Disease diagnosis and treatment benefit greatly from multi-modal approaches. In addition to a range of other benefits, nanoparticles of various compositions can provide these multimodal approaches. For example, nanoparticles can provide treatment through drug delivery along with hyperthermia or photodynamic therapy. Iron oxide nanoparticles (IONPs), which can provide magnetic resonance image contrast and therapeutic heat, are emerging as a key player in this field. Combining these properties with the controlled release of drug further enhances the therapeutic efficacy of the IONP system. However, IONPs on their own are subject to disadvantages such as aggregation and dissolution in biological environments. Additionally, controlled release of drug from IONPs has been limited by low drug loading. In this work, we employ a mesoporous silica coating to confer IONPs with colloidal stability, protection against oxidation and dissolution, and a large pore volume for drug loading, making this platform a valuable tool for multi-modal therapy. In this portion of the study, this platform is used as a controlled-release system whereby IONP-generated heat acts as the controlled release mechanism.
Previous work has demonstrated that surface modification with a short polyethylene glycol chain and a hydrophobic chloro-trimethylsilane group allows high loading of a cancer therapeutic, Doxorubicin. Further, the hydrophobic form of this drug can be retained within the particle for over 24 hours without the use of any additional capping agent simply due to hydrophobic-hydrophobic interactions. Herein, we investigate system-wide temperature increases (via IONP-heating or a water bath) as a driver for increased molecular diffusion resulting in drug delivery. The effects of various drug cargoes, pore diameters, heating profiles, and release media will be presented.

Magnetic nanoparticles, (MNP), are the building-blocks for developing innovative nanodevices with multi-fold therapeutic and diagnostic activities, including magnetic fluid hyperthermia, (MFH), contrast agents for Magnetic Resonance Imaging, (CA-MRI), and targeting of tumor cells. Among the different functionalization strategies developed so far, the approaches using protein-cage structures, like those of the ferritin (Ft) family, are particularly promising, since Fts present a number of favorable properties: they have high solubility and stability in water, blood and buffers, low toxicity, and they can be easily functionalized through genetic engineering and/or chemical reactions involving one of the many chemical groups exposed to the exterior (primary amines, carboxylates, thiols).
In this contribution we present some examples of the application of a human H chain ferritin, HFt, for the realization of magnetic-based theranostic agents for the treatment of melanoma. We will show how, through the fine tuning of the composition of the ferrite nucleus grown within the proteic shell of HFt, this system can become an efficient heat mediator in the tumor treatment via MFH. Indeed, the main constraint of HFt-based MNPs is that their size cannot exceed the protein shell inner diameter (ca. 8 nm). As far as iron oxide is concerned, this size is large enough for MRI application, but it is too small for MFH, as theoretical and experimental studies demonstrated that the maximum MFH efficiency is reached for magnetite MNP of d=16-18 nm, while very poor effects are expected for d<10 nm.[1]
In particular, we will focus on highly monodisperse doped iron oxides NPs mineralized inside a genetically modified variant of HFt, carrying several copies of alfa-melanocyte-stimulating hormone peptide, which has excellent targeting properties towards melanoma cells with high selectivity,[2] and conjugated to polyethylene glycol molecules to increase their in vivo stability.
[1] L. Lartigue et al. J. Am. Chem. Soc. 133, 10459 (2011)
[2] L. Vannucci et al., Int. J. of Nanomed. 7 1489 (2012)

Radiotherapy bears the risk of long-term adverse effects as being severe cardiac complications. Strategies to improve radiotherapy therefore aim to increase the impact on the tumor or to decrease the radiation dosage in order to prevent the healthy tissue from damage. We could show that superparamagnetic iron oxide nanoparticles (SPION) may increase the therapeutic efficiency of radiotherapy by catalyzing and, thereupon, enhancing the X-ray induced production of reactive oxygen species (ROS). Two different synthesis routes were followed to prepare citrate-coated SPION that have maghemite and magnetite structures and sizes between 3 and 20 nm. Human breast cancer (MCF-7), mouse human colon cancer cells (Caco-2) and mouse fibroblasts (3T3) cells were incubated with uncoated or citrate-coated SPION and exposed to X-rays at a single dose of 3 Gy or left non-irradiated. The ablation effect of X-ray irradiation for SPION surface structures was verified using XANES spectroscopy. The ROS concentration was measured via the fluorescence intensity of the 2&’,7&’-dichlorofluorescein dye. Obviously, all internalized SPION species resulted into an enhancement of ROS formation and an additional enhancing effect due to X-ray treatment was as well manifest. Citrate-coated SPIONs in X-ray treated cells were observed to provide an enhancement in ROS formation for 240 % when compared with X-ray treated cells without internalized SPION. On the other hand, SPION internalized in non-irradiated cells caused an increase of ROS concentration up to 77 %. This implies that SPIONs do not only enhance the efficiency of X-rays on ROS formation. They also may act via their surfaces as catalyst for the Haber-Weiss cycle and moreover, contribute via releasing iron ions to the generation of ROS through the Haber-Weiss and Fenton reaction. The substantial enhancing effect due to the high-energy X-ray treatment is explained with efficient ablation of the SPION surface chemistry. The freshly formed surfaces consist now of easier accessible iron ions and thus may more effectively catalyze the ROS production than completely coated surface. The catalytic function of SPION surfaces has a promising potential for radiotherapy.

Different techniques can be used to image the biodistribution of a molecular marker in vivo, each with its own advantages and limitations. The combination of complementary modalities has attracted much attention in the past few years. For example, MRI allows in-depth whole body imaging albeit with a low sensitivity. Near infrared fluorescence imaging is more sensitive and provides resolution down to sub-cellular levels but is limited in depth due to the diffusion of light by tissues. The design of multimodal magnetic and NIR-emitting nanoparticles offers the opportunity to combine advantages from both imaging modalities.
We present here the solvothermal synthesis of multimodal probes based on Zn-Cu-In-(S,Se)/ZnS quantum dots (QDs). Their emission is tunable over the whole “optical therapeutic window” (700-900nm). The growth of manganese containing materials (Mn(x)Zn(1-x)S or MnOx) on these QDs confers them a (super)paramagnetic character. The nanoparticles are characterized by transmission electron microscopy, X-ray diffraction, electron paramagnetic resonance, inductively coupled plasma atomic emission spectroscopy and SQUID. Surface modification with polyethylene glycol allows the transfer of our nanoparticles in water. They exhibit longitudinal relaxivities on the order of 1000mM-1(QD).s-1. We finally show that these nanoparticles can be used in vivo to image lymph nodes by both MRI and NIR fluorescence imaging.

Cardiovascular disease remains the leading cause of death worldwide. As such, clinicians increasingly use magnetic resonance imaging (MRI) as a diagnostic tool to visualize the vasculature. To enhance the diagnostic capability of the imaging modality, it would be of great benefit to introduce a contrast agent that would allow for early and local diagnosis of diseased blood vessels within a patient. MRI, however, has low sensitivity to its imaging probes, thus requiring high accumulation of contrast agent in target tissue. This challenge has prompted extensive efforts to improve the contrast efficiency, or relaxivity, of superparamagnetic iron oxide nanoparticles (SPIONs), often used as negative contrast agents in MRI. A particularly successful strategy is the controlled clustering of SPIONs, which allows the overall diameter of the clustered material to be tuned within an optimal range for size-dependent relaxivity enhancement. Most clustered SPION formulations, however, still achieve a relaxivity of only 70% of their theoretical maximum. We hypothesize that a major reason for the limited enhancement is due to the properties of the cluster-inducing molecular layer. Here, we present a unique polymer that can tailor the SPION cluster to a desired size and impart a surface hydrophilicity to enhance interaction with surrounding water and bring the relaxivity within 3% of the theoretical maximum for the magnetic material. The resulting SPION cluster represented a six-fold improvement compared to commercial, unclustered SPIONs and was able to locally highlight a site of ischemia within a mouse hindlimb. We believe that the hydrophilic SPION cluster will be broadly useful in improving diagnostic quality of various acute, chronic, and malignant diseases.

Each year, considerable number of people are diagnosed with cancer and the risk is predicted to be increased in developing countries in the coming decade. Having a share of 13%, cancer is still the number one reason of death in the world. Anti - Cancer drugs that are used for treatment may have toxic effects which can cause severe complications in cancer patients. As a consequence it is necessary to design a drug delivery system to reduce the side effects and the amount of drug administered in the body.
Our work focuses on carrying and releasing the anti - cancer drug temozolomide which is widely used against a brain tumor, 4th degree astrositoma at the tumor site. Due to the drugs high hydrophobicity, the bioavailability is increased by the use of cyclodextrins, a type of oligosaccarides composed of glucose units. Cyclodextrin - Temozolomide complex is then carried via magnetic nanoparticles that are targeted to the tumor via external magnetic field.

Synthesis of magnetic iron oxide nanoparticles is performed by aqueous co-precipitation method in the presence of cyclodextrins. High pressure liquid chromotography (HPLC) and UV spectroscopy show effective capture of temozolomide in the hydrophobic core of cyclodextrins and its corresponding release. Results further show that it is possible to target the complex that is flowing inside a channel at a specified location by applying an external magnetic field in a reversible manner.
This work shows that cyclodextrin-magnetite complexes are potential candidates for the targeted delivery of toxic hydrophobic drugs using an external magnetic field.

Magnetic Particle Imaging (MPI) is a novel non-invasive biomedical imaging modality that uses safe magnetite nanoparticle contrast agents as tracers. MPI generates positive contrast images directly originated from the tracers and its predicted spatial resolution (up to sub-milimeters) and tracer mass sensitivity (~ nanograms of the tracers) make it a potential technique for cancer imaging and stem cells tracking. Whilst controlled synthesis of iron oxide nanoparticles (NPs) tracers with tuned size-dependent magnetic relaxation properties has contributed significantly to the development of MPI, additional functionalization of the same tracers for other imaging modalities such as MRI and fluorescent imaging would accelerate screening of the synthesized tracers based on their in vitro and in vivo performance in animal experiments. Here, we synthesized highly monodispersed NPs, used ligand exchange to introduce carboxyl groups on their surface and then conjugated three different types of PEG (NH2-PEG-NH2, NH2-PEG-SH and NH2-PEG-FMOC) to these NPs by amide bonding. Further, we labeled these NPs by cy5.5 near infra-red (NIRF) molecules through a click chemistry reaction. Bi-functional PEG (NH2-PEG-NH2) resulted in a larger hydrodynamic size (~100nm) of the tracers, due to linkage between some particles by amide bonding at both ends of the PEG molecules. We found that formation of these aggregates changes the MPI performance and pharmacokinetics of these multimodal contrast agents in mice animal models. Conventional T2 MRI protocols helped to quantify the biodistribution of these MPI tracers, while NIRF scanning of the excised tissues and organs enabled anatomical mapping of the tracers biodistribution and clearance pathway in reticuloendothelial organs. We believe that combination of the unique capabilities of each of these imaging modalities with the synthesis-dependent MPI performance of these NPs expedites the MPI progress toward future clinical applications.

Recently our group developed several kinds of MRI contrast agents using uniform-sized iron oxide nanoparticles. For example, using 3 nm-sized iron oxide nanoparticles, new non-toxic MRI contrast agent was realized for high resolution MRI of blood vessels down to 0.2 mm, which can be potentially applied to early diagnosis of cancers, stroke, and cardiovascular diseases.
We fabricated several kinds of magnetite nanoparticle-based nanostructured materials for magnetically separable and recyclable catalysts. A simple synthesis of noble metal (< 6 nm-sized Pd or Rh)- 20-30 nm-sized Fe3O4 heterodimer nanocrystals was achieved by controlled one-pot thermolysis of a mixture solution composed of Fe(acac)3 and Pd(acac)2 (or Rh(acac)3) in oleylamine and oleic acid. The nanocrystals catalysts exhibited good activities for various organic coupling reactions such as Suzuki coupling reaction and reduction of nitroarenes and alkenes. We reported one-pot synthesis of magnetically recyclable mesoporous silica catalyst for tandem acid-base reactions. Highly active magnetically recyclable hollow nanocomposite catalysts with a permeable carbon surface have been prepared for selective reduction of nitroarenes and Suzuki cross-coupling reactions. These catalysts could be easily separated by a magnet, and recycled consecutively.

Superparamagnetic magnetite (Fe3O4) nanoparticles have been extensively studied for hyperthermia therapy and as MRI contrast agents. By the introduction of porosity in Fe3O4 we can produce a multifunctional biomedical agent capable of hyperthermia treatment, controlled drug release triggered by magnetic heating, as well as imaging contrast enhancement. There are various synthetic methods for Fe3O4 nanoparticles, but only limited reports on the introduction and control of porosity in Fe3O4 without using sacrificial templates. Herein we used an iron complex with a mildly explosive organic ligand as the precursor and successfully obtained hollow and porous microspheres composed of Fe3O4 nanocrystals (~26 nm) using a one-step, template-free ultrasonic spray pyrolysis synthesis. The specific surface area of hollow Fe3O4 microspheres was measured to be as high as ~200 m2/g, which is comparable with the highest value reported to date. The porous structure is mostly due to the gas products produced during the decomposition of the energetic iron complex, which was also studied using TGA/DSC. Radiofrequency magnetic heating tests on the porous Fe3O4 were performed in a homemade solenoid with alternating current magnetic field (62 KHz). A heating rate of more than 1°C per minute was achieved for the aqueous suspension of porous Fe3O4, which is practical for hyperthermia therapy. Drug release and further structural/functionality optimization studies are underway to achieve slow initial drug release, stimulated drug release with radiofrequency magnetic heating, as well as higher magnetic heating rate.

Owing to their stability, non-toxicity, and high saturation magnetization, superparamagnetic iron oxide nanoparticles (SPIONs) have been an increasingly attractive contrast agent in magnetic resonance imaging (MRI) in various biomedical applications, in which SPIONs&’ surface is required to be hydrophilic and biocompatible. We report here the design and synthesis of a small and water-soluble zwitterionic dopamine sulfonate (ZDS) ligand. Following ligand exchange, the ZDS coated SPIONs (ZDS-NPs) showed small hydrodynamic diameters (~10 nm), high saturation magnetization (74 emu/g [Fe]), and stability with respect to time, pH, and salinity. ZDS-NPs also exhibited only small non-specific uptake into HeLa cancerous cells in vitro and demonstrated low non-specific binding to serum proteins in vivo in mice. Furthermore, following conjugation with streptavidin and dye the resulting ZDS-NPs nano-complexes were able to specifically target biotin receptors.
References:
1. Wei H, Insin N, Lee J, Han HS, Cordero JM, Liu W, Bawendi MG. “Compact Zwitterion-Coated Iron Oxide Nanoparticles for Biological Applications.” Nano Letters 2012, 12: 22-25.
2. Wei H, Bruns OT, Chen O, Bawendi MG. “Compact zwitterion-coated iron oxide nanoparticles for in vitro and in vivo imaging.” Integrative Biology 2013, 5: 108-114.
3. Chen O, Wei H, Maurice A, Bawendi MG, Reiss P. "Pure colors from core-shell quantum dots." MRS Bulletin 2013, 38: 696-702.

Geometric confinement is paramount to understand the magnetization processes observed in nanoscale ferromagnets, as the typical size of objects approaches characteristic magnetic length scales such as the exchange length or the domain wall width. Among the most interesting geometries for its potential application in ultrahigh density storage are continuous magnetic thin films with periodic arrays of holes, the antidots structures [1,2]. Antidot arrays allow modifying the magnetic properties of ferromagnetic films such as anisotropy, coercivity, remanence and magnetoresistance, by tuning the geometry of the arrays, in particular their size, shape and periodicity [3].
Macroscopic characterization provides indirect information on the magnetization states of antidots arrays. On the other hand, most microscopy imaging techniques provide partial information or lack the spatial resolution for a detailed characterization of closely spaced antidots arrays [4]. Particularly in Lorentz microscopy (LM), the superimposition of pure geometrical contrast limits the information that can be retrieved from the magnetic contrast. In this work, we have implemented a new approach to extract magnetic information by filtering the contrast produced by the periodic structure of the holes in LM images.
Cobalt antidots have been fabricated by focused ion beam etching of arrays of holes in 10-nm-thick cobalt films grown by sputtering on a 50-nm-thick Si3N4 membrane. Rectangular lattices of circular holes with 40 nm of diameter were produced where the distance between holes was varied from 560 to 120 nm. In arrays with a hole separation below 160 nm, Fresnel fringes mask the domain wall structures inside the arrays. Applying Fourier filtering of the diffraction contribution due to the rectangular lattices, we improve the visualization of the magnetic contrast and observe the presence of magnetic superdomains separated by horizontal and vertical stripes of magnetic contrast (superdomain walls). We have applied the Transport-of-Intensity Equation procedure to reconstruct the in-plane magnetization of the antidots arrays in Fourier-filtered LM focal series and obtain magnetization maps revealing the true orientation of magnetization inside the superdomains. In situ LM upon magnetic field has also been carried out to analyze the magnetization reversal processes of the antidot array. The magnetization switching along the easy axis occurs in two stages: nucleation and propagation of superdomains walls along the direction of the magnetic field, therefore along the perpendicular axis. These results correlate with the predictions of micromagnetic simulations.
[1] Z. L. Xiao, et. al. Nanotech, 3. 357 (2003)
[2] L. Torres, et. al. Appl. Phys. Lett., 73, 3766 (1998)
[3] C. C. Wang, et. al. Nanotechnology, 17 1629 (2006)
[4] Magnetic Microscopy of Nanostructures, ed. by H. Hopster and H. P. Oepen (Springer-Verlag Berlin Heidelberg, 2004).

Magnetic nanoparticles and nanowires present a large variety of magnetic properties. For instance, magnetic domain walls (DW) in nano-cylinders are model systems to go beyond the classical Walker limit. Fe nanocubes are very interesting for their hyperthermia applications. We developed a method combining magnetic electron holography with micromagnetism to obtain unprecedented resolution of the 3D structure at remanence of the internal DW structure in 55 nm and 85 nm diameters Ni nano-cylinders, and magnetic mapping inside of Fe nanocubes.
Ni nanowires grown by electro deposition have been recovered after dissolution of the membranes on a carbon foil for structural and magnetic TEM imaging. They present a polycrystalline structure with randomly oriented grains, leading to a random distribution of crystalline anisotropy and grain sizes roughly equal to the wire diameter. Off-axis electron holography experiments have been performed on single nano-cylinders. Before imaging, a 2 Tesla magnetic field was applied perpendicular to the nanowire axis (same direction than the electron path) using the TEM objective lens to favour the nucleation of transverse walls. Micromagnetic 3D calculations have then been computed using the OOMMF code to simulate the DW configuration for the two wire diameters. To fit the electron holography experiments, the electron beam phase shift images induced by the resulting magnetic state in the whole (X, Y, Z) space has been calculated from the micromagnetic simulations.
This method was applied to demonstrate the occurrence of a magnetic transition at remanence from a transverse wall (55 nm) to a hybrid magnetic state (85 nm) depending on the nano-cylinder diameter. Our electron holography experiments evidence the appearance of transverse walls in Ni nanocylinders which can be easily nucleated by saturating the sample perpendicular to the wire axis. As these are perfect objects to test the massless DW concept we believe they can be used to develop future spintronics devices.
Single crystal Fe nanocubes elaborated by organo-metallic chemistry have been studied by the same process using the new Hitachi TEM dedicated to Lorentz microscopy and electron holography with an unprecedent spatial resolution of 0.5 nm. Fe particles present sizes in the 15-30nm range. If monodomain states (flower state) have been observed, we will show unexpected vortex states as a function of the cube size and the applied magnetic field. The micromagnetic simulation of these magnetic states indicates changes in Fe properties compared to the bulk ones.
N. Bizière, C. Gatel, R. Lassalle-Balier, M.-C. Clochard, J.-E. Wegrowe and E. Snoeck, Nano Lett. 13, 2053-2057 (2013)
L.-M. Lacroix, S. Lachaize, F. Hue, C. Gatel, T. Blon, R. P. Tan, J. Carrey, B. Warot-Fonrose, and B. Chaudret, Nano Lett. 12, 3245-3250 (2012)
E. Snoeck, C. Gatel, L.-M. Lacroix, T. Blon, S. Lachaize, J. Carrey, M. Respaud and B. Chaudret, Nanoletters 8, 4293-4298 (2008)

A magnetic skyrmion is a nanometer-scale vortex-like spin structure with topological stability. Since discovery of skyrmions in a B20-type compound of MnSi[1], various properties have been revealed: Lorentz transmission-electron-microscopy (TEM) studies provided firm evidences of skyrmion formation and also found that thin films of B20-type compounds ubiquitously host stable skyrmions over a wide temperature - magnetic field region[2]. Near room-temperature formation of skyrmion crystal was observed in B20-type FeGe[3]. Moreover, motions of skyrmions at low current density (10^5 - 10^6 A/m^2) indicate possible electrical manipulation[4]. Such electrical controllability as well as their stable particle nature highlights potential applications for novel spintronic devices. In this talk, we will present bulk magnetic properties of B20-type germanium compounds, including Lorentz TEM observation of skyrmions[5]. Emergence of 3-dimensional skyrmion crystal state is also discussed in terms of topological Hall effects induced by Berry-phase mechanism[6]. We will further show robust formations of skyrmions in epitaxial thin films of B20-type compounds, which also produce the topological transport phenomena[7]. This work was done in collaboration with a FIRST program “Quantum Science on Strong Correlation” led by Yoshinori Tokura.
[1] S. Mühlbauer et al., Science 323, 915 (2009).
[2] X. Z. Yu et al., Nautre 465, 901 (2010).
[3] X. Z. Yu et al., Nautre Materials 10, 106 (2011).
[4] F. Joneitz et al., Science 330, 1648 (2010).
[5] K. Shibata et al., Nature Nanotech. 8, 723 (2013).
[6] N. Kanazawa et al., Phys. Rev. Lett. 106, 156603 (2011); N. Kanazawa et al., Phys. Rev. B 86, 134425 (2012).
[7] Y. Li et al, Phys. Rev. Lett. 110, 117202 (2013).

Magnetic oxide nanoparticles and hetero-systems of reduced dimensionality have attracted a lot of attention both from the stand point of basic research and for their foreseen applications. The exchange coupling in bi-magnetic core/shell nanoparticles has attracted considerable attention since the reduced dimensionality environment along with the presence of the interface may result in novel behaviors not present in bulk. In this work we analyze bi-magnetic core/shell nanoparticles based on nominal Fe3O4 and Mn3O4 oxides, by means of aberration-corrected scanning transmission electron microscopy combined with electron energy-loss spectroscopy (STEM-EELS) and theoretical calculations. As we will show, atomic scale studies are challenging because this system is very sensitive to the electron beam, and low voltages are required. Simultaneous studies of the structure, the chemistry and also the electronic properties show that the samples are very high quality, with coherent interfaces between core and shell, and that the composition is indeed Fe3O4 / Mn3O4. The Mn-oxide shell is not continuous, and is easily reduced to MnO at 200 kV, we will discuss this phase transformation and its effects on the system structure and chemistry.
Research supported by the European Research Council Starting Investigator Award STEMOX # 239739 (M.R. and J. S.),by the U.S. Department of Energy (DOE), Basic Energy Sciences (BES), Materials Sciences and Engineering Division (SJP, MV) and through a user project supported by ORNL&’s Center for Nanophase Materials Sciences (CNMS), which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.

Although lattice defects are known to severely degrade device properties, they may be utilized to locally apply functionalities in bulk materials. As one of the important lattice defects, dislocations -one-dimensional lattice defects with locally distinct atomic-scale structures - sometimes exhibit unique functional properties. For example, conductive atomic-scale wires are formed in insulating materials by segregating dopant atoms into dislocations [1]. In addition, we have succeeded in applying magnetic property to non-magnetic material dislocations [2]. In our previous study, high-density of dislocations were introduced into antiferromagnetic NiO single crystalline thin film. The dislocations show local ferromagnetic property without any dopant. The ferromagnetic dislocations show extremely large magnetic coercive force over 4 T and high Curie temperature around 520 K. By combining atomic-scale local electron energy loss spectroscopy (EELS) analysis and first principle calculations, we have revealed that the ferromagnetic property at the dislocations is according to Ni vacancies introduced along dislocation cores. For the effective usage of dislocations as functional structural elements in crystalline materials, it is desired to have a guideline to control their densities and arrays inside materials. However, there is no such guideline available at hand.
In the present study, we show the method to control the density and array of magnetic dislocations in NiO thin films by changing several factors such as lattice mismatch between single crystalline NiO thin film and substrates, post annealing temperatures and annealing atmospheres. NiO single crystalline thin film was deposited by PLD on SrTiO3 and KTaO3 single crystalline substrates. The lattice mismatch between NiO and substrates (SrTiO3 and KTaO3) is 7% and 5%, respectively. Crystallinity was improved by post annealing in air after the film deposition. The density of dislocations are successfully controlled by changing substrate. The density is 5 times higher in the film deposited on SrTiO3 substrate compared to the film on KTaO3 substrate. The relative position of dislocations are controlled by changing post annealing temperature. The dislocations are randomly distributed in the sample annealed at 1373K and they lined up along sub-grain boundary in the film annealed at 1423K. The controlled dislocations also show ferromagnetic property. Coercive force and Curie temperature of the dislocations are found to be the same with the previous results and EELS profile also show the same tendency with the previous one, so the distance or density of the dislocations is not affecting the magnetic property.
[1] A. Nakamura, et al., Nature Mater. 3 (2003) 453.
[2] I. Sugiyama, et al., Nature Nanotechnol. 8 (2013) 266.

Magnetic domain structures of the sintered Nd-Fe-B permanent magnets have been investigated in detail using Kerr microscopy, whose magnetic field has reached 2T, which is the highest magnetic field produced by the same measuring technology. The high-coercivity magnet has reached the saturated state so as to observe the magnetic domain structures easily. The reversal of domain structure in magnetization and demagnetization process of Nd-Fe-B magnets was researched. The change in microstructure caused by the distribution of Nd-rich leads to a decoupled magnetization reversal. The following phenomena was clearly observed that the magnetization reversal appears independently in each grain in a high-coercivity magnet which contains adequate Nd-rich phases along the grain boundaries, whereas the magnetization reversal appears simultaneously in a few grains in NdFeB magnet in which the Nd-rich phase along the grain boundaries is absent. It concludes that the domain passing through grain boundaries was primarily reason for making coercivity of NdFeB magnets decrease.

Magnetic properties of perovskites and related oxides are strongly affected by strain, chemical composition, and octahedral tilts. In thin films and heterostructures, distortions and local composition can vary on the scales down to atomic, making atomic-scale characterization necessary for understanding magnetic behavior. Quantitative aberration-corrected scanning transmission electron microscopy (STEM) and Electron Energy Loss Spectroscopy (EELS) can provide direct structural and chemical information at the unit cell level. First principles calculations can further be used to uncover the underlying mechanisms and develop strategies for engineering the desired behaviors.
Using this approach, we were able to investigate magnetic dead layer phenomenon in a series of LaCoO₃/SrTiO₃ thin films and heterostructures, connecting it directly to octahedral tilt behavior. We have also demonstrated that differences in magnetic behavior between La_0.5Sr_0.5CoO₃ films grown on two different substrates can be traced back to differences in the overall oxygen stoichiometry.[1] Finally, we have discovered a patchwork of different magnetic states at the interface of brownmillerite La_0.5Sr_0.5O_2.5 with NdGaO₃, while the interface with LSAT was found to be magnetically homogeneous. Prospects of atomic scale determination of magnetic order will also be discussed.
Research supported by the U.S. Department of Energy (DOE), Basic Energy Sciences (BES), Division of Materials Sciences and Engineering, and through a user project supported by ORNL&’s Center for Nanophase Materials Sciences (CNMS), which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. DOE.
References:
[1] Y.M. Kim et al., Nature Mater., 11, 888 (2012).

Among the ferrites, the cobalt ferrite CoFe2O4 has attracted much attention due to its unique and interesting structural, magnetic and optical properties which have great potential in many applications such as magnetic data storage, sensors, catalysts and drug delivery. In the present work, nanocrystalline CoFe2O4 samples have been synthesized with the help of co-precipitation method by taking pH = 7, 10 and 13 to study the effect of pH variation on structural characteristics, optical and magnetic properties of the samples. X-ray diffraction (XRD) results indicate the formation of nanocrystalline single phase mixed spinel structure with space group Fd-3m in the grown sample. Rietveld refinements of the XRD data reveal structural distortion at octahedral site due to the migration of Co2+ ions from tetrahedral to octahedral site and Fe3+ ions from octahedral to tetrahedral sites. The transmission electron microscope (TEM) and field emission scanning electron microscope (FESEM) results show that particle size decreases as value of pH increases. The UV-Vis spectra show two band gaps in all samples and the observed values of band gaps are ~ 1.43, 0.6 eV for pH=7; 1.48, 0.62 eV for pH=10 and 1.64, 0.95 eV for pH=13. The field dependence of magnetization (M-H) curves, measured at room temperature, show the ferromagnetic behavior with saturation magnetization ~ 82.36, 81.54 and 76.36 emu/gm for pH=7, 10 and 13, respectively. Thus, the value of saturation magnetization decreases with decreasing particle size. The temperature dependent magnetization (M-T) of CoFe2O4 (pH=7, 10, 13) samples measured at the applied magnetic field ~ 100 Oe show bifurcation in field cooled and zero field cooled M-T plots at TB. The value of TB decreases as the pH of samples increases, i.e as particle size decreases. The M-H plots measured at 5 K show an interesting metamagnetic transition in all samples. The correlation of the observed optical and magnetic properties with the structural characteristics of the samples will be described and discussed in this paper.

CoFe₂O₄ possesses attractive properties owing to its high coercivity, magnetocrystalline anisotropy and chemical stability[1]. When nanometer sized particles of this material are used, additionally superparamagnetic properties can be coupled to its applications. Thin films made from this material offer applications in high density storage areas as well as magnetoelectric composite manufacturing[1]. For fabrication of films, particle based solution deposition is advantageous since it provides control over the film thickness from tenth to hundreds of nanometers at shorter times with a high control over crystallinity, defined stoichiometry. In addition, possibilities for large scale up and low costs are attractive towards other vacuum-based techniques[2]. In this study, we report the structural, electrical, optical and magnetic properties of thin films manufactured via spin coating of nanoparticle dispersions of CoFe₂O₄. The nanoparticles are produced through an efficient and fast microwave assisted non-aqueous sol-gel route, yielding cobalt iron oxide particles of approx. 5 nm range[2]. For structural and morphological characterization, high resolution scanning electron microscopy, atomic force microscopy, confocal Raman microscopy and X-ray reflectometry are applied. The obtained results indicate that several hundred nanometer thick, uniform and crack free films of roughness below 1 nm are produced. Conductivity of the films is studied by making use of 4-probe electrical conductivity and discussion of determined activation energy relative to film processing. Electronic band gap of the films is determined through UV-vis measurements. Through the combination of electronic band gap probing and determination of overall electrical conduction, incl. electronic and ionic carriers, role of carriers types is discussed. Magnetic characteristics are examined via SQUID vibrating sample magnetometer to carry out room temperature B-H measurements, field cooling and zero-field cooling magnetic measurements. Conclusively, all characterization results showed that with this method CoFe₂O₄ films are manufactured with high quality and magnetic properties, which are possible to incorporate in several composite geometries with BaTiO₃ for multiferroic applications.
References
[1] Sun J, Wang Z, Wang Y, Li F. Structure and magnetic properties of CoFe2O4 nanocrystal thin films prepared by sol-gel method. 2011. p. 756-8.
[2] Kubli M, Luo L, Bilecka I, Niederberger M. Microwave-Assisted Nonaqueous SolGel Deposition of Different Spinel Ferrites and Barium Titanate Perovskite Thin Films. CHIMIA International Journal for Chemistry. 2010;64:170-2.

This study is mainly discussed the magnetic properties of nano-magnetite with morphologies of nano-particles, nano-rods, and nano-tubes. Three crystal morphologies of magnetite are prepared by using nano-hematite via carbon reduction method. The nano-particle of magnetite has a granular shape with the crystal size about 70 nm. The particle size of nano-rod is 75 nm width and 300 nm length, while nano-tube has a inner-diameter of 65 nm width and 250 nm length. It shows that all of magnetites have the ferro-magnetism by the superconducting quantum interference device magnetometer (SQUID) measurement. The coercivity of nano-particles, nano-rods, and nano-tubes is 78, 235, and 192 Oe, respectively, which has a remanence ratio (Mr/Ms) of 11/110, 17/77 and 17/81. The spatial distribution of magnetism are characterized by magnetic force microscopy (MFM). The MFM phase images exhibit bright and dark areas, implying ferro-magnetic domains in our samples. Furthermore, nano-particles, nano-rod and nano-tubes of magnetites show a complicated magnetic domain arrangement.

Inorganic nanoparticle/organic hybrid materials attract increasing attentions because of their beneficial properties of each phase. The authors reported the syntheses of ferrite nanoparticle (NP)/organic hybrids from metal-organics [1,2]. Manganese zinc ferrite is one of the soft ferrites and characterized by its high initial permeability, high resistivity, and low power loss. Manganese zinc ferrite has high frequency applications, such as magnetic recording materials, multi-layer chip inductor, and electromagnetic interference shielding. This paper describes the in situ synthesis of manganese zinc ferrite NP/cellulose hybrid nanocomposite from metal acetylacetonates below 100 centigrade. A mixture of manganese (II) acetylacetonate (MA), zinc acetylacetonate (ZA) and iron(III) 3-allylacetylacetonate (IAA) was hydrolyzed and polymerized yielding spinel oxide NP/organic hybrid. The hybrid was analyzed by FT-IR, UV-visible spectroscopy, DTA-TG, powder XRD, VSM, and SQUID. The formation of (Mn,Zn)Fe2O4 NPs in an organic matrix was confirmed by XRD analysis. The crystallite size of spinel particles was dependent upon the hydrolysis conditions of MA-ZA-IAA. Crystalline manganese zinc ferrite NPs below 5 nm were uniformly dispersed in the organic matrix. The magnetization of hybrid increased with increasing water amount for hydrolysis. The magnetization versus field curve for the manganese zinc ferrite NP/organic hybrid showed neither remanence no