Eckhard Quandt University of Kiel
Manfred Wuttig University of Maryland
Dwight Viehland Virginia Institute of Technology
Ce-Wen Nan Tsinghua University
Q1: Magnetoelectric Laminates I
Monday AM, November 28, 2011
Room 303 (Hynes)
9:30 AM - **Q1.1
Magnetoelectric Coupling in Resonant Frequency-Tunable Multiferroic Composite Bimorph Structures.
Peter Finkel 1 , Sam Lofland 2 , Dwight Viehland 3 , Jiefang Li 3 Show Abstract
1 , NUWC, Newport, Rhode Island, United States, 2 , Rowan University , Glassboro, New Jersey, United States, 3 , Virginia Tech, Blacksburg, Virginia, United States
We report on a giant tunable enhanced resonant magnetoelectric (ME) coupling in multiferroic magnetostrictive/piezoelectric composite bimorph structures. Implementing tunable pre-stress in a fix-fix double clamped ME bimorph it is possible to achieve high effective enhancement of the ME coupling coefficient (almost up to two orders of magnitude in selected cases) in a controllable resonant mode in a wide frequency range. The approach uses a magnetic/electric field assisted stress-reconfigurable resonance yeilds frequency tuning of up to 100%. The studies were performed by laser Doppler spectroscopy. We also show that this principle of a continuously tuned resonance might be used to improve sensitivity for ME magnetic sensors.
10:00 AM - **Q1.2
Expected Equivalent Magnetic Noise Spectral Density of ME as Magnetic Sensors: From Theory to Experiments.
Xin Zhuang 1 , Marc Lam Chok Sing 1 , Christophe Cordier 1 , Sébastien Saez 1 , Christophe Dolabdjian 1 , JieFang Li 2 , Keith McLaughlin 3 , Dwight Viehland 2 Show Abstract
1 , GREYC UCBN ENSICAEN CNRS, Caen France, 2 Departement of Materials science and Engineering, Virginia Tech, Blacksburg, Virginia, United States, 3 , SAIC, Inc., McLean, Virginia, United States
MagnetoElectric (ME) composites have high potential as very sensitive magnetic field sensors. Until now, numerous groups have worked on the development of high sensitivity ME sensors in order to compete with classical magnetometers based on Fluxgate, Searchcoil, GMR, GMI, SQUID... For ME sensors, the sensed magnetic signal is converted into an electrical or voltage signal via elastic strain or stress interactions, between magnetostrictive and piezoelectric layers. Thus, a strong current or voltage coupling effect is realized via magnetostrictive-piezoelectric properties. These two elastic elements have been regarded as mechanical voltage and current sources, respectively. Finally, the ME laminated composite sensors have to be considered as a field to voltage or charge converter. After optimally matching the latter to a voltage or current pre-amplifier, the equivalent magnetic noise spectral density in T/sqrt(Hz) is the best way to determine the intrinsic magnetic sensor sensitivity to a small magnetic field variation: the lower the noise level, the better the sensor resolution… Here, we will present the state of art of ME sensor noise level measurements. Furthermore, the equivalent magnetic spectral noise density level for magnetostrictive-piezoelectric laminated composites will be described and exemplified for a Longitudinal-Transverse (LT) mode. Our theoretical description, including the Mason’s model, is compared well to our experimental results. Presently, the findings show that the dielectric loss factor and mechanical force of the piezoelectric layer are the dominant sources of the noise floor in the 0.01 to 100 kHz frequency range. The equivalent magnetic noise spectral density scales as one over square root of the frequency with a white noise level (with a possible optimal noise level at the resonant frequency). Our model well explains the ME sensor behavior and helps to predict the sensor noise spectral density. From our best developments, we achieve a noise spectral density of 5 pT/ sqrt(Hz), 50 fT/sqrt(Hz) and 20 fT/sqrt(Hz) at 1 Hz, in white noise and at the resonant frequency, respectively. Also, we analyze our model versus the material properties, sensor design and electronic conditioning in order to give an idea of the expected ultimate realistic performances in the given set-up.
10:30 AM - Q1.3
Equivalent Magnetic Noise in Magnetoelectric Metglas/Piezofiber Composite.
Yaojin Wang 1 , Jiefang Li 1 , Dwight Viehland 1 Show Abstract
1 Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia, United States
The magnetoelectric (ME) effect has attracted significant interest in recent years due to potential multifunctional devices applications such as passive magnetic field sensors, non-volatile electric-write/magnetic-read memories, etc. In particular, giant ME coupling found in Metglas/piezofiber laminate composites opens the possibility of magnetic field sensor applications. The practical usefulness of a magnetic sensor is determined not only by the output signal of the sensor in response to an incident magnetic field, but also by the equivalent magnetic noise generated in the absence of an incident field. The challenge of fabricating a ME composite with a high ME coefficient αE and a low equivalent magnetic noise has restricted the realization of ME magnetic sensors. There have been limited reports on ME sensors that exhibit low frequency (f<10 Hz ) equivalent magnetic noise levels on the orders of 20 pT Hz-1/2 range, which is still between one and two orders larger than that of optically pumped ultralow magnetic field sensors. The reduction of equivalent magnetic noise is perhaps the most difficult technical obstacles to practical use of ME magnetic sensors. Hence, a theoretical analysis of noise sources, and evaluation of resultant equivalent magnetic noise of each source, is crucial for a complete understanding of ME magnetic sensors. Studies of the constituent noise sources, and the corresponding equivalent magnetic noise, have previously been deficient, in particular with regards to the relative magnitude of the equivalent noise.Here, will present the imperative theoretical modeling of various noise sources in ME sensors. In particular, the magnitude of the noise sources will be discussed, and the main noise source will be identified for various mode ME sensors. In turn, the equivalent magnetic noise was significantly reduced in Metglas/piezofiber sensors based on this theoretical modeling. An extremely low equivalent magnetic noise (5 pT√Hz @ 1 Hz) ME sensor was found, where αE was as large as 52 V/cm Oe at optimal bias field of Hdc=8Oe and the magnetic field sensitivity was as high as 10 pT at 1 Hz.References: John Clarke, R. H. Koch, The Impact of High-Temperature Superconductivity on SQUID Magnetometers, Science, 1988, 242, 217.Y.J. Wang, D. Gray, D. Berry, J.Q. Gao, J.F. Li, D. Viehland and H.S. Luo, Equivalent magnetic noise in magnetoelectric Metglas/Pb(Mg1/3Nb2/3)O3-PbTiO3 laminate composites, physica status solidi (RRL) - Rapid Research Letters, in press.Y.J. Wang, D. Gray, D. Berry, J.Q. Gao, M.H. Li, J.F. Li and D. Viehland, An extremely low equivalent magnetic noise (~pT√Hz) magnetoelectric sensor, Advanced Materials, in press.
10:45 AM - Q1.4
Temperature Response of Magnetostrictive/Piezoelectric Polymer Magnetoelectric Laminates.
Jon Gutierrez 1 , Andoni Lasheras 1 , Jose Manuel Barandiaran 1 , Jose Luis Vilas 2 , Maria San Sebastian 2 , Luis Manuel Leon 2 Show Abstract
1 Electricidad y Electronica, Universidad del Pais Vasco UPV/EHU, Leioa, Bizkaia, Spain, 2 Quimica Fisica, Universidad del Pais Vasco UPV/EHU, Leioa, Bizkaia, Spain
Magnetostrictive/piezoelectric hybrid composites have recently attracted renewed interest as high sensitivity sensors and actuators. One of the most common used geometry consists in laminated amorphous magetostrictive metal/piezoelectric layers, and the maximum magnetoelectric effect has been found at the electromechanical resonance of the system. Here we present results concerning the fabrication of such laminate composites sensor by using Vitrovac 4040® (Fe39Ni39Mo4Si6B12) as the magnetostrictive amorphous component and two different piezoelectric polymers: poly(vinylidene fluoride) (PVDF) and 2,6(β-CN)APB/ODPA (poli 2,6) polyimide, a new high temperature piezoelectric polymer. We have measured room temperature induced magnetoelectric voltages of 79.6 and 0.35 V/cm.Oe at the magnetoelastic resonance of the laminate when using PVDF and poli 2,6 polyimide as piezoelectric components. We have also tested the magnetoelectric response of both laminated composites at temperatures up to 85 C, and we have observed that the PVDF polymer piezoelectric response quickly decays. Even if the induced magnetoelectric voltage is low, we discuss the advantage of using new piezoelectric polymers due to their good performance at high temperatures, up to 200 C, making these laminate composites suitable for high temperature applications.
Q2: Magnetoelectric Applications
Monday AM, November 28, 2011
Room 303 (Hynes)
11:30 AM - **Q2.1
Magnetoelectric Sensor Self-Noise, Power, and Volume Trade-Space.
Keith McLaughlin 1 Show Abstract
1 , SAIC, McLean, Virginia, United States
Passive magnetoelectric (ME) sensors (constructed frompiezoelectric-magnetostrictive heterostructures) occupy a unique and advantageous region of the self-noise versus power versus size/volume magnetic sensor trade-space; low-volume, low-power, low-noise. We compare ME sensors in this trade-space with a survey of available sensor technologies. The passive piezoelectric-magnetostrictive heterostructure transduces magnetic energy into electrical energy and therefore only the readout electronics consumes energy. At low frequencies (< 10 Hz) the passive ME sensor self-noise is generally limited by the transduction of the sensor and a combination of the 1/f noise of the charge amplifier, the 1/f noise of leakage resistance, and the 1/sqrt(f) noise of the intrinsic loss of the piezoelectric material. For example, we have constructed a practical charge amplifier with a 1 Hz noise level of 0.07 fC/rtHz that consumes less than 80 mW and self-noise power is roughly inversely proportional to consumed power. At high frequencies (> 100 Hz), the passive ME sensor self-noise is generally limited by the equivalent input white-noise of the charge amplifier and the sensor transduction. The low-noise versus power envelope of the trade-space is therefore determined largely by the readout electronics noise versus consumed power. If the battery volume for a fixed lifetime is included in the sensor volume budget, then the electronics noise versus power trade-off establishes the self-noise versus volume trade-space. A sensor designer will then likely optimize the size, weight, power and cost of the sensor in this trade-space for a specific application. We discuss two low-power, long-life sensing applications for which passive ME sensors are well positioned as well as packaging and integration considerations that may be unique to ME sensors.
12:00 PM - Q2.2
Electrically-Tunable Magnetic Fringe Fields from a FeGa/PMN-PT Multiferroic Heterostructure.
Trifon Fitchorov 1 , Yajie Chen 1 , Scott Gillette 1 , Anton Geiler 1 , Carmine Vittoria 1 , Vincent Harris 1 Show Abstract
1 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States
The FeGa/Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) laminate multiferroic heterostructure has shown potential in engineering applications, such as in field transducers for the tuning of ferrite phase shifters . This structure has the advantage of being low-profile and planar, which is important in applications where scalability and low-power consumption are required. The planar composite exhibits a notable converse magnetoelectric effect. An electric field applied across the single-crystal PMN-PT piezoelectric component induces a strain-mediated magnetization inside the FeGa magnetostrictive component. The magnetostrictive FeGa layer, of dimensions of 15 x 10 x 0.4 mm, was affixed to a piezoelectric PMN-PT slab with the same planar dimensions but with a thickness of 0.5 mm. The PMN-PT is poled in the direction parallel to its thickness dimension and its  crystallographic direction. The composite structure was used in a longitudinally magnetized and transversely polarized (L-T) mode. An electrically-tuned fringe magnetic field is observed external to the heterostructure. The component of the fringe field parallel to the longitudinal dimensions FeGa is shown to have a maximum tunability of 4.5 Oe / (kV cm-1) for a bias field of 150 Oe. A bias magnetic field is applied along the longitudinal direction along the -preferred texturing of the FeGa magnetostrictive material. The FeGa component is pre-stressed to improve its magnetostrictive properties. The fringe magnetic field as a function of applied electric field follows an almost identical hysteretic pattern to the one of electrically-induced strain in the d31 direction of the PMN-PT, indicative of direct coupling between the piezoelectric and magnetostrictive components. A strong relaxation of the fringe field is observed near the electric coercivity where the electrically-induced strain changes polarity. The tuning coefficient of the fringe field is measured under different bias fields and is compared with theoretical estimates. References: A. L. Geiler, S. M. Gillette, Y. Chen, J. Wang, Z. Chen, S. D. Yoon, P. He, J. Gao, C. Vittoria and V. G. Harris, “Multiferroic heterostructure fringe field tuning of meander line microstrip ferrite phase shifter,” Appl. Phys. Lett., vol. 96, 053508, 2010.
12:15 PM - Q2.3
AC Magnetic Dipole Localization by Magnetoelectric Sensor.
Ying Shen 1 , Jiefang Li 1 , Dwight Viehland 1 , Keith McLaughlin 2 Show Abstract
1 , Virginia Tech, Blacksburg, Virginia, United States, 2 , SAIC, DC, District of Columbia, United States
We have developed magneto-electric (ME) sensors (constructed by piezoelectric and magnetostrictive heterostructures) and investigated their potential to detect magnetic field changes operated at quasi-static frequencies. Laminate ME sensors packaged with charge amplifier circuitry were fabricated into 3-component vector magnetometer units. These triple axes vector ME sensors were deployed whose output data was acquired as a function of time using a datalogger and calculated using MATLAB scripts. Estimation of the dipole position parameter was implemented with the help of Iterated Grid Search (IGS) algorithm and Cramer-Rao Bound (CRB) operated to evaluate the best fit solution. Results show good convergence and localization accuracy in all three orthogonal directions to changes both in moment direction and in distance between sensors and dipole, thus enabling localization. Advancements in ME laminate composites, incorporated into detection technology, will facilitate passive, low power hybrid uncooled sensor system for magnetic anomaly detection.
Q3: Converse Magnetoelectric Effect
Monday PM, November 28, 2011
Room 303 (Hynes)
2:30 PM - **Q3.1
Electrically Driven Magnetic Reversal with No Magnetic Field.
M. Ghidini 1 2 , X. Moya 1 , L. Phillips 1 , W. Yan 1 , J. Soussi 1 , F. Maccherozzi 3 , N. Steinke 4 , R. Mansell 4 , R. Pellicelli 2 , J. Briscoe 5 , S. Dunn 6 , C. Barnes 4 , S. Dhesi 3 , Neil Mathur 1 Show Abstract
1 Materials Science, University of Cambridge, Cambridge United Kingdom, 2 Physics, University of Parma, Parma Italy, 3 , Diamond Light source Ltd, Didcot United Kingdom, 4 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom, 5 Materials, Cranfield University, Cranfield United Kingdom, 6 Centre for Materials Research, Queen Mary University of London, London United Kingdom
MFM reveals that nickel films display local magnetic reversals when voltages are applied to juxtaposed layers of barium titanate, due to changes in perpendicular stress anisotropy that are elsewhere responsible for repeatably erasable magnetic stripe domains seen using PEEM with XMCD contrast.
3:00 PM - Q3.2
Epitaxial Fe3O4 on Ferroelectric Substrates.
Ming Liu 1 , Anand Bhattacharya 1 Show Abstract
1 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
In recent years, multiferroics materials with coupled ferromagnetic and ferroelectric orders have become an active research frontier, with the goal of voltage control of magnetism through magnetoelectric coupling. In particular, remarkable electric field modulation of magnetic anisotropy was observed at room temperature in composite multiferroics, such as spin-sprayed Fe3O4 films on PZNPT (lead zinc niobate-lead titanate and on PMNPT (lead magnesium niobate – lead titanate) substrates.(1) Here, an electric field applied across the substrate induced a giant magnetic anisotropy change which resulted in a ferromagnetic resonance field shift of 1000 Oe at room temperature was demonstrated, which shows promise for applications in novel tunable microwave devices with greater energy efficiency. Magnetite Fe3O4 is a material with several outstanding properties. It is half-metallic with a high Curie temperature of 850 K and large spin polarization. It is a mixed-valence system crystallized in the cubic inverse spinel structure, and undergoes a first-order phase transition.(2) In this work, we have synthesized epitaxial structures of Fe3O4/PMNPT, where a magnetite film was grown on single crystal PMNPT substrate with ozone-assisted molecular-beam epitaxy (OMBE). Well-defined low temperature electric transport and magnetic properties were observed, showing sharp changes of magnetization and resistance near 120 K associated with a Verwey transition. The magnetic and transport phenomena at low temperature are being explored in these materials.References:1.M. Liu, O. Obi, J. Lou, Y. J. Chen, Z. H. Cai, S. Stoute, M. Espanol, M. Lew, X. Situ, K. S. Ziemer, V. G. Harris, and N. X. Sun, Adv Funct Mater 19 (11), 1826 (2009).2.E. J. W. Verwey and P. W. Haayman Physica 8 97 (1941)
3:15 PM - Q3.3
Size-Dependent Electric Field Controlled Magnetism in Ni/PZT Bilayer Thin Films: Interface-Charge and Strain Comediated Magnetoelectric Coupling.
Zheng Li 1 , Jiamian Hu 1 , Ya Gao 1 , Yang Shen 1 , Yuanhua Lin 1 , Ce-wen Nan 1 Show Abstract
1 Dept. Materials Science &Engineering, Tsinghua University, Beijing, Beijing, China
Pb(Zr0.52Ti0.48)O3 (PZT) and Ni bilayer films were grown on Pt/Si substrates via Sol-gel spin-coating and off-axis magnetron sputtering. The Ni layers with different thickness were fabricated on the PZT layers. The magneto-optical Kerr effect (MOKE) measurement on the heterostructures demonstrated that the magnetism of the Ni thin film can be reversibly manipulated by switching the electric field applied on the PZT layer. The remanent magnetization of the Ni layer against the electric field was measured by using an AC voltage generator and the AC synchronous Kerr signal receiver in the MOKE system. A butterfly-shaped magnetization-electric field (M-E) loop at room temperature has been observed in the sample with thicker Ni layer, which tracks the butterfly-shaped strain-E loop of PZT, demonstrating a strain-induced ME coupling across the Ni/PZT interface. However, the loop of the thinner Ni layer is asymmetrical, and it explicitly illustrates an interface-charge-driven ME coupling. The subsequent experiments show that a very thin (3nm) buffer layer of Au between the Ni and PZT layers could reduce the charge-mediated coupling in this bilayer system obviously. The conclusion shows the strain-mediated coupling is the main mechanism for the magnetoelectic coupling in thicker Ni layer. Interestingly, as the thickness of the Ni layer decreases, the interface-charge-mediated coupling dominates the electric field controlled magnetism in Ni/PZT bilayer thin films.
3:30 PM - Q3.4
Non-Volatile Electric Field Tuning of Magnetic Domains in Permalloy Thin Films Coupled to Ferroelastic PZT Bilayers.
Anbusathaiah Varatharajan 1 , Samuel Bowden 2 , Arun Luykx 1 , Tieren Gao 1 , Paris Alexander 1 , John Cumings 1 , Daniel Pierce 2 , John Unguris 2 , Ichiro Takeuchi 1 Show Abstract
1 Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 2 Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
We are investigating electric field controlled magnetic domain motion in permalloy films deposited on Pb(ZrxTi(1-x))O3 (PZT) bilayers. Previously, we have shown that sol-gel derived bilayered heterostructures consisting of a tetragonal PbZr0.3Ti0.7O3 film (70 nm) above a rhombohedral PbZr0.7Ti0.3O3 film (70 nm) display large ferroelastic domains in the top tetragonal PZT layer (Adv. Mat. 21, 3497, 2009). The reversible non-volatile ferroelastic domain wall motion in this layer can serve as a basis for inducing controlled strain on magnetic thin films deposited on top. Voltage pulses are applied between patterned pads of a permalloy film sputtered on top and the bottom electrode underneath the PZT bilayer. This results in different ferroelastic domain configurations in the tetragonal PZT layer. This in turn leads to changes in magnetic domains in the permalloy film. We find that a permalloy film (50 nm) in elastic contact with the ferroelastic PZT layer exhibits sharp magnetic domain patterns usually associated with out-of-plane magnetization as imaged by magnetic force microscopy. SEMPA (scanning electron microscopy with polarization analysis) imaging reveals that the magnetic domains are indeed in-plane magnetized as expected for permalloy films. OOMMF analysis of the SEMPA data indicates presence of unusual metastable in-plane anisotropy modulation in the permalloy film. This work is supported by NSF MRSEC.
3:45 PM - Q3.5
Giant Electric Field Controlled Magnetic Anisotropy in Epitaxial BiFeO3-CoFe2O4 Thin Film Heterostructures on Single Crystal Pb(Mg0.33Nb0.77)0.7Ti0.3O3 Substrates.
Zhiguang Wang 1 , Yaodong Yang 1 , Ravindranath Viswan 1 , Jiefang Li 1 , Dwight Viehland 1 Show Abstract
1 , Virginia Tech, Blacksburgh, Virginia, United States
We have deposited epitaxial self-assembled BiFeO3-CoFe2O4(BFO-CFO) thin films on Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PMN-PT) substrates, and studied the change in magnetic anisotropy under different strain conditions induced by an applied electric field. After electric field poling of PMN-PT, we observed (i) significant decreases in the remnant magnetization (~ 80%) and coercive field (~50%) in the out-of-plane direction; (ii) a large increase of about 120% in the remnant magnetization of the in-plane direction; (iii) magnetic anisotropy energy changes of up to 3.24 erg/cm3 ; and (iv) magnetic force microscopy(MFM) line profiles that exhibited a significant change in the CFO magnetic domain response, which was proportional to the change in the remnant magnetization of the M-H loops. Together, these results demonstrate good control of the magnetic properties of the CFO nano-pillars via an electric field induced strain. Such a control allows switching of the magnetization direction under weak magnetic fields.
Q4: Magnetoelectric Composites
Monday PM, November 28, 2011
Room 303 (Hynes)
4:30 PM - **Q4.1
Enhanced Magnetoelectric Effect in New Magnetoelectric Composites.
Helen Chan 1 , Kwok Ho Lam 1 , Siu Hong Choy 1 , Ching Yin Lo 1 Show Abstract
1 Department of Applied Physics, The Hong Kong Polytechnic University, Hong Kong China
Several new magnetoelectric(ME) composites have been fabricated and characterized. These include (1) A three-phase ME composite consisting of PZT rods embedded in a matrix of Terfenol-D/epoxy pseudo 1-3 composite; (2) A magnetostrictive-piezoelectric laminated composite fabricated by sandwiching a lead-free BNKLBT ceramic plate between two Terfenol-D continuous fibre composite plates; and (3) A stress-biased ME sensor with a built-in permanent magnet, a PMN-PT single crystal and a magnetistrictive Terfenol-D rod. Details of the fabrication and measured properties of these composites will be reported.
5:00 PM - **Q4.2
Giant Converse Magnetoelectric Coupling in Layered Multiferroic Heterostructures.
Jing Lou 1 , Ming Liu 2 , Ogheneyunum Obi 1 , Nian Sun 1 Show Abstract
1 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Multiferroics are the group of materials that consist of two or more primiary ferroic properties, which are of great current interests, as they offer the possibility of magnetoelectric (ME) coupling, that is, electric field manipulation of magnetic properties (converse ME effect) or vice versa (direct ME effect),  and have led to many novel multiferroic devices, such as ultra-sensitive magnetometer, electrostatically tunable inductors,  electrostatically tunable microwave signal processing devices, [3, 4] etc. The utilization of ME materials with large converse ME coefficient into microwave signal processing devices can effectively eliminate the need of electromagnets that are heavy, slow, and power consuming. Nevertheless, the magnitude of converse ME coupling has been relative weak with an E-field induced effective magnetic field in the range of 10~50 Oe in most cases until several recent developments, even though strong direct ME coupling has been widely observed .In this presentation, we will cover several novel multiferroic heterostructures with large converse ME coefficients, including the most recent progresses exhibiting record high converse ME coefficients. In 2007, we reported the FeGaB films which exhibited a saturation magnetostriction of 70 ppm and a low FMR linewidth of 20 Oe at X-band. Multiferroic heterostructures of FeGaB/PZTN-PT showed a very strong converse ME coupling. A large coefficient of 94 Oe cm/kV and an E-field induced effective magnetic field range of 750 Oe were observed, which was also accompanied by a giant E-field tunable FMR frequency from 1.76 to 5.82 GHz. Fe3O4 exhibits a relatively low magnetostriction of 30 ppm, which however have a much lower saturation magnetization of ~5000 Gauss. Fe3O4/PZTN-PT multiferroic heterostructures fabricated by spin spray deposition showed a larger coefficient of 108 Oe cm/kV and a total E-field induced tunable effective magnetic field range of 860 Oe. Finally, by depositing Terfenol-D thin film, which has a giant magnetostriction constant of up to 1600 ppm, onto the PZN-PT single crystal to form the Terfenol-D/PZN-PT heterostructure, we demonstrated a total E-field induced tunable effective magnetic field range of 3500 Oe with an electric field of 6 kV/cm. This leads to a giant converse magnetoelectric coefficient of 580 Oe cm/kV that is several orders of magnitude higher than previous results . The possibility of achieving large converse magnetoelectric coupling in these multiferroic heterostructures makes them promising materials for effective electric field control of magnetism which has great implications.Reference:1. C. W. Nan, M. I. Bichurin, S. X. Dong, D. Viehland and G. Srinivasan, J. Appl. Phys. 103, 031101 (2008).2. J. Lou, D. Reed, M. Liu, N. X. Sun, Appl. Phys. Lett. 94, 112508 (2009).3. J. Lou, M. Liu, D. Reed, Y. Ren, and N. X. Sun, Adv. Mater., 21, 4711 (2009).4. M. Liu, O. Obi, J. Lou, et al., Adv. Funct. Mater. 19, 1826 (2009)
5:30 PM - Q4.3
Magnetoelectric Control of Magnetic Anisotropy in Ultrathin Fe Films.
Uwe Bauer 1 , Marek Przybylski 2 , Juergen Kirschner 2 , Geoffrey Beach 1 Show Abstract
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Max-Planck-Institut fuer Mikrostrukturphysik, Halle Germany
Magnetoelectric switching of the magnetization vector could enable new low-power logic devices and non-volatile memory cells. Magnetoelectric switching typically requires either complex multiferroic oxides, or mechanical coupling of the magnetic and electric order parameters via strain using magnetostrictive/piezoelectric composites. Recently it has been demonstrated that surface magnetic anisotropy in ultrathin ferromagnetic metal films can be directly controlled by application of a strong electric field . This new magnetoelectric coupling effect has been attributed to spin-dependent screening of applied electric fields at a surface or interface. Prior work has required very large applied voltages, up to 200 V, to produce significant changes to the anisotropy. In this work we apply an electric field across a high-k oxide stack of MgO and ZrO2 to induce charge at the surface of an ultrathin Fe film. It is expected that by using high-k dielectric materials more charge can be induced at the surface of the ferromagnetic film and the efficiency of the magnetoelectric effect can be enhanced. High-quality ultrathin Fe films were epitaxially grown on Ag(001) single crystal substrates, and covered with a MgO/ZrO2 stack. The MgO/Fe/Ag(001) system possesses strong perpendicular surface anisotropy, with clear out-of-plane magnetization up to the spin reorientation at 5.0 atomic layers of Fe. Under application of just a few volts across the high-k oxide stack we observe a strong magnetoelectric effect which results in significant changes to the coercivity and perpendicular anisotropy, and a shift of the spin reorientation thickness by 0.5 atomic layers. Research at MIT is supported by the National Science Foundation through grant ECCS-1128439.  T. Maruyama et al., Nature Nanotech. 4, 158 - 161 (2009)
5:45 PM - Q4.4
Converse Magnetoelectric Coupling in Multiferroic Heterostructures: Multi-Scale Modeling and Device Applications.
Jiamian Hu 1 2 , Zheng Li 1 , Guang Sheng 2 , Jingxian Zhang 2 , Long-Qing Chen 2 , Ce-Wen Nan 1 Show Abstract
1 Materials Science and Engineering, State Key Lab of New Ceramics and Fine Processing, Tsinghua University, Beijing China, 2 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
We theoretically study the converse magnetoelectric (ME) coupling, i.e., the electric-voltage control of magnetization, in layered ME heterostructures. Based on combined Landau-type analytic calculation and micromagnetic phase-field simulations, both the macroscopic magnetic properties (e.g., magnetic easy axis and coercivity) and microscopic magnetic domain structure evolution under external voltages are investigated. In particular, we present and demonstrate, using phase-field simulations, a simple and new pathway towards ultralow voltage-controlled magnetoresistive random access memory (MRAM) working on a nanoscle. This new MRAM device can simultaneously achieve ultrahigh storage capacity, ultralow power dissipation, and room-temperature high-speed operation, thus shows overall superiority over all existing MRAM technologies or proposed concepts.
Q5: Poster Session
Monday PM, November 28, 2011
Exhibition Hall C (Hynes)
9:00 PM - Q5.1
Magnetoresistivity of SPS-Sintered CoFe2O4–BaTiO3 Composites.
Marian Stingaciu 1 , Reinhard Kremer 2 , Peter Lemmens 3 , Mats Johnsson 1 Show Abstract
1 Materials and Environmental Chemistry, Stockholm University, Stockholm Sweden, 2 Solid State Research, Max Planck Institute, Stuttgart Germany, 3 Institute for Condensed Matter Physics, Technical University Braunschweig, Braunschweig Germany
Composites with different x-values in the system xCoFe2O4–(1-x)BaTiO3 were prepared by Spark Plasma Sintering (SPS). The sintering temperature was varied to influence the microstructure of the composites. The magnetoresistivity was measured up to 25 kGauss magnetic field within the temperature range 150 – 300 K. The magnetoresistance decreases almost linearly with increasing magnetic field and the values depend both on composition and temperature and increases when the temperature is lowered. The maximum value (4.1 percent) was found at 150 K for a composite with 30 vol% CoFe2O4. A magnetic hysteresis effect is present that increases with decreasing temperature. The maximum of the magnetoresistivity is in good agreement with the coercive field from the magnetic hysteresis curves. If we refer to the orientation of magnetic moments of neighbour magnetic particles it is clear that the maximal magnetoresistivity coincides with a maximum orientational disorder of magnetic moments.
9:00 PM - Q5.10
Ferroelectric Control of Orbital Magnetism and Magnetocrystalline Anisotropy in Thin-Film Fe/BaTiO3 Heterostructures.
Pavel Lukashev 1 2 , J. Burton 1 2 , Sitaram Jaswal 1 2 , Evgeny Tsymbal 1 2 Show Abstract
1 Physics and Astronomy, University of Nebraska - Lincoln, Lincoln, Nebraska, United States, 2 Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska, United States
Correlations between magnetocrystalline anisotropy energy (MAE), ferroelectric (FE) polarization, and orbital magnetic moment are studied for ferroelectric/ferromagnetic heterostructures consisting of barium titanate (BaTiO3) and thin-film iron (Fe). Using first-principles calculations we investigated six different geometries of the BaTiO3/Fe system, in particular with 1, 3, and 5 monolayers of Fe with either a free vacuum surface or Cu as a capping layer. We show that while the presence of Cu effectively removes the difference in MAE for opposite FE polarization directions in BaTiO3, in the case of a vacuum layer (instead of Cu) there is a large MAE change (~20%) upon switching of the polarization sign. This is explained by analyzing the correlation between MAE and orbital magnetic moments for different geometries and opposite polarization directions. We show that the magnetoelectric coupling between MAE and FE polarization is directly linked to the degree of the magnetoelectric coupling between orbital moment and FE polarization.
9:00 PM - Q5.11
Development of a Unique Surface Magneto-Optical Kerr Magnetometer to Study Exchange-Bias-Mediated Magnetoelectric Coupling in Composite Multiferroic Heterostructures.
Ian McDonald 1 , Steven Spurgeon 1 , Sam Lofland 2 , Mitra Taheri 1 Show Abstract
1 Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 Department of Physics and Astronomy, Rowan University, Glassboro, New Jersey, United States
With the increasing demand for more reliable and efficient memory storage systems, multiferroic materials have the potential to shift the paradigm from failure-prone magnetic storage disks with moving parts to solid state, electrically-switched magnetic memory. In this study we present a customized surface magneto-optical Kerr effect (SMOKE) magnetometer with the ability to electrically bias thin film samples in situ. The instrument is capable of performing hysteresis measurements in a longitudinal geometry with magnetic fields up to 1.2 T. The design of this instrument enables measurements of both the static and dynamic magnetic properties of multiferroic thin film materials with high surface sensitivity. We also present a study of exchange-bias-mediated magnetoelectric coupling in BiFeO3 (BFO) / LaSr0.7Mn0.3O3 (LSMO) heterostructures under electrical bias. Interfacial spin coupling between the antiferromagnetic order of the BFO and the ferromagnetic order of the LSMO is explored. The behavior and mechanisms governing magnetic domain dynamics due to ferroelectric polarization switching via electrical bias are also examined. The use of the room-temperature magnetoelectric multiferroic BFO may eventually enable the design of solid state electrically-switched magnetic memory technologies.
9:00 PM - Q5.12
Theoretical and Experimental Study on Magnetoelectric Performance in PZT-Terfenol-D/Epoxy-Amorphous Alloy Multiphase Composites.
Jing Ma 1 , Ce-wen Nan 1 , Zhan Shi 2 Show Abstract
1 Department of Materials Science and Engineering, Tsinghua University, Beijing China, 2 Department of Materials Science and Engineering, Xiamen University, Xiamen China
Based on the one-dimensional bending model of elastic mechanics, we investigated the influence of mechanical properties of each phase and the interface state on the properties of ME composite theoretically and experimentally. In a magnetic field, the asymmetric laminate ME composites produce both normal and bending strains, and the combined action of these strains determines the amplitude of ME effect in such ME composites. In the ME composites with PZT and two magnetic phases (i.e., Terfenol-D/epoxy and amorphous alloy), the magneto-elastic properties and the magnetic interaction between the two magnetic phases dominate the ME response. In the PZT-Terfenol-D/epoxy magnetoelectric (ME) composites, by introducing the amorphous alloy, which exhibits high initial permeability, piezomagnetic coefficient and strong magnetic anisotropy, the ME coefficient of the composite at low magnetic field was enhanced and the ME anisotropy performance was improved remarkably. The coexistence of Terfenol-D/epoxy and amorphous alloy in ME composites, offers the capability to exhibit high sensitivity at broader magnetic field.
9:00 PM - Q5.14
Electrostatically Tunable Inductor with Improved Operational Frequency and Quality Factor.
Jing Lou 1 , Zhijuan Su 1 , Ming Liu 2 , Massimo Pasquale 3 , Nian Su 1 Show Abstract
1 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 3 Divisione Elettromagnetismo, INRIM, Torino Italy
Inductors find widespread use in various applications, such as power electronics, communication systems, etc. Inductors with large tunability and enhanced performance would lead to new paradigm on circuit design, new electronic systems and new standards, leading to significantly enhanced tunable frequency range in RF circuits and novel adaptive power supply systems, etc. Traditional tunable inductors however, have the problems like small tunable range and high power consumption, which prevent their wide applications. Multiferroic composite materials with strong magnetoelectric (ME) coupling have led to many novel devices  such as information storage device, pico-Tesla sensitivity magnetometers,  and electrostatically tunable microwave magnetic signal processing devices  like resonators, phase shifters, filters, etc. Most recently, we have demonstrated that by using a magnetoelectric composite (Metglas/PZT/Metglas) as the inductive core, it is possible to construct an electrostatically tunable inductor.  The results show a large inductance tunable range ΔL/L of up to 450%, together with improved quality factors. However, due to the relative large thickness of the Metgals ribbons (~25um), excessive eddy current loss limits the operational frequency range in 100 kHz range, and suppresses the quality factor in single digits as well. Such drawback of the magnetoelectric tunable inductor dramatically limits its application. In this paper, we investigated the effect of Metglas thickness on the performance of the magnetoelectric tunable inductors. Different methods were used to reduce the thickness of the Metglas ribbons, including chemical etching, and mechanical rolling. With such approaches, the thickness of the Metglas can be reduced down to about 8um, which dramatically reduces the eddy current loss at higher frequencies. With zero electric field, the inductance is about 2 uH at 1 MHz, while it reduced to 1 uH with an electric field of 15 kV/cm. Compared to our previous results, the new tunable inductor show much flatter frequency response that extends its applicable range significantly into MHz range. Meanwhile, the quality factor of the tunable inductor shows great improvement. The maximum quality factor is about 7 for zero electric field, which increases to a maximum value of 14.5 with 15 kV/cm electric field. This is a much better result compared to the previous ones, which makes such tunable inductor applicable in MHz applications. Reference:1. C. W. Nan, M. I. Bichurin, S. X. Dong, D. Viehland and G. Srinivasan, J. Appl. Phys. 103, 031101 (2008).2. J. Zhai, Z. Xing, S. X. Dong, J. F. Li, and D. Viehland, Appl. Phys. Lett. 88, 062510 (2006).3. J. Lou, M. Liu, D. Reed, Y. Ren, and N. X. Sun, Adv. Mater., 21, 4711 (2009).4. J. Lou, D. Reed, M. Liu, N. X. Sun, Appl. Phys. Lett. 94, 112508 (2009).
9:00 PM - Q5.15
Analytic Modeling of 2-2 Nanocomposite Magnetoelectric Sensors for Low Frequency Applications.
Matthias Krantz 1 , Uzzal Binit Bala 1 , Martina Gerken 1 Show Abstract
1 Institute of Electrical and Information Engineering, Christian-Albrechts-Universität zu Kiel, Kiel Germany
Multilayered (2-2) nanocomposite materials consisting of alternating magnetostrictive (MS) and piezoelectric (PE) layers are promising as ultrasensitive magnetic field sensors for biomedical applications. We present an analytic model for evaluating the sensor sensitivity as a function of the number of layers in the nanocomposite, the composition of the nanocomposite as well as the substrate layer for frequencies well below the first bending mode. Using constitutive equations for the MS and PE layers and the Newtonian equations of motion for the flexural deformations of the bending vibration, our analytic model allows for calculation of the lowest order bending resonance frequency (free-free boundary conditions), the neutral plane position, and the non-resonant magnetoelectric (ME) coefficient for arbitrary ME nanocomposite multilayers with or without a substrate. We are considering the ME coefficient dE/dH for the longitudinal (H-field) - transverse (E-field) excitation obtained by normalizing the voltage ME coefficient dV/dH by the total PE layer thickness in the multilayer stack. Irrespective of possible manufacturability issues with some ME nanocomposites we have investigated the behaviour of MS-PE multilayer stacks with arbitrary even and odd numbers of layers with and without silicon substrates, whereby the total stack thickness (ME nanocomposite + substrate) was kept constant in all cases. In addition, effects of the PE to MS thickness and substrate to ME stack thickness ratios on the ME coefficient were studied systematically. The ME coefficient displays a large variation at small and even ME layer numbers and near constant behaviour at large and all odd layer numbers. For odd layer numbers we are considering nanocomposite layer sequences with MS layers at the very top and bottom. In the absence of a substrate this prevents bending and results in a small ME coefficient due to the longitudinal mode. On the other hand, for an even number of layers, e.g., a sequence of MS-PE-MS-PE we obtain bending even without a substrate. In the even layer number case at a substrate thickness of 40% of the nanocomposite thickness, the ME coefficient increases with an arctan like behaviour to large constant values with the number of layers. In the corresponding odd case the ME coefficient displays slightly greater constant values. For a substrate thickness of 1% of the nanocomposite thickness (corresponding to very thin substrates) the ME coefficient is greatest for the 2-layer system and decreases rapidly to zero with increasing layer number in the even layer number case. The intermediate case of a 20% substrate thickness displays a reversal of the low layer number behaviour and increasing ME coefficients at large layer numbers. The above phenomena can be understood when considering the neutral plane position passing through the substrate and ME stack as a result of the layer number and thickness variations.
9:00 PM - Q5.16
Room Temperature Magnetoelectric Effects on Single Slabs of Z-Type Hexaferrites.
Khabat Ebnabbasi 1 , Yajie Chen 1 , Anton Geiler 1 , Vincent Harris 1 , Carmine Vittoria 1 Show Abstract
1 , Northeastern University, Boston, Massachusetts, United States
There have been a lot of efforts in the past decade to do away with magnetic field and permanent magnets in the fabrication of microwave ferrite devices so that devices maybe tuned by an electric field and/or voltage. The advantages of tuning by electric field and/or voltage are that devices will be smaller, inexpensive, simpler and compatible with the semiconductor technology, since modern technologies trend is toward miniaturization and efficient performances. Multi-ferroic composite materials have been proposed to generate magnetic fields via voltage or the reverse where magnetic fields were induced by voltage. Multi-ferroic composites usually consisted of a magnetostrictive and a ferroelectric or piezoelectric slabs in physical contact. Magnetic field sensors have been implied and fabricated so far. Also small shifts in FMR have been observed using composites in electric field. To our knowledge tuning of ferrite microwave devices is still not practical with present composite structures.We propose an alternative approach to this problem. A single layer of magnetoelectric Z-type Sr3Co2Fe24O41 is used to induce similar changes as measured in composites. The advantage of a single layer is that it is simpler to utilize and tune devices. Microwave experimental results by us have yielded the following:1) The dielectric constant changes as much as 20% upon the application of magnetic fields as low as 2000 Oe or less . Multi-ferroic composites require much higher fields for similar changes.2) We present for the first time changes in permeability directly upon the application of an electric field less than 700 kV-m-1. Usually, changes in permeability is inferred indirectly from FMR measurements.3) We have prepared single phase Z-type hexa-ferrite particles and oriented them in a rotational magnetic field.4) We were able to affect the resistivity of our material by a simple annealing procedure in order to minimize heating effects in the sample.
9:00 PM - Q5.2
Magnetoelectric Bending Mode Structure Based on Metglas/Pb(Zr,Ti)O3 Fiber Laminates.
Junqi Gao 1 , Jiefang Li 1 , Dwight Viehland 1 Show Abstract
1 MSE, Virginia Tech, Blacksburg, Virginia, United States
We have investigated bending mode structures for bi-layer Metglas/PZT laminates. Due to the symmetric structure of the L-L mode, strains generated by the top and bottom layers of the Metglas are identical under magnetic field: thus, the L-L mode elongates or shrinks along the horizontal plane. However, the asymmetrical structure undergoes a flexural deformation under magnetic field.Near a fundamental bending frequency (FBR) of 210 Hz, the value of ME coefficients was enhanced by a factor of >20×, compared to a corresponding L-L mode of the same size. Using a charge amplifier detection method, magnetic noise floors of ≤ 0.3pT/√Hz were achieved near the FBR, which was about 100× lower than at 1 Hz and about 10× lower than that of L-L mode at the same frequency. Our findings thus demonstrate that bending mode ME sensors have the potential to significantly outperform L-L mode ones over a 50 Hz bandwidth about their fundamental bending frequency. Moreover, it is possible to design the bending mode sensor with different FBR frequencies, which can extend the practical application space for bending mode sensors.The authors would like to thank DARPA and ONR for support of this work. And thanks David Berry, Menghui Li, Ying Shen, Dr. Yaojin Wang and Dr. David Gray at Virginia Tech.
9:00 PM - Q5.3
Design of Electrode Positions in Cantilever Magnetoelectric Sensors.
Uzzal Binit Bala 1 , Matthias Krantz 1 , Martina Gerken 1 Show Abstract
1 , Institute of Electrical and Information Engineering, Christian-Albrechts-Universität zu Kiel, Kiel Germany
Magnetoelectric (ME) sensors employing a 2-2 composite of a piezoelectric layer and a magnetostrictive layer on a cantilever substrate have been demonstrated to exhibit high ME coefficients. We present simulation results on the optimal electrode positioning for the case of an insulating magnetostrictive material. For an incident ac magnetic field the magnetostrictive layer is deformed. Assuming an ideal interface lamination, the deformation is transferred to the piezoelectric material without slip. It produces a geometry-dependent bending of the cantilever beam. The deformation causes an electric potential difference across the piezoelectric material. In the case of a conductive magnetostrictive material, all surfaces of the magnetostrictive material exhibit the same electric potential clamping the surface in contact with the piezoelectric material to a specific electric potential. In contrast, an insulating magnetostrictive material acts as a series capacitance and the electric potential on the surface of the magnetostrictive material is position-dependent. Thus, an optimal electrode positioning allows for higher ME coefficients. We calculate the electric potential distribution in the cantilever beam using the finite element method (FEM). Numerical simulation results are compared to analytical results for simple layered composite cantilever structures. For a layered cantilever beam the highest ME coefficient is obtained for a small electrode close to the fixed end of the cantilever beam. A low electric potential difference is found directly at the fixed and the free end of the beam. The optimal electrode position is a function of the layer thicknesses and the material parameters. Cantilever geometries with trenches and/or weights at different positions are analyzed in numerical simulations regarding the optimal electrode positioning. For a rectangular cantilever beam with a weight at the tip operated well below the resonance frequency, we demonstrate a three-fold increase in the ME coefficient for a structured electrode compared to an electrode covering the complete surface.
9:00 PM - Q5.4
Novel Low Magnetization NiCr RF Magnetic Films for Multiferroic Heterostructures with Strong Magnetoelectric Coupling.
Ziyao Zhou 1 , Shawn Beguhn 1 , Ming Liu 1 , Shandong Li 1 2 , Scott Rand 1 , Jing Lou 1 , Xi Yang 1 , Nianxiang Sun 1 Show Abstract
1 ECE department, Northeastern University, Boston, Massachusetts, United States, 2 Physics, Fujian Normal University, Fuzhou, Fujian, China
Layered magnetic/piezoelectric multiferroic heterostructures with magnetic a thin film on piezoelectric slab provides a great opportunity to achieve strong ME coupling, such as FeGaB/PZN-PT (lead zinc niobate-lead titanate) , Fe3O4/PZN-PT , etc. High magnetostriction and low magnetization are desired in magnetic/piezoelectric heterostructures for achieving large electric-field induced effective magnetic field, which is critical for electric field tunable RF magnetic devices, such as electrostatically tunable inductors, bandpass filters, bandstop filters, resonators, phase shifters, etc[1-4]. Efforts have been made in developing high magnetostriction materials such as Galfenol (FeGa)  and FeGaB , etc. However, much less attention has been paid to achieving low saturation magnetization, which has a lot of room since many high magnetostriction alloys have high magnetization. In this work, we report new low moment NiCr magnetic alloy thin films and layered NiCr/PZT and NiCr/PZNPT multiferroic heterostructures, which were synthesized and characterized for achieving strong converse magnetoelectric coupling and large electric field tunable ferromagnetic resonance frequency at radio frequencies. Strong converse magnetoelectric coupling was observed in the NiCr/PZT and NiCr/PZNPT heterostructures, which exhibited a large electric field induced effective magnetic field shift of 415.2Oe for NiCr/PZT and 713.8Oe for NiCr/PZNPT, corresponding to a giant magnetoelectric coupling coefficient of 20.76Oe.cm/kV in NiCr/PZT heterostructures and 79.23Oe.cm/kV in NiCr/PZNPT multiferroic heterostructure. Furthermore, a high electrostatically tunable ferromagnetic resonance frequency of 1.255GHz in NiCr/PZT and 2.368GHz in NiCr/PZNPT was observed, which leads to a large tunable frequenct per unit electric field of 62.8MHz.cm/kV (NiCr/PZT) and 592MHz.cm/kV (NiCr/PZNPT)
9:00 PM - Q5.5
Surface Modified Fe-Ni Nanoparticles-Filled Polyamide 6 Composites Prepared by Ultrasound-Assisted Solution Mixing Process.
Marwa Mohamed 1 2 , Azza El-Maghraby 2 , Mona Abd El-Latif 2 , Hassan Farag 3 , Kyriaki Kalaitzidou 1 Show Abstract
1 G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Advanced Technology and New Materials Research Institute, City for Scientific Research and Technology Applications, New Borg El-Arab, Alexandria Egypt, 3 Chemical Engineering Department, Alexandria University, Alexandria Egypt
The focus of this study is to enhance the overall performance of Fe-Ni alloy/Polyamide 6 (PA6) nanocomposites which have recently been proved to be potential candidate materials for engineering applications. The main challenge in utilizing the unique properties of the nano-fillers is their homogeneous dispersion within the polymer matrix, due to the strong agglomerating tendency of the nanoparticles. In particular, Fe-Ni alloy is a supermagnetic material, so its nanoparticles have a great tendency to agglomerate. Two technical routes were employed for improving the dispersion state of Fe-Ni nanoparticles in PA6 matrix, surface modification of the nanoparticles and nanocomposite preparation by ultrasound-assisted solution mixing process. A sonication process using power ultrasonic waves facilitates breakup of nanoparticle agglomerates, which is essential for the nano-scale dispersion of filler within the polymer matrix.Nanocrystalline Fe40Ni60 nanoparticles were chemically synthesized and surface capped with self-assembled monolayer of hexadecanethiol (HDT). HDT as a ligand has a critical role in controlling the radius and dispersibility of the surface-capped metal nanoparticles. In addition, the adsorbed HDT molecules onto the surface of metal nanoparticles will form many entanglements with PA6 molecules, leading to significant improvement in the interfacial interaction between nanoparticles and polymer matrix. A novel technique was employed for the surface capping of Fe40Ni60 nanoparticles with different concentrations of HDT. The morphology and structure of the surface-capped nanoparticles were analyzed by means of Fourier transformation infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. Once the nanoparticles were synthesized and characterized, the composites were made by compounding the pristine and surface modified Fe40Ni60 nanoparticles with PA6, using the ultrasound-assisted solution mixing process (USM), and injection molding. The morphology, crystalline structure, mechanical and thermomechanical properties of the resultant composites were investigated. Results reveal that the pristine Fe40Ni60/PA6 nanocomposites prepared by USM have better mechanical and thermomechanical properties than those made by solution mixing process (SM) for all nanoparticle loadings used in the study. Thus, USM 3 wt% Fe40Ni60/PA6 shows 31% improvement in flexural strength as compared to 25% for the corresponding SM composite. Also, the loss of toughness evidenced by the decrease of impact strength upon addition of 3wt% Fe40Ni60 to PA6 is less (5%) for USM composite as compared to strength decrease (12%) for the SM one. This is mainly due to the presence of fewer and smaller particle agglomerates in the USM composites as shown by the morphological study.
9:00 PM - Q5.6
E-Field Modulation of Magnetoresistance in Multiferroic Heterostructures for Ultra-Low Power Electronics.
Ming Liu 1 , Jing Lou 1 , Yunume Obi 1 , Scott Rand 1 , Nian Sun 1 Show Abstract
1 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States
Electric field control of magnetism is of great technological importance for realizing ultra-low power data storage and tunable electronic devices (1-2). One approach of electrically manipulating magnetism can be achieved in composite multiferroics through strain mediated magnetoelectric coupling. Recently, giant electric-field induced effective magnetic field up to 860 Oe has been demonstrated in multiferroic Fe3O4/PZN-PT (lead zinc niobate – lead titanate) (2). In this work, An energy-efficiency technique for electrically modulating magnetoresistance has been demonstrated in multiferroic AMR (anisotropic magnetoresistance)NiCo/PZNPT and GMR (giant magnetoresistance)FeMn/NiFe/Cu/Co/PZN-PT heterostructures. A giant electric field (E-field) induced magnetic anisotropy caused by a strong magnetoelectric coupling is utilized to change the orientation of magnetization and thus dynamically manipulate magnetoresistance in AMR and GMR multiferroic devices. With a proper design, muti-band tunable AMR field sensor is proposed to dramatically enhance the measured field range by 15 times. In addition, two types of E-field determination of GMR in spin-valve structures are explored. The results indicate an energy efficiency approach to controlling magnetoresistance by E-field rather than magnetic field, which shows great potential for novel low power electronic and spintronic devices. 1.1.C. W. Nan, M. I. Bichurin, S. X. Dong, D. Viehland, G. Srinivasan, J Appl Phys 2008, 1032.M. Liu et al., Adv Funct Mater 19, 1826 (Jun 9, 2009).
9:00 PM - Q5.7
Exchange Biased Magnetostrictive Multilayer for Magnetoelectric Sensors.
Enno Lage 1 , Viktor Hrkac 1 , Lorenz Kienle 1 , Dirk Meyners 1 , Eckhard Quandt 1 Show Abstract
1 Institute for Materials Science, Kiel University, Kiel Germany
Magnetoelectric composites have been proven to be promising candidates for magnetic field sensor applications . In many cases as in biomedical applications not a single sensor but dense arrays of multiple sensors and even vector field sensors are needed to map magnetic field landscape of an extended volume. A precondition for the close arrangement of magnetoelectric sensors is to get rid of an external magnetic bias field which sets the optimum working point conditions. One way to achieve this, is to implement an intrinsic bias field via exchange biasing the magnetostrictive component of magnetoelectric composite sensors . Since the exchange bias effect in layered structures is mediated across the anti-ferromagnet-ferromagnet interface, the maximum thickness of a ferromagnetic layer pinned by the anti-ferromagnet is limited to a few tens of nanometers. On the other hand the magnetic volume of magnetoelectric sensors interacting with an external magnetic field should be large and in the range of 107 µm3. This work demonstrates that a multilayer stack comprising up to 40 couples of magnetostrictive ferromagnetic CoFe layer and adjacent anti-ferromagnetic MnIr layer can solve this dilemma. A prerequisite is that textural growth of the MnIr can be maintained through the topmost layers . Transmission electron microscopy analysis is carried out on cross-sectional samples and correlated to magnetic hysteresis and magnetostriction measurements of corresponding multilayer samples showing a characteristic shift with respect to the magnetic field axis.The layer thickness and angle dependence of the exchange bias field is then used to tune exchange biasing. Accordingly, the maximum piezomagnetic coefficient can be shifted to zero magnetic field. Combined with piezoelectric AlN substrate this exchange biased magnetostrictive multilayer results in magnetoelectric magnetic field sensors with optimum working point conditions at zero field.The authors gratefully acknowledge funding of this project work by the DFG in line with the collaborative research center SFB 855 ‘Magnetoelectric Composites – Future Biomagnetic Interfaces’. Jing Ma, Jiamian Hu, Zheng Li, and Ce-Wen Nan. Adv. Mater. 2011, XX, 1–26 M. Vopsaroiu, M. Stewart, T. Fry, M. Cain, and G. Srinivasan. IEEE Trans. Magn., Vol. 44, No. 11, 2008, 3017-3020 J. Nogues, and Ivan K. Schuller. J. Magn. Magn. Mat. 192 (1999), 203-232
9:00 PM - Q5.8
Laser Operated Magnetoelectric Nanocomposites.
Kazimierz Plucinski 1 , I. Kityk 2 , Nasser Alzayed 3 Show Abstract
1 Electronics, Mil. Univ. of Technology, Warsaw Poland, 2 Electrical Engineering Department, Czestochowa Univeristy of Technology, Czestochowa Poland, 3 Physics & Astronomy Dept., King Saud University, Riyadh 11451 Saudi Arabia
We have demonstrated the possibility of modelling the properties of magnetoelectric nanocomposites using an external laser beam. The studies were carried out for the (1-x)BiFeO3-xCuFe2O4(BFCu) nanocomposites with the x varying within the range 0.05 - 0.44. The samples were synthesized using the gel method.TEM observation showed that the average particles size were changed within the range 20 nm - 50 nm. As the photoinduced laser we used a 10 ns Nd:YAG laser operating at 1064 nm with pulse energy up to 100 mJ. We discovered a sharp changes in dielectric and magnetic properties under the influence of the external laser light. The power of the laser illumination was also increased. For smaller size nanocomposites the annealing temperature was higher.The magnetoelectric coefficient showed strong dependence on photoinduced laser power density and the coefficients achieved a maximum value of 420 mV/cm at magnetic field frequency of 70 kHz for nanocomposite sizes equal to about 35 nm. The effect demonstrates the reversible features. After the photoinducing laser is switched off, within several seconds the effect disappears. With decreasing temperature the observed effect is less strong. The observed effect is a consequence of a specific spin-spin interactions with the external coherent laser light. The laser light favors an excitation of the large number of photoelectron from the occupied valence band on the trapping levels including the spin-polarized. As a consequence we deal with the changes in both of the screening effects determinng the dielectric properties as well as the spin polarization responsible for the magnetic parameters. Temperature dependences indicate that a crucial role for such kinds of phenomena is also played by the phonon subsystem.
9:00 PM - Q5.9
Templating BiFeO3-CoFe2O4 Mutiferroic Nanostructures Using a Block Copolymer.
Hong Kyoon Choi 1 , Nicolas Aimon 1 , Jeong Gon Son 1 , Caroline Ross 1 Show Abstract
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Multiferroic nanostructures consisting of ferrimagnetic CoFe2O4 pillars embedded in ferroelectric BiFeO3 matrix have been extensively studied because of their versatile self-assembled structure and strong magnetoelectric coupling effect. Ramesh and co-workers showed that BiFeO3-CoFe2O4 mutiferroic nanostructure can exhibit two electrically switchable magnetic states [Nano letters 7, 1586, 2007]. However, in order to facilitate incorporation of BiFeO3-CoFe2O4 mutiferroic nanocomposites in a high density data storage or logic device, precise positioning of the CoFe2O4 pillars in the BiFeO3 matrix to form a square-symmetry array should be achieved. In this presentation, we propose a method to align BiFeO3 - CoFe2O4 and other similar self-assembled oxide nanostructures using a block copolymer as a mask to pattern a substrate. We have demonstrated that a square array can be achieved from a linear triblock terpolymer [Nano letters 9, 4364, 2009]. Here we used the same polyisoprene-b-polystyrene-b-polyferrocenylsilane (PI-b-PS-b-PFS) triblock terpolymer to pattern a SrTiO3 substrate on which the nanocomposite was grown. The PI-b-PS-b-PFS film, annealed in chloroform vapor, forms a square array of PFS and PI cylinders in a PS matrix with a period of 44 nm. An ordered square array of holes was produced by immersing the PI-b-PS-b-PFS film in hexane, a good solvent for PI and poor solvent for PS and PFS. This hole array film was used as a mask for etching the SrTiO3 surface. A square array of pits ~1-2 nm deep was produced on the surface of the SrTiO3 by etching in aqua regia, followed by removal of the residual polymer. The nucleation of CoFe2O4 in these pits was studied by growing very thin films of CoFe2O4 onto both etched and unetched substrates and correlating the positions of the CoFe2O4 nanocrystals with the pits. The BiFeO3-CoFe2O4 nanocomposite was grown by alternately depositing from CoFe2O4 and BiFeO3 targets in a pulsed laser deposition process, allowing the composition of the nucleation layer to be controlled independently from that of the rest of the film. The magnetic properties and magnetoelectric coupling of the BiFeO3-CoFe2O4 nanostructure was characterized and related to the microstructure. The CoFe2O4 pillars show a strong out-of-plane anisotropy due to magnetoelastic effects. Not only SrTiO3 single crystal substrate, we also explored SrTiO3/CeO2/YSZ/Si substrate to grow aligned BiFeO3-CoFe2O4 nanocomposite. The application of this approach to realizing electrically assisted magnetic recording or logic devices will be discussed.
Eckhard Quandt University of Kiel
Manfred Wuttig University of Maryland
Dwight Viehland Virginia Institute of Technology
Ce-Wen Nan Tsinghua University
Q6: Thin Film Magnetoelectric Sensors
Tuesday AM, November 29, 2011
Room 303 (Hynes)
9:30 AM - **Q6.1
All-Thin-Film Magnetoelectric Heterostructures on Si Cantilevers for Magnetic Field Sensing and Energy Harvesting.
Ichiro Takeuchi 1 Show Abstract
1 Materials Science and Engineering, University of Maryland, College Park, Maryland, United States
We have been exploring all-thin-film magnetoelectric (ME) devices microfabricated on Si cantilevers. The ME layers consist of a sputtered magnetostrictive Fe0.7Ga0.3 thin film and a sol-gel derived PbZr0.52Ti0.48O3 piezoelectric thin film. Microfabricated thin film cantilever devices allow fabrication of arrays as well as integration of the devices with other circuits on a Si wafer. Various sized cantilevers have been pursued: cm long devices are patterned using laser cutting, and mm to micron sized devices are fabricated on silicon oxide/nitride/oxide (ONO) stacks and released using XeF2-based Si etching. The mechanical resonant frequencies of the cantilevers range from 100’s of Hz to 10’s of kHz, and the Q of the resonance of the cantilevers is as high as ≈2000 in vacuum. The ME coefficient is typically of the order of 10s of V/cmOe at the resonant frequencies in vacuum. We have been able to demonstrate detection of magnetic field of the order of 10s of pT at low frequencies. We have also evaluated performance of the mm sized cantilevers as electromagnetic energy harvesters. We have detected the harvested peak power of 0.7 mW/cm3 at the resonant frequency (3.8 kHz) for 1 Oe AC field for load impedance of 12.5 kΩ. The converse effect devices will also be discussed. The work is carried out in collaboration with T. Onuta, P. Zhao, Y. Wang, L. Sanchez, H. Tang, M. Wuttig, and R. Polcawich and is funded by DARPA, ARO and NSF.
10:00 AM - **Q6.2
Giant Magnetoelectric Thin Film FeCoSiB/AlN Composites.
Henry Greve 1 , Stephan Marauska 2 , Robert Jahns 3 , Eric Woltermann 1 , Reinhard Knoechel 3 , Bernhard Wagner 2 1 , Eckhard Quandt 1 Show Abstract
1 Institute for Materials Science, Kiel University, Kiel Germany, 2 Microsystems Technology, Fraunhofer Institute for Silicon Technology, Itzehoe Germany, 3 Institute of Electrical Engineering, Kiel University, Kiel Germany
So far, the highest magnetoelectric (ME) coefficients were achieved for composite materials. Here, it is generally necessary to choose materials with optimal respective properties - namely the magnetoelastic susceptibility and the piezoelectric voltage coefficient - as well as optimizing the interface between the two. Compared to classic bulk composites, thin film deposition techniques like sputtering offer the possibility to achieve far better interface properties. This plays a key role for a direct stress/strain transfer from the magnetostrictive to the piezoelectric phase. In this talk we will present the preparation and characterization of thin film FeCoSiB/AlN composites that were prepared by magnetron sputtering. For the application of magnetic field sensors, first prototypes were realized by coating Si (100) substrates with the composite film. MEMS techniques were used to form the cantilever structures with an area of the functional composite of about 15 mm2. Here, the next step will be the further miniaturization of the sensors. By controlling the cantilever geometry it is possible to tune its mechanical resonance frequency, which was found to strongly influence air damping and thus the magnetoelectric response of the device. A magnetoelectric coefficient of 1800 V/cmOe was obtained for a cantilever with a resonance frequency of 330 Hz and the sensitivity of such sensors was found to be below 10 pT/ Hz-1/2. In order to fully eliminate air damping a sensor of this type was characterized in a vacuum environment (p ≈ 10-5 mbar) showing a coefficient of 2500 V/cmOe at resonance.Funding via the DFG Collaborative Research Center SFB 855 “Magnetoelectric Composites – Future Biomagnetic Interfaces” is gratefully acknowledged.
10:30 AM - Q6.3
PZT Films Grown on Metallic Magnetostrictive Substrates for Applications in Miniature Multiferroic Magnetic Field Sensors.
Bolin Hu 1 , Y. Chen 1 , A. Yang 1 , S. Gillette 1 , T. Fitchorov 1 , A. Geiler 1 , A. Daigle 1 , Z. Wang 2 , D. Viehland 2 , C. Vittoria 1 , V. Harris 1 Show Abstract
1 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States, 2 Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia, United States
During the past decade, the ever-increasing demand for low profile and high sensitivity magnetoelectric (ME) sensors has driven the exploration of multiferroic (MF) heterostructures with strong ME coupling coefficient and lower noise floor. Here, we propose to develop a MF structure consisting of lead zirconium titanate (PZT) films grown on metallic magnetostrictive substrates (such as Metglas, FeCoV and FeNi). A strong ME coupling is anticipated by the textured growth of PZT films on the magnetostrictive substrates by using the pulsed laser deposition (PLD) technique. In this work, the low temperature (300-650 °C) growth of the PZT films has been systematically studied with different magnetostrictive substrates and buffer layers (such as Au or Pt). The PZT films are characterized for their microstructure and piezoelectric properties using scanning electron microscopy (SEM), x-ray diffraction (XRD) and piezoelectric force microscopy (PFM) etc. These measurements indicate that a high degree of crystallographic texture results in a single phase PZT films on Metglas substrates with film thicknesses ranging from 100 nm to 2 μm, and piezoelectric coefficients >50 pm/V. Additionally, films deposited on FeCoV and FeNi substrates were also investigated. Particularly, it is found that the crystallographic orientation of PZT films can be effectively tailored by use of a buffer layer (e.g. Au or Pt) and deposition conditions (i.e. oxygen pressure, temperature and laser power). A comparison in piezoelectric properties and crystallographic orientation of the PZT films on different substrates is discussed. Finally, the magnetoelectric coupling coefficient, sensitivity, noise floor and signal-to-noise ratio (NSR) are measured for these MF heterostructures. These results provide a pathway to development of miniaturized ME-based magnetic field sensors with high sensitivity and low 1/f noise floor.
10:45 AM - Q6.4
Resonant Magnetoelectric (Fe90Co10)78Si12B10-AlN MEMS Sensor.
Stephan Marauska 1 , Henry Greve 2 , Robert Jahns 3 , Hans-Joachim Quenzer 1 , Reinhard Knoechel 3 , Eckhard Quandt 2 , Bernhard Wagner 1 Show Abstract
1 Microsystems Technology, Fraunhofer Institute for Silicon Technology ISIT, Itzehoe Germany, 2 Inorganic Functional Materials, Institute for Materials Science Christian-Albrechts-University, Kiel Germany, 3 High-frequency Laboratory, Institute for Materials Science Christian-Albrechts-University, Kiel Germany
Magnetoelectric (ME) composites have high potential as very sensitive ac magnetic field sensors in the picotesla regime . Of high interest is their medical application in magneto-encephalography or –cardiography to replace state of the art sensors based on bulky and expensive SQUIDs. The integration of ME composites in microelectromechanical systems (MEMS) based on 2-2-type ME bilayer is attractive for the fabrication of small and low-cost sensors which have the potential for vector field measurements. Moreover MEMS devices can be vacuum-packaged on wafer level to enhance the resonant ME coefficient by a reduced air damping. In this talk the fabrication and characterization of the first magnetoelectric (Fe90Co10)78Si12B10-AlN MEMS sensor will be presented. Using surface micromachining processes a cantilever stack composed of SiO2/Ti/Pt/AlN/Cr/FeCoSiB was fabricated on a 6” Si (100) wafer with a thermal oxide layer. A bulk etch with XeF2 gas was used to release free moveable rectangular cantilevers. First measurements on microcantilevers with a thickness of 3.7 µm and lateral dimensions of 200 x 1000 µm showed a static ME coefficient of about 0.69 V/cmOe. In resonance at a frequency of 2.4 kHz a ME coefficient of up to 74.3 V/cmOe for an excitation field parallel to the long axis of the cantilever was measured.  R. Jahns, H. Greve, E. Woltermann, E. Lage, E. Quandt, R. H. Knöchel, IEEE Trans. Instrum. Meas. in print (2011). The authors thank the DFG for their financial support in the Collaborative Research Center SFB 855 “Magnetoelectric Composites – Future Biomagnetic Interfaces”.
Q7: Modulated Sensors/Zero Bias
Tuesday AM, November 29, 2011
Room 303 (Hynes)
11:30 AM - **Q7.1
Modulated Magnetoelectric Sensors for Wideband Measurements.
Robert Jahns 1 , Henry Greve 2 , Eric Woltermann 2 , Stephan Marauska 3 , Bernhard Wagner 3 , Eckhard Quandt 2 , Reinhard Knoechel 1 Show Abstract
1 Microwave Group, Institute of Electrical Engineering, Christian-Albrechts-University, Kiel Germany, 2 Inorganic Functional Materials, Institute for Materials Science, Christian-Albrechts-University, Kiel Germany, 3 Microsystems Technology, Fraunhofer Institute for Silicon Technology (ISIT), Itzehoe Germany
Thin film magnetoelectric (ME) sensors show ME coefficients of up to 1800V/cmOe over narrow bandwidths in the order of some Hz around their mechanical resonance frequency, which is typically at several hundred Hz (1). Moreover sensitivity levels as low as 7.1 pT/√Hz have already been demonstrated (2), making the sensors - in principle - suitable for biomagnetic measurements like Magnetoencephalography (MEG) and Magnetocardiography (MCG). Their main advantage is the ability to work at room temperature in contrast to the nowadays used Superconducting Quantum Interference Devices (SQUIDs). Drawbacks of resonance enhanced ME measurements are the fixed measurement frequency and the low bandwidth. Biomagnetic measurements usually require high sensitivity across a wide frequency band of 0.1-100 Hz. However, at low frequencies far from resonance the ME coefficient decreases dramatically and the noise level increases; this leads to a significant decline in sensitivity. Furthermore lowering the mechanical resonance frequency down to several Hz is prohibited because it would lead to very large geometrical size.This work demonstrates a new measurement technique which allows wideband measurements at low frequencies by utilizing the nonlinear characteristics of the magnetostriction curve and a modulation approach. It offers the possibility to achieve resonance enhanced sensitivity values at virtually arbitrary frequencies outside and therefore also far below resonance. Measurements show that the sensitivity at 1 Hz can be enhanced by a factor of ~1000 compared to the non-resonant case using the proposed modulation technique. If additional Barkhausen noise can be reduced it is possible to reach the same sensitivity as in resonance. Moreover broadband measurements in the desired biomedical frequency range become possible while using high mechanical resonances. Another advantage is the high temporal resolution – sensors with higher resonance frequencies can reach sufficient temporal resolution despite of high quality factors.Furthermore coupling of mechanical vibrations is a problem of resonant driven ME sensors, especially at low frequencies. The presented modulation technique inhibits the coupling of low frequency mechanical noise into the system.(1)H. Greve, E. Woltermann, R. Jahns, S. Marauska, B. Wagner, R. Knöchel, M. Wuttig, E. Quandt, Appl. Phys. Lett. 97, 152503 (2010).(2)R. Jahns, H. Greve, E. Woltermann, E. Lage, E. Quandt, R. Knöchel, “Magnetoe-lectric Sensors for Biomagnetic Measurements”, IEEE Proceedings of MeMeA 2011, in print Funding via the DFG Collaborative Research Center SFB 855 “Magnetoelectric Composites – Future Biomagnetic Interfaces” is gratefully acknowledged.
12:00 PM - Q7.2
Low Frequency Sensitivity Enhancement of Novel PZT/Galfenol Tube Magnetoelectric Sensors by Use of Modulated Magnetostriction Technique.
Scott Gillette 1 , Yajie Chen 1 , Anton Geiler 1 2 , Jiheng Li 3 , Xuexu Gao 3 , Carmine Vittoria 1 , Vincent Harris 1 Show Abstract
1 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States, 2 , Metamagnetics Inc., Sharon, Massachusetts, United States, 3 State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing China
Improvements in sensitivity and signal-to-noise ratio of a magnetoelectric heterostructure have recently been demonstrated by taking advantage of the nonlinear magnetostrictive response using an AC magnetic-field modulation technique . The modulation technique has also demonstrated effective reduction of 1/f noise that typically hinders low-frequency sensitivity response of ME sensors, is particularly effective at mitigating external environmental noise factors, and requires no DC bias field. In this work, the modulation technique is applied to newly-developed PZT/Galfenol magnetoelectric tube sensors. The ME tube sensors consisted of a 0.56 mm diameter Galfenol wire, inserted and bonded to a PZT tube of matching inner diameter and a 1.1 mm outer diameter and were fabricated to various lengths including 5 cm and 7.5 cm. The Galfenol wire and a silver electrode painted on the exterior of the PZT tube served as electrodes for sensing the direct magnetoelectric effect in a d31 mode. When compared to the conventional DC-biased configuration, the modulation technique provides a sensitivity enhancement factor of 19.6x and a 0-Hz SNR enhancement of 38.5 dB, corresponding to a ~3 nT/√Hz noise floor, for a 7.5 cm ME tube sensor exposed to a 1mOe 25 Hz test H-field and a 100 mOe 23 KHz modulation H-field. Furthermore, magnetic spectral density plots reveal significant reduction in spurious environmental noise factors. Through utilizing the novel PZT/Galfenol tube sensors in conjunction with the modulation technique, this work demonstrates an enhancement to sensitivity, a reduction in noise floor, it eliminates the need for bulky DC biasing magnets, and provides a step towards miniaturization of magnetoelectric sensing elements making them more practically suitable for deployment in weight-sensitive gradiometric array magnetometers. References: Gillette, S. M.; Geiler, A. L.; Gray, D.; Viehland, D.; Vittoria, C.; Harris, V. G.;, "Improved Sensitivity and Noise in Magneto-Electric Magnetic Field Sensors by Use of Modulated AC Magnetostriction," Magnetics Letters, IEEE, vol.2, no., pp.2500104, 2011, doi: 10.1109/LMAG.2011.2151178
12:15 PM - **Q7.3
The Origin of Zero-Bias Magnetoelectric Effects in Functionally Graded Multiferroic Composites.
Gopalan Srinivasan 1 , G. Sreenivasulu 1 , S. Mandal 1 Show Abstract
1 Physics, Oakland University, Rochester, Michigan, United States
The traditional strain mediated magnetoelectric (ME) coupling in ferromagnetic-ferroelectric composites arises due to magnetostriction and piezoelectric effects associated with the ferroic phases. Such an ME effect, in general, requires a bias magnetic field H and an ac magnetic field. This report is on the observation and theory of ME interactions under zero-bias (H=0) in a bilayer of lead zirconate titanate (PZT) and a ferromagnetic layer in which the magnetization is graded. The systems studied include bonded Ni-Metglas and ferrites-Ni, and electrodeposited Ni-Fe. Low-frequency ME coefficient vs H data shows remanance that is indicative of a zero-bias ME effect and its magnitude is found to be dependent on the nature of graded ferromagnetic layers. The ME coefficient at H = 0 ranges from 0.1 to 1.6 V/cm Oe. The zero-bias ME coupling is attributed to strain mediated coupling between the transverse magnetization due to magnetization grading or in-plane remanant magnetization and the in-plane ac magnetic field. Theoretical estimates of ME coefficients are in general agreement with the data.
12:45 PM - Q7.4
Exchange Biased Magnetoelectric Sensor.
Dirk Meyners 1 , Enno Lage 1 , Eckhard Quandt 1 Show Abstract
1 Institute for Materials Science, Kiel University, Kiel Germany
Among others especially magnetic field sensor applications motivated much research on magnetoelectric composites in the recent past . The working point conditions of such sensor devices require a magnetic bias field of several Oersted magnitude which can be realized either by permanent magnets or electromagnets [2,3]. But, this limits the miniaturization of single sensors and might lead to unwanted crosstalk in sensor arrays. The presented work demonstrates successful implementation of an intrinsic bias field in magnetoelectric sensors via exchange bias to operate at optimum working point conditions without external bias fields as proposed by M. Vopsaroiu et al. . The exchange bias effect is commonly used for electrode stabilization in read heads and magnetic random access memory based on thin film technology . The challenge of this work is, to establish exchange biasing of large magnetic volume in conjunction with relatively low, but exact exchange bias values. The approach to the solution is a multilayer stack with intermediate anti-ferromagnetic layers coupled to the magnetostrictive ferromagnetic layer. The stack is grown on piezoelectric AlN by magnetron-sputter deposition with a 40 times repeating sequence of 2 nm Ta / 2 nm Cu / 5 nm MnIr / 20 nm FeCo followed by a 1 nm Ta cap to prevent oxidation of the surface. The direction of the exchange bias is pinned in a field cooling procedure with a defined angle θ with respect to the measurement direction of the sensor. Accordingly only a defined amount of the exchange bias field is projected onto the measurement axis. The concept’s feasibility is proven by measurements of the magnetoelectric coefficient showing a maximum of αME = 30 V/cmOe at zero field.Options for further increase of the magnetoelectric coefficient by the implementation of other highly magnetostrictive materials will be discussed. The authors gratefully acknowledge funding of this project work by the DFG in line with the collaborative research center ‘Magnetoelectric Composites – Future Biomagnetic Interfaces’. G. Srinivasan, Annu. Rev. Mater. Res. 40, 153-178 (2010) J. Zhai, Z. Xing, S. Dong, J. Li, and D. Viehland, Appl. Phys. Lett. 88, 062510 (2006) H. Greve, E. Woltermann, H.-J. Quenzer, B. Wagner, and E. Quandt, Appl. Phys. Lett. 96, 182501 (2010) M. Vopsaroiu, J. Blackburn and M. G. Cain, J. Phys. D: Appl. Phys. 40 (2007) 5027–5033 S. S. P. Parkin et al., J. Appl. Phys. 85 (8), 5828-5833 (1999)
Q8: CFO/BFO or BTO Composites
Tuesday PM, November 29, 2011
Room 303 (Hynes)
2:30 PM - Q8.1
Functionality Design and Misorientation Control in Self-Assemble Perovskite-Spinel Hetero-Eptaxial Nanostructures.
Ying-Hao Chu 1 2 Show Abstract
1 Physics and Materials Science & Engineering, UC Berkeley, Berkeley, California, United States, 2 Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan
In complex, correlated oxides, the coupling between lattice, charge, orbital, and spin degrees of freedom shows novel physical phenomena. Hetero-interfaces provide a powerful route to manipulate these degrees of freedom. In artificially fabricated hetero-interfaces, including layered structures and vertical nanostructures, interactions of these degrees of freedom results in a number of exciting discoveries, e.g. 2-dimensional electron gas at the oxide interface and strong magnetoelectric coupling in multiferroic nanostructure, etc. The lattice misorientation of the constituent materials of these heterostructures plays a decisive role in determining the couplings at the oxide interfaces. However, we notice that new physics observed in oxide heterostructures thus far has been only studied of the constituent materials with the same crystallographic orientations in each system, which is solely determined by the substrate. An interesting question arises: Can we control the relative lattice orientation of the constituent oxides in order to create interfaces with various crystallographic relationships in the heterostructures? This is also an important question because a structurally tunable oxide interface expands the degree of freedom in terms of lattice coupling and allows experimental studies of fundamental physics emerging therefrom. To answer this question, we chose a columnar CoFe2O4-BiFeO3 heterostructure as the model system and applied high-pressure reflection high energy electron diffraction (RHEED) during the growth to to in-situ monitor the growth of BiFeO3 (BFO)-CoFe2O4 (CFO) system. We recorded the RHEED patterns, which give us in-situ information about the surface structure of the sample throughout the PLD process. The structure and morphology of the film is expected to change significantly during the phase separation process. Such a technique gives us more insights on control of the self-assemble nano-structures. A novel approach to control the relative orientations of CFO and BFO by strain engineering of BFO thin films using substrates with different lattice parameters is demonstrated. We have succeeded in changing the orientation of CFO nanopillars while keeping that of BFO fixed. We also found that the tunability of CFO orientations leads to a shape control of these nanopillars, in which pyramid, roof and triangular platform are observed. We finally demonstrate how relevant physics varies with different relative crystal orientations by showing the dependence of magnetic anisotropy of CFO nanopillars on its shape and hence its crystal orientation relative to that of BFO matrices. Our findings demonstrate a high-degree control over oxide interface and therefore open a new pathway to engineer and design the functionality of hetero-epitaxial oxide nanostructures.
2:45 PM - Q8.2
Understanding the Magnetic Coupling in Epitaxial Perovskite-Spinel Nano-Composites.
Qing He 1 , Jan-Chi Yang 2 , Ying-Hao Chu 2 3 , Elke Arenholz 2 Show Abstract
1 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan, 3 Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States
The coupling of order parameters in multiferroic and magnetoelectric materials have great potential for applications in new technological devices. However, single-phase materials that simultaneously show high magnetization and ferroelectric polarization at ambient conditions remain elusive due to the incompatibility of their physical origin. An alternative approach uses coupled magnetostrictive and piezoelectric layers to realize the room-temperature magnetoelectric coupling. Some of the previous work has shown magnetoelectric coupling in an epitaxial nanostructure thin film comprised of ferrimagnetic spinel nano-pillars embedded in a ferroelectric/multiferroic perovskite matrix. However, the fundamental mechanism of this coupling is not extensively explored to date. Here we present a detailedstudy of the magnetic interaction at this type of perovskite/spinel interface using x-ray absorption (XA) spectroscopy and photoemission electron microscopy (PEEM) taking the advantage of the element sensitivity and spatial resolution of these techniques. By using x-ray magnetic linear as well as circular dichroism (XMLD, XMCD), we are able to determine the magnetic characteristics of the magnetic nanopillars and matrix separately, which in turn allows us to understand the interaction between the two components of the nanostructure. CoFe2O4 nanopillars embedded in dielectric SrTiO3, ferroelectric/antiferromagnetic BiFeO3 (BFO), and colossal magnetoresistant (La,Ca)MnO3 (LCMO) are designed as model systems . XMCD measurements in external magnetic fields at Co and Fe L-edges allow us to characterize the magnetic order and valence states as well as site occupancy in CFO pillars. In order to investigate the exchange coupling, we combined the XMCD study with angular dependent XMLD measurements at Fe and Mn L-edges, providing information about the antiferromagnetic order in BFO and orbital ordering in LCMO-. Similarly, XMCD studies at the Mn L-edges provide detailed insights into the magnetic order of the LCMO matrix, the Mn valence state and elucidate the impact of the CFO nanopillars on the LCMO magnetic order. In order to study these magnetic interfaces in detail, PEEM is used to analyze theantiferromagnetic domain structure of BFO and ferromagnetic domain structures surrounding each individual CFO nano-pillar. With the approach we gain important insights into the interfaction between the magnetic and the perovskite matrixes. For example, in the LCMO-CFO system, unexpected magnetic moment is induced in LCMO above its Curie temperature; in the BFO-CFO system, strong coupling between ferroelectric and antiferromagnetic orders causes a large enhancement of the coercivity in CFO nanopillars. These intriguing results provide important new information for the design of new magnetoelectric composite materials.
3:00 PM - Q8.3
Strain Effects in BiFeO3/CoFe2O4 Nano-Composites.
Nicolas Aimon 1 , Hong Kyoon Choi 1 , Dong Hun Kim 1 , Caroline Ross 1 Show Abstract
1 Materials science and engineering, MIT, Cambridge, Massachusetts, United States
Magnetoelectric composites composed of two multiferroic phases are promising candidates to achieve the high coupling between order parameters needed for applications such as transducers, memories and logic devices. The piezoelectricity of the ferroelectric phase and the magnetostriction of the ferromagnetic phase enable this coupling via the transfer of strain from one phase to the other. Immiscible CoFe2O4 (CFO) and BiFeO3 (BFO) form vertical nanocomposite thin films when grown on (001) single crystal SrTiO3 and (001) SrTiO3 buffered Si, in which rectangular ferrimagnetic CFO pillars are embedded in a piezoelectric BFO matrix. We focused on modeling, simulating and characterizing the strain state and magnetic anisotropy of the ferrimagnetic phase both as deposited and after electrical poling of the ferroelectric phase.
Thin films were grown in a pulsed laser deposition chamber at a base pressure of 2E-6 torr and oxygen pressures of 7.5-15mtorr. A KrF excimer laser delivering 400mJ shots at 248nm was pulsed at 10Hz to ablate ceramic targets of CoFe2O4 and Bi1.2FeO3 (enriched in Bi because of its high volatility) in stoichiometric concentrations. 100nm films were grown by either ablating material from a single composite target or by alternating two single component targets at the appropriate frequency to get sufficient mixing by diffusion in the top few layers of the substrate surface. At 660-760C, the conditions allowed to grow high quality hetero-epitaxial composite thin films of the perovskite BFO and the inverse spinel CFO on single crystal SrTiO3, as indicated by X-ray diffraction spectra. Characterization of the strain state of the two phases was performed by HRXRD and HRTEM imaging. Finite element analysis simulations were carried out on a simplified geometry where rectangular CFO pillars are arranged in a periodic array, to extract quantitative information on the transfer of strain from the strained piezoelectric matrix to the adjacent pillars. The stress/strain information was exported to a micromagnetic simulation package (OOMMF) to predict the magnetic properties of individual pillars. Vibrating sample magnetometer (VSM) and SQUID characterizations were performed to characterize the sample magnetization.
The composite thin films, as deposited, exhibit a strong out-of-plane anisotropy. This is in good agreement with both the shape anisotropy of the high aspect ratio structures and the magnetoelastic anisotropy induced by the out-of-plane compressive strain state of the CFO phase which has a negative magnetostriction coefficient. The effect of the polarization of the piezoelectric matrix is modeled by calculating the change in magnetoelastic anisotropy in the pillars caused by the change in their strain state. In this presentation we will relate the magnetic properties of the nanocomposite to the calculated and measured strain state in the CFO pillars and BFO matrix.
3:15 PM - Q8.4
E-Beam Lithography Directed Self-Assembly of CoFe2O4-BiFeO3 Nanocomposites.
Ryan Comes 1 , Hongxue Liu 1 , Mikhail Khokhlov 2 , Jiwei Lu 1 , Stuart Wolf 1 Show Abstract
1 Materials Science and Engineering, University of Virginia, Charlottesville, Virginia, United States, 2 , Guilford College, Greensboro, North Carolina, United States
Co-deposited CoFe2O4 (CFO) and BiFeO3 (BFO) films spontaneously phase segregate into a CFO pillar in a BFO matrix when grown on SrTiO3 (001) substrates. The distribution of CFO pillars is controlled by nucleation of CFO islands on the STO surface, while BFO grows layer-by-layer amongst the islands. Thus, there is no long range order in the pillar array, since the nucleation of the pillars is largely random. However, for magnetoelectric applications such as spintronic logic and memory, square arrays of pillars are preferable. To control the growth of composite CFO-BFO films, a templated substrate was fabricated. An initial uniform 12 nm CFO film was grown on STO using pulsed electron-beam deposition (PED). This film was then patterned using electron-beam lithography to produce 30-50 nm diameter CFO islands with heights of ~10 nm on the STO surface. Composite films were then deposited on the templated substrate via PED to produce ordered arrays of CFO pillars in a BFO matrix. The patterned CFO islands promote nucleation of the pillars both chemically and topographically during the self-assembled growth process. The procedure was repeated on conductive Nb-doped STO substrates to allow for ferroelectric characterization of the BFO matrix. Microstructural analysis of these films will be presented, along with magnetic force microscopy and piezoresponse force microscopy measurements. H. Zheng, Q. Zhan, F. Zavaliche, M. Sherburne, F. Straub, M.P. Cruz, L.-Q. Chen, U. Dahmen, R. Ramesh, Nano Letters 6 (2006) 1401-1407. S.A. Wolf, Jiwei Lu, M.R. Stan, E. Chen, D.M. Treger, Proceedings of the IEEE 98 (2010) 2155-2168. F. Zavaliche, T. Zhao, H. Zheng, F. Straub, M.P. Cruz, P.-L. Yang, D. Hao, R. Ramesh, Nano Letters 7 (2007) 1586-1590.
3:30 PM - Q8.5
Atomically-Flat Multiferroic BaTiO3-CoFe2O4 Epitaxial Bilayers Grown by Pulsed Laser Deposition.
Florencio Sanchez 1 , Ignasi Fina 1 , Romain Bachelet 1 , Nico Dix 1 , Chidanand Kanamadi 1 , Lourdes Fabrega 1 , Josep Fontcuberta 1 Show Abstract
1 , ICMAB - CSIC, Bellaterra Spain
Epitaxial horizontal heterostructures combining ferroelectric (FE) and ferromagnetic (FM) phases can be multiferroic and can permit magnetoelectric response via elastic coupling at the interfaces. These heterostructures typically include FE perovskite as BaTiO3 (BTO) and FM spinel oxides as CoFe2O4 (CFO), which are highly dissimilar in terms of lattice parameters and surface energy. The dissimilarity causes two problems that critically limit the development of the heterostructures: i) the tendency to three-dimensional growth due to surface energy anisotropy and lattice mismatch, and ii) the tendency to form a-oriented BTO films on CFO due to the tensile epitaxial stress. Here we report on BTO/CFO and CFO/BTO bilayers where these critical problems are overcome.BTO/CFO and CFO/BTO bilayers were prepared on SrTiO3(001) substrates with either La2/3Sr1/3MnO3 or SrRuO3 bottom electrodes using pulsed laser deposition monitored by in-situ reflection high-energy electron diffraction (RHEED). Kinetic growth limitation permitted suppression of the tendency to 3D growth of both CFO and BTO films and allowed preparation of atomically-flat (001)-oriented bilayers (either CFO/BTO or BTO/CFO). Remarkably, RHEED oscillations were monitored even in the growth of BTO on CFO. Furthermore, we used RHEED for in-situ monitoring of the lattice strain relaxation, which is complemented by ex-situ X-ray diffraction study. Finally, we show that BTO can present, including in the case of the BTO/CFO stacking sequence, remnant polarization values up to 25 μC/cm2. These results pave the way to fabricate complex multilayers with larger interfacial area and that eventually could present high magnetoelectric effect.
3:45 PM - Q8.6
Preparation and Magnetoelectric Effect in Multiferroic CoFe2O4/BaTiO3 Core-Shell Composites.
Vladimir Shvartsman 1 , Morad Etier 1 , Firas Alawneh 2 , Doru Lupascu 1 Show Abstract
1 Institute for Materials Science, University of Duisburg-Essen, Essen Germany, 2 Conservation Science Department, The Hashemite University, Zarqua Jordan
The last decade has seen a growing research interest in materials exhibiting the magnetoelectric (ME) effect . The control of the magnetic (electric) properties by applying an electric (magnetic) field promises attractive possibilities to invent novel types of sensors, driving elements, and memory devices . Of particular interest for applications are composite multiferroic materials, which exhibit a large ME effect at room temperature . In these materials the ME coupling is artificially engineered between the order parameters of ferroelectric and ferromagnetic components via a mechanical strain arising at phase interfaces under an external electric or magnetic fields. The magnitude of the ME effect depends not only on corresponding mechanical, piezoelectric, and magnetostrictive properties of the constituents, but also on the type of connectivity. In particular, an enhanced ME coupling is expected in composites with a core-shell structure due to relatively large, well-defined interface areas . We report on results of the synthesis and ME characterization of CoFe2O4-BaTiO3 core-shell composite ceramics. The samples were prepared by covering CoFe2O4 nanoparticles with a BaTiO3 layer using a sol-gel route. Such a configuration with the magnetic core surrounded by the ferroelectric layer is intended to have good insulating properties, which are crucial for effective poling of the composites in order to reach the maximal ME performance. Scanning probe microscopy studies of the samples confirmed formation of the core-shell structure with a magnetic core and piezoelectric shell . The structural, dielectric, and magnetic properties are presented. The converse ME effect, M(E), was measured using a modified SQUID ac susceptometer . The ME coefficient reaches a value of α_H approx (2.2+/-0.1)10^(-11) s/m , which surpasses those reported previously for similar structures . A change of the sign of the ME coefficient was observed for increasing magnetic bias field . This effect was related to the non-monotonic field dependence of magnetostriction in polycrystalline CoFe2O4 .1. M. Fiebig, J. Phys. D 38 R123 (2005).2. W. Eerenstein, N. D. Mathur, and J. F. Scott, Nature 442, 759 (2006).3. C. A. F. Vaz, J. Hoffman, C. H. Ahn, and R. Ramesh Adv. Mater. 22, 2900 (2010).4. V. Corral-Flores, D. Bueno-Baques, D. Carrillo-Flores, and J. A. Matutes-Aquino, J. Appl. Phys. 99, 08J503 (2006).5. V. V. Shvartsman, F. Allawneh, P. Borisov, D. Kozodaev, and D. C. Lupascu, Smart Mater. Struct. (2011 accepted)6. P. Borisov, A. Hochstrat, V. V. Shvartsman, and W. Kleemann, Rev. Sci. Instr. 78, 106105 (2007).
Q9: Magnetoelectric Thin Film Composites
Tuesday PM, November 29, 2011
Room 303 (Hynes)
4:30 PM - Q9.1
High Aspect Ratio Free Standing ZnO-Magnetostrictive Mesoscale Cylindrical Magnetoelectric Core Shell Composites.
Soeren Kaps 1 , Yogendra Mishra 1 , Rainer Adelung 1 Show Abstract
1 , Kiel University, Kiel Germany
Optimizing magnetic field sensors made by piezoelectric-magnetostrictive composites is a trade off between many parameters. Whereas large structures will cause in principle high electrical currents the mechanical coupling and the large dimensions will lead to shear losses and therefore limit the sensitivity of the sensor and make it impossible to measure small magnetic fields. In very small structures the shear losses will be negligible but the imperfections in the interfaces become more important and the typically small currents will be disturbed by, e.g., surface conductivity of the piezoelectric material and are thus difficult to measure. The best compromise is a mesoscale sensor which has relatively small losses due to shearing but still high enough electrical currents to work as a good sensor. We will introduce a design which allows the use free standing ZnO micro rods and tubes with high aspect ration as piezoelectric core material which is surrounded by a magnetostrictive layer. Since no clamping of the core shell composite is necessary in the setup, the expansion and contraction of the material is not hindered by a matrix material. The tuning of the magnetostrictive coating layer thickness can be easily optimized by changing the thickness of the magnetostrictive layer so that an optimum can be achieved for different ZnO micro rods. Furthermore, the geometry of the setup allows a multilayer deposition of exchange bias coupled giant magetostrictive materials with large polarization materials like TbFe/FeCo multilayers known to cause very high magnetostrictions. For the growth of the ZnO a newly developed process will be presented which allows the growth of a large variety of single crystals with different aspect ratios up to needles with microscale cross sections and several millimeters in length, the measured characteristic performance properties of the composite materials in the new design will be shown as well.
4:45 PM - Q9.2
Strain Profile of Complex Magnetoelectric Composite Systems by X-Ray Diffraction Methods.
Madjid Abes 1 , Christian Koops 1 , Stjepan Hrkac 1 , Olaf Magnussen 1 , Bridget Murphy 1 , Eric Woltermann 2 , Henry Greve 2 , Eckhard Quandt 2 , Soeren Kaps 3 , Rainer Adelung 3 Show Abstract
1 Institute for Experimental and Applied Physic, Christian-Albrechts-University, Kiel Germany, 2 Institute for Materials Science, Christian-Albrechts-University, Kiel Germany, 3 Institut fur Materialwissenschaft, Kiel University, Kiel Germany
Understanding the coupling at the interface between the magnetostrictive and piezoelectric components in magnetoelectric composites (ME) is essential for the optimization of theses composites for sensor applications. A large ME response is only possible if the lattice deformation induced by an external magnetic field in the magnetostrictive material can be transferred efficiently to the piezoelectric material. To study this coupling at the interface of ME composites we measured the lattice deformation in the ZnO piezoelectric component by X-ray diffraction techniques in an external magnetic field, using the high-resolution and high intensity X-ray beam provided by synchrotron sources. We employ two classes of samples for study: (Fe90Co10)78Si12B10 on cylindrical ZnO microrods (500 x 30 µm2) and on the (001) surface of high quality ZnO single crystals. From the Bragg peak positions we determined the interplanar spacings in the ZnO material and the corresponding strain. In the first class of samples, we investigated local strain distribution using small and intense X-ray beam (0.7 x 50 µm2) provided by the Nanofocus endstation of the MiNaXS-Beamline at Petra III. First results from this experiment provide information about the crystal quality and strain profiles at the interface. In the second class of samples, we determined the magnetic field induced strain profile by grazing incidence in-plane diffraction. The strain along the both  and [1-10] directions was found to increase and decrease, respectively, with the increasing of the external magnetic field oriented to the  direction, reaching a nearly constant value at fields where the magnetization of the (Fe90Co10)78Si12B10 layer reached saturation. This shows that, when the field is applied in the  direction, the ZnO substrate is under tensile and compressive strains in the  and [1-10] directions, respectively, which is in agreement with the sign of the magnetostriction of the (Fe90Co10)78Si12B10 layer.
5:00 PM - Q9.3
A Study of Strain-Mediated Interfacial Magnetoelectric Coupling in Pb(Zr0.8Ti0.2)O3/LaSr0.7Mn0.3O3 Multiferroic Heterostructures Using High Resolution Transmission Electron Microscopy and Polarized Neutron Reflectometry.
Steven Spurgeon 1 , Jennifer Sloppy 1 , Sam Lofland 2 , Christopher Winkler 1 , Lane Martin 3 , Valeria Lauter 4 , Juan Idrobo 5 , Mitra Taheri 1 Show Abstract
1 Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 Physics and Astronomy, Rowan University, Glassboro, New Jersey, United States, 3 Materials Science and Engineering, University of Illinois--Urbana Champaign, Urbana, Illinois, United States, 4 Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 5 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Multiferroic thin film heterostructures consisting of ferromagnetic and ferroelectric layers show promise for use in novel electrically-switched magnetic memory. However, the design of such devices depends on an understanding of coupling mechanisms between the two layers. Strain-mediated coupling is particularly attractive in the case of manganite materials that display highly structurally-sensitive magnetic behavior. It is known that magnetic order in magnanites arises from both double-exchange interactions that are strongly tied to the lattice. Therefore it should be possible to strain-couple a manganite film to a ferroelectric substrate and induce measurable changes in magnetic order by changing the polarization of the ferroelectric.In this study we explore role of interface structure, defects, and chemistry on magnetoelectric coupling behavior in the Pb(Zr0.8Ti0.2)O3 (PZT)/LaSr0.7Mn0.3O3 (LSMO) thin film system. The use of different underlayers allows for control of the polarization direction of the PZT layer. Subsequent changes in interface structure between two PZT polarization states and the influence on magnetic order are investigated. Using a combination of high resolution transmission electron microscopy, electron energy loss spectroscopy, bulk magnetometry, and polarized neutron reflectometry, it is possible to correlate high resolution structural, chemical, and magnetic information localized around the PZT/LSMO interface. Our results may lead to deterministic control of magnetoelectric switching and offer insight into the fundamental interaction of ferroelectric and ferromagnetic materials.
5:15 PM - Q9.4
Enhanced Ferroelectricity and Ferromagnetism in Epitaxial PbZr0.52Ti0.48O3/La0.7Sr0.3MnO3 Thin Films with a CoFe2O4 Sandwich Layer.
Devajyoti Mukherjee 1 , Robert Hyde 1 , Manh-Huong Phan 1 , Nicholas Bingham 1 , Hariharan Srikanth 1 , Pritish Mukherjee 1 , Sarath Witanachchi 1 Show Abstract
1 Department of Physics and Center for Integrated Functional Materials, University of South Florida, Tampa, Florida, United States
The recent demonstration of large magneto-electric (ME) coupling in PZT/LSMO hetero-structures based on a charge-mediated mechanism, in contrast to the strain-mediated coupling observed in other ME composites, makes it a unique system for the search of multifunctional behavior. Here, the authors present a detailed study of the growth and characterization of epitaxial PbZr0.52Ti0.48O3/La0.7Sr0.3MnO3 (PZT/LSMO) bi-layer thin films grown on single crystal MgO (100) and SrTiO3 (STO) (100) substrates using a dual-laser deposition process that combines a pulsed excimer (KrF) and a CO2 laser outputs. The optimum coupling of the laser energies produced a higher plasma plume excitation and ionization of the ablated species leading to enhanced gas phase reaction and better film morphology and crystallinity. The LSMO and PZT layers were deposited in-situ at temperatures of 750 oC and 550 oC, respectively, with LSMO acting as both the ferromagnetic layer and as top/bottom electrodes for PZT polarization. The top LSMO electrodes were deposited using a shadow mask that produced 100 μm diameter contacts. The structural characterization using x-ray diffraction (XRD) and atomic force microscopy (AFM) confirmed the single crystalline nature and the smooth surface morphology of the films. Magnetization versus magnetic field (M-H) hysteresis loops at 300 K for the PZT/LSMO (500 nm /100 nm) bi-layers showed similar behavior as LSMO single layers with an in-plane magnetic anisotropy and well saturated magnetization (Ms) values of 252 emu/cm3 and 283 emu/cm3 on MgO and STO substrates, respectively. Polarization versus electric field (P-E) hysteresis loops at 300 K for the PZT/LSMO bi-layers showed high remnant polarization (Pr) values of 77 μC/cm2 and 91 μC/cm2, on MgO and STO substrates, respectively. In order to modulate the magnetic properties of LSMO, a thin layer of CoFe2O4 (CFO) (50 nm) was sandwiched between the PZT and LSMO layers. The small lattice mismatch of CFO with LSMO, allowed for the epitaxial growth of the layers as confirmed using XRD. M-H loops at 300 K for the PZT/CFO/LSMO structures on STO and MgO substrates, respectively, exhibited higher magnetization (Ms) values of 363 emu/cm3 and 255 emu/cm3, with the easy axis along the film plane. With the introduction of hard magnetic material CFO in the PZT/LSMO bi-layer, the low coercivity of LSMO increased from ~ 0.1 kOe to ~ 2.5 kOe, irrespective of type of substrates. P-E loops for PZT/CFO/LSMO exhibited huge enhancements in polarization with Pr values of 121 μC/cm2 and 182 μC/cm2 on MgO and STO substrates, respectively. To our knowledge, such high Pr values have been observed for the first time in PZT hetero-structures. To counter-check the results, PZT/CFO/LSMO structures were grown by varying the thickness of the CFO layer. In-depth study of the micro-structure and XRD strain analysis were performed to explain the structure property relationships in PZT/CFO/LSMO structures.
5:30 PM - Q9.5
The Modulation of Transport Properties and Magnetism of Ultrathin La0.7Sr0.3MnO3 Thin Film by Thickness Effect of BaTiO3.
Zhipeng Li 1 2 , Weiguang Zhu 1 , Yong Lim Foo 2 , Zhili Dong 1 , Lan Wang 1 Show Abstract
1 , Nanyang Technological University, Singapore Singapore, 2 , Institute of Materials Research and Enginnering, A*STAR, Singapore Singapore
To study the interface effect on the electrical and magnetic properties of manganite film, ultrathin epitaxial La0.7Sr0.3MnO3 film, 2.7 nm in thickness, was deposited on SrTiO3 substrate by pulse laser deposition (PLD). The resistivity measurement shows insulating behavior from 5 K to 300 K. However, after the deposition of BaTiO3 film of 2 nm thick upon manganite, the metallicity of the manganite film is recovered with metal to insulator transition temperature of 270 K. Moreover, the saturation magnetization of the ultrathin manganite film is increased in a wide range by increasing the upper BaTiO3 thickness, while the magnetic Curie temperatures decrease. This observed interface effect breaks the limitation of manganite critical thickness and has great potential in electronic devices application. A mechanism related to strain, orbital reconstruction and ferroelectric polarization is proposed.
5:45 PM - Q9.6
To Compare the Effect of Magnetic Field Assisted Heat Treatment on Microstructure and Properties of Magnetoelectric Laminated Thin Film Composites of CoFe2O4-Pb(Zr0.52Ti0.48)O3 and NiFe2O4-Pb(Zr0.52Ti0.48)O3.
Safoura Seifikar 1 , Ali Tabei 2 , Frank Hunte 1 , Nazanin Bassiri-Gharb 2 , Justin Schwartz 1 Show Abstract
1 material Science and Engineering, North carolina State University, Raleigh, North Carolina, United States, 2 Mechanical Engineering , Georgia Institute of technology, Atlanta, Georgia, United States
Magnetoelectric (ME) thin film multilayer composites are prepared via sol-gel processing using cobalt ferrite (CFO) and nickel ferrite (NFO) as the magnetic phase and (PZT) as piezoelectric phase. During the process, samples are heat treated in magnetic fields up to 7.5 T to induce magnetic texture and improve the ME properties. To obtain the optimum annealing condition, samples are heat treated in different magnetic field and in different angles with respect to the applying field. The phase formation and orientation in both composites are evaluated by XRD and the morphology and interface are examined using electron microscopy. The effects of magnetic field annealing on the magnetic texture of the samples are also characterized using AFM and MFM techniques. The electrical polarization, magnetization and magnetoelectric properties of the composites are also measured. The main goal of this study is to compare the effect of magnetic field texturing on CFO and NFO films as hard and soft magnetic phases respectively. Our results provide compelling evidence for improving magnetic and as a consequence magnetoelectric properties of the fabricated films by in-field heat treatment. As compared with traditional annealing, the volume fraction of crystalline grains with the easy-axis aligned along the annealing magnetic field direction is enhanced as are the magnetic properties.