) and continuity which allows producing significant amounts of nanoparticles. The short reaction times (ms) involved in the nucleation of the powders insure the nanometric particle size of both the magnetic component and the inorganic matrix. This paper is focused on the synthesis and characterization of the Fe@SiO2 and Fe@C nanopowders generated by laser pyrolysis of ferrocene diluted in toluene and carried to the reaction zone in aerosol form. The silica coating was formed by the addition of tetraethoxysilane (TEOS) to the reactant. The samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), transmission electron microscopy (TEM), specific surface area determination (BET) and magnetic measurements. In the case of Fe@SiO2 the process generates rather homogeneous iron/magnetite particles smaller than 10 nm in diameter surrounded by a SiO2 coating of about 20 nm. In the case Fe@C the process generate iron based magnetic nanoparticles of complex composition smaller than 11 nm surrounded by a graphitic carbon layer of 50 nm. Stable aqueous dispersions at physiological pH were produced for both systems by means of strong oxidation in aqueous solutions, which is a very encouraging result for application in the field of living tissues.
9:00 PM - P10.28
The Effect of Thin Film Matrix on the Structural and Magnetic Properties of Embedded, Self-Assembled Magnetic Particles
Jeremiah Abiade 1 , Alok Gupta 1 , Adero Paige 1 , Dhananjay Kumar 1
1 Mechanical Engineering & Chemical Engineering, North Carolina A&T State University, Greensboro, North Carolina, United States
Show AbstractThe controlled synthesis of nanostructured magnetic particles with uniform size, shape, composition, and preferred orientation is a formidable task. Some techniques have been demonstrated with limited success; however, reproducible processing schemes for heterogeneous magnetic materials are still not satisfactory. In our work, we are using pulsed laser deposition to embed self-assembled, nanostructured magnetic particles in a variety of thin film matrices (oxides, nitrides, nonmagnetic metals, etc.). In this talk, we will discuss the effect of matrix type on the structural characteristics and resultant magnetic properties of the multilayer structures. Results from x-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis along with vibrating sample magnetometer (VSM) data will be presented. The field, temperature, and angular dependence of the magnetic moment have been studied. XRD and TEM analysis confirms the size range of the nanoparticles is 5 – 60 nm. Furthermore, TEM analysis suggests the particles are slightly elongated with their short axis perpendicular to the substrate. In this talk, we will also discuss the effect of lattice mismatch and particle aspect ratio on the crystalline and shape magnetic anisotropy.
9:00 PM - P10.29
Chemical Synthesis and Characterization of SmCo5 and Fe/Co-Doped SmCo5 Hard Magnetic Nanocomposites
Yanglong Hou 1 , Zhichuan Xu 1 , Shouheng Sun 1 , Chuan-Bing Rong 2 , J. Ping Liu 2
1 Department of Chemistry, Brown University, Providence, Rhode Island, United States, 2 Department of Physics, University of Texas at Arlington, Arlington, Texas, United States
Show AbstractSmCo-based alloy materials, especially nanostructured SmCo5 and Sm2Co17, are excellent candidates for high performance permanent magnetic applications. Here we report preparation of hard magnetic SmCo5 phase based on solution phase synthesis and reductive annealing. Samarium cobalt oxides were first produced from solution phase precipitation of Sm-salt and Co-salt by a base. The oxides were then reduced at high temperature (up to 900 oC), giving hard magnetic SmCo5. Similarly, the hard magnetic SmCo5 materials were made by reductive annealing and interface diffusion of the core/shell structured Co@Sm2O3 nanoparticles. Magnetic studies of the SmCo5-based materials show coercivity as high as 8.9 kOe and saturation magnetization up to 58 emu/g. Furthermore, Fe/Co-doped SmCo5 hard magnetic nanocomposites were prepared by doping monodisperse Fe3O4 nanoparticles into the Sm-Co-O matrices followed by reductive annealing. These magnetic composites show enhanced magnetic properties compared to their SmCo5 counterparts with coercivity and magnetization values reaching to 10.3 kOe and 72 emu/g, respectively. The influence of Fe/Sm/Co molar ratio on the magnetic properties of the products was systematically studied. The composite materials produced here can be used to fabricate permanent magnetic nanocomposites with high energy product.
9:00 PM - P10.3
Synthesis of FePt Nanocubes and Their Oriented Self-Assembly
Jaemin Kim 1 , Yanglong Hou 1 , Shouheng Sun 1
1 Chemistry, Brown University, Providence, Rhode Island, United States
Show AbstractMonodisperse FePt nanocubes are chemically synthesized at 205°C by controlling decomposition of Fe(CO)5 and reduction of Pt(acac)2 and addition sequence of oleic acid and oleylamine in organic solvent. Different from the assembly of the sphere-like FePt nanoparticles, which shows 3D-random structure orientation, self-assembly of the FePt nanocubes leads to a superlattice array with each FePt cube exhibiting (100) texture. Thermal annealing converts the chemically disordered fcc FePt to chemically ordered fct FePt and the annealed assembly shows a strong (001) texture in the directions both parallel and perpendicular to the substrate. This shape controlled synthesis and self-assembly offers a promising approach to fabrication of magnetically aligned FePt nanocrystal arrays for high density information storage and high performance permanent magnet applications.
9:00 PM - P10.30
Nanomagnetism and Nonlinear Magneto-optics: Magnetization-induced Second- and Third-harmonic Generation in Co Nanostructures.
Oleg Aktsipetrov 1 , Evgeniya Kim 1 , Tatyana Murzina 1 , Anatoliy Kravets 2
1 Department of Physics, Moscow State University, Moscow Russian Federation, 2 , Institute of Magnetism of National Academy of Sciences of, Kiev Ukraine
Show Abstract9:00 PM - P10.4
Study of L10 ordered FePt nanostructures integrated with silicon
Gopinath Trichy 1 , Honghui Zhou 2 , Jagdish Narayan 1
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractSynthesis and study of magnetic nanostructures has received much attention in recent years owing to its potential use in high-density recording media. In particular the L10-ordered FePt material system has generated much research interest because of its excellent properties such as; high uniaxial magnetocrystalline anisotropy, high coercivity, high saturation magnetization and good chemical stability. The superior magnetic properties of the FePt system arise due to its ordered L10 structure and under equiatomic composition the ordered structure has Fe and Pt atomic planes stacked alternatively along the c-axis. In this study the technique of pulsed laser deposition was used to synthesize epitaxial FePt nanostructures integrated with Si (001) substrates. The nano islands are formed by self-assembly and follow a 3D-Volmer Webber mode of growth. The FePt nanostructures were grown on a Si (001) substrate using TiN as a template. The TiN template was used to control the epitaxy and induce L10 ordering in the FePt nanostructures. X-ray diffraction results showed a strong growth orientation along the [00l] direction i.e. the direction perpendicular to the plane of the film. The X-ray diffraction pattern also showed the existence of the FePt (001) superlattice peak that indicates the presence of L10 ordering. Crosssectional TEM analysis showed that the islands are well separated and have a thickness of about 5 nm. The SAD (selected area diffraction) pattern in a <110> zone axis showed the following epitaxial relationship; FePt(001)T<001>//TiN(100)<001>//Si(100)<001>. The SAD pattern also showed additional superlattice spots of FePt that confirm L10 ordering. Using plan view TEM analysis the average size of the islands was found to be ~ 25 nm. The SAD pattern in a [001] zone axis further confirmed the epitaxial nature and ordering of the FePt nanostructures. Multilayered FePt nanoislands were synthesized with three layers of FePt islands stacked one on top of another with TiN template in between. Preliminary magnetic measurements showed that such samples are predominantly perpendicularly magnetized and have high values of coercivity, Hc=1650 Oe at 300 K and Hc=4000 Oe at 5 K. Analysis of the FC (field cooled) and ZFC (zero field cooled) curves showed a blocking temperature of ~ 250 K and a curie temperature beyond 300 K.
9:00 PM - P10.5
Fabrication of Fe-Pt Alloy Particles by Pulsed Laser Ablation in Organic Solution.
Yoshie Ishikawa 1 , Kenji Kawaguchi 1 , Takeshi Sasaki 1 , Naoto Koshizaki 1
1 Nanoarchitectonics Research Center, Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
Show Abstract9:00 PM - P10.6
Molecularly Braided Chains of FePt Nanoparticles: Directed Templateless Synthesis, Assembly, Stability and Magnetic Properties.
Qingyu Yan 1 , Darshan Gandhi 1 , Arup Purukayastha 1 , Huafang Li 1 , Ganapathiraman Ramanath 1
1 Matierials Science, Rensselaer Polytechnic Institute, Troy, New York, United States
Show Abstract9:00 PM - P10.8
Hydrothermal Synthesis of Zinc-Doped Magnetite Nanoparticles.
Monica Sorescu 1 , Lucian Diamandescu 2 , Doina Tarabasanu-Mihaila 2 , Valentin Teodorescu 2
1 Physics, Duquesne University, Pittsburgh, Pennsylvania, United States, 2 Materials Science, National Institute for Materials Physics, Bucharest Romania
Show AbstractHydrothermal techniques have been used to synthesize samples of ZnxFe3-xO4 (x=0.0-1.0) starting with ZnSO4.7H2O/FeSO4.7H2O aqueous solution. The sequence of phases, structural and magnetic properties were followed by X-ray diffraction (XRD), Mössbauer spectroscopy and transmission electron microscopy (TEM). Refinement of the XRD spectra yielded the dependence of the lattice parameters of zinc–doped magnetite and zinc ferrite phase as function of the Zn molar concentration x. As well, the particle diameter was derived and represented as a function of Zn content x. As a function of Zn concentration, the phase content of hydrothermally synthesized samples was found to consist of zinc-doped magnetite, goethite and zinc ferrite. Consistent with the XRD results, Mössbauer spectroscopy data indicate the presence of magnetite and goethite at x≤0.2, magnetite and zinc ferrite at x≤0.9 and pure zinc ferrite only at high zinc concentrations. The presence of different magnetite phases was confirmed by TEM and particles with a size of 50 nm were identified. Our results show that zinc ferrite is formed at high zinc concentration by the hydrothermal method and an acicular component of goethite-magnetite is obtained at low zinc content.