Download or read book On Strain mediated Magnetoelectric Effects in Multiferroic Composite Nanostructures written by 陈海涛 and published by . This book was released on 2013 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book ON STRAIN MEDIATED MAGNETOELEC written by Haitao Chen and published by Open Dissertation Press. This book was released on 2017-01-26 with total page 150 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "On Strain-mediated Magnetoelectric Effects in Multiferroic Composite Nanostructures" by Haitao, Chen, 陈海涛, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Multiferroics which combine two or more order parameters of ferroelectricity, ferromagnetism and ferroelasticity, have drawn great interests in the past few years due to their promising potential of application in sensors, transducers, spintronics and multistate memories. Coupling between the ferroelectricity and ferromagnetism renders the induction of an electric polarization P upon applying a magnetic field, or the induction of a magnetization M upon applying an electric field which is called magnetoelectric coupling effect. There are single phase multiferroics which simultaneously possess ferroelectricity and magnetism in nature. However, these natural multiferroics only exhibit weak magnetoelectric coupling effect at very low temperature which hinders the practical applications. An alternative and more promising choice is to fabricate multiferroic composites. In the multiferroic composite systems, large magnetoelectric coupling effects can be produced indirectly from the strain-mediated interaction even at room temperature and great design flexibility can be obtained. In the present study, two types of multiferroic composite nanostructures are investigated: the vertical heteroepitaxial multiferroic thin films and film-on-substrate heterogeneous bilayers with incorporation of various influences, such as film thickness, misfit strains and flexoelectricity. Since the first fabrication of vertical epitaxial multiferroic nanostructures, great scientific interests have been attracted for the potential large magnetoelectric effects arising from the relaxed substrate constraint and large interfacial area between the ferroelectric and ferromagnetic phases. A three dimensional phase field model is devised to precisely describe the complex strain state of this nanostructure. The simulation results demonstrate that both film thickness and misfit strains are important in determining the magnitude of magnetoelectric effect. Due to the strong strain-mediated magnetoelectric coupling effect in film-on-substrate system with a ferromagnetic thin film directly growing on a thick ferroelectric substrate, precision electric control of local ferromagnetism, i.e. ferromagnetic domain pattern and domain wall properties, are achievable. The results show that the domain pattern of the ferroelectric substrate can be fully transferred onto the as-deposited ferromagnetic thin film. High stability of the magnetic domain is observed when the system is subjected to an external magnetic field. Under an applied electric field, the transferred domain pattern in magnetic film can be either maintained or erased depending on the direction of applied electric field. Moreover, when a pulse of in-plane electric field is applied, the magnetic domain wall motion can be observed in concurrence with the ferroelectric domain wall motion. With the decrease of material size, some effects that can be neglected in bulk materials may play an important role on the overall properties of material, such as flexoelectric effects which describe the induction of polarization from strain gradient. A two dimensional phase field model is adopted to study the influence of flexoelectric effects on the epitaxial ferroelectric films. A thermodynamic phenomenological model is then utilized to analyze the influence of flexoelectric effects on magnetic field induced electric polarization in the multiferroic nanocomposite b

Download or read book On Strain mediated Magnetoelectric Effects in Multiferroic Composite Nanostructures written by Haitao Chen (Ph. D.) and published by . This book was released on 2013 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Mapping Local Manifestations of the Strain Mediated Magnetoelectric Effect in Composites written by Harshkumar Trivedi and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Strain and Charge Co mediated Magnetoelectric Coupling in Thin Film Multiferroic Heterostructures written by Xinjun Wang and published by . This book was released on 2015 with total page 87 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recently, more and more researching has been focused on multiferroic materials and devices due to the demonstrated strong magnetoelectric coupling in new multiferroic materials, artificial multiferroic heterostructures and devices with unique functionalities and superior performance characteristics. This has resulted in opportunities for us to achieve compact, fast, energy efficient and voltage tunable spintronic devices. Traditionally, in magnetic materials based magnetic random access memories (MRAM) devices, magnetization is used to store the binary information. Since the high coercivity of the ferromagnetic media requires high magnetic fields for switching the magnetic states, so it needs large amount of energy. A spin torque technique that is used in Modern MRAM information writing processes minimizes the large energy for generating a magnetic field by passing through a spin-polarized current directly to the magnets. However, this two methods still consumes a lot of energy because of the large current or current density requirement to toggle the magnetic bits. Many papers reports that spin is controlled by the electrical field which supplies new opportunities for power efficient voltage control of magnetization in spintronic devices for magnetoeletric random use for memories (MERAM) with ultra-low energy consumption. However, state of the art multiferroic materials still make it chatting to realize non-volatile 180 magnetization reversal, which is desired in realizing MERAM. In a strain-mediated multiferroic system, the typical modification of the magnetism of ferromagnetic phase as a function of bipolar electric field shows a "butterfly" like behavior. This is due to the linear piezoelectricity of ferroelectric phase which has a "butterfly" like piezostrain as a function of electric field curve resulting from ferroelectric domain wall switching. Compared with charge-mediated multiferroic, the strain-mediated multiferroic system needs much higher voltage than charge-mediated, because of the thickness of ferroelectric is different. In a strain-mediated multiferroic system, the substrate is bulk materials and in a charge-mediated multiferroic system, the substrate is a thin film on dielectric material. In this work, we study the equivalence of direct and converse magnetoelectric effects. The resonant direct and converse magnetoelectric (ME) effects have been investigated experimentally. For a strain-mediated multiferroic system, we use PIN-PMN-PT, PMN-PT as the substrate. LFO, YIG, FeGaB are used as the magnetic thin film to study the tubability. This linear piezoelectric effect in converse magnetoelectric coupling would lead to "butter-fly" like magnetization vs. electric field curve which leads to a "volatile" behavior in magnetic memory system. In a charge-mediated system, we use NiFe/PLZT/Si to study the tunability. The frequency responses of direct and converse magnetoelectric effects were measured under the same electric and magnetic bias conditions. In this study, VSM and FMR are studies in different situation. Furthermore, we studied the low temperature fabricated multiferroic heterostructure, to find out the best solution to get the thin film by spin spray. Different PH and temperature are used. VSM and FMR were employed to measure properties of thin film. XRD and SEM were used to analyse the composition and surface.

Download or read book Electric Field Control of Magnetization and Electronic Transport in Ferromagnetic Ferroelectric Heterostructures written by Sen Zhang and published by Springer Science & Business Media. This book was released on 2014-04-10 with total page 143 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book mainly focuses on the investigation of the electric-field control of magnetism and spin-dependent transportation based on a Co40Fe40B20(CoFeB)/Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PMN-PT) multiferroic heterostructure. Methods of characterization and analysis of the multiferroic properties with in situ electric fields are induced to detect the direct magnetoelectric (ME) coupling. A switchable and non-volatile electric field control of magnetization in CoFeB/PMN-PT(001) structures is observed at room temperature, and the mechanism of direct coupling between the ferroelectric domain and ferromagnetic film due to the combined action of 109° ferroelastic domain switching in PMN-PT and the absence of magnetocrystalline anisotropy in CoFeB is demonstrated. Moreover, the electric-field control of giant magnetoresistance is achieved in a CoFeB-based spin valve deposited on top of (011) oriented PMN-PT, which offers an avenue for implementing electric-writing and magnetic-reading random access memory at room temperature. Readers will learn the basic properties of multiferroic materials, many useful techniques related to characterizing multiferroics and the interesting ME effect in CoFeB/PMN-PT structures, which is significant for applications.

Download or read book Strain Mediated Magnetoelectric Composites for Cell Sorting and Memory Devices written by Michael Guevara De Jesus and published by . This book was released on 2022 with total page 151 pages. Available in PDF, EPUB and Kindle. Book excerpt: Strain-mediated magnetoelectric composites have received considerable attention due to their multi-physics interaction. The ability to control magnetism at the nanoscale through strain induced electric field have made these composite more energy efficient relative to electric current methods. These strains can also be localized to address individual magnetostrictive nano-elements in an array. These feature have made magnetoelectric composites a potential candidate for magnetic-based devices like cell sorting and memory devices. The work presented in this dissertation provides pathways for these applications. The first part presents an alternative to capture and release of superparamagnetic (SPM) particles using FeGa microstructure on a piezoelectric PMN-PT substrate. This work is complemented with material characterization and micromagnetic-based modeling. The second part introduces a mathematical framework to model highly magnetostrictive thin-films under the influence of large residual stresses. This model was tested and validated with respect to polycrystalline Terfenol-D thin-film. The model also suggests a method to partially demagnetize a micro-scale single-domain, which can be of usefulness in cell sorting applications. The third part introduces a novel design of an epitaxial Terfenol-D memory bit on a piezoelectric substrate. This memory bit is actuated through localized electrodes which trigger an OOP deterministic clocking mechanism. This device can provide non-volatile data storage and energy efficient writing capability. Collectively, the findings in this dissertation are used to explore the influence of crystallinity in the magnetization process of highly magnetostrictive thin-films like FeGa and Terfenol-D. The mathematical framework presented in this dissertation expand on previous micromagnetic models to consider the influence of these nano-crystals. Such tools will be practical in future work involving the design and modeling of these magnetoelectric composites.

Download or read book Controlling Magnetization and Strain at the Micron scale and Below in Strain mediated Composite Multiferroic Devices written by Zhuyun Xiao and published by . This book was released on 2017 with total page 72 pages. Available in PDF, EPUB and Kindle. Book excerpt: Strain-coupled multiferroic heterostructures provide a path to energy-efficient, voltage-controlled magnetic nanoscale devices, a region where current-based methods of magnetic control suffer from Ohmic dissipation. Magnetoelectric coupling behavior in such composite heterostructures has thus been of substantial interest for scientific research and applications. As the dimension of the devices scale down, novel physical phenomenon emerges and thus also requires further understanding of both the magnetization and strain behavior at micro- and nanoscale. When it comes to the magnetization behavior, there has been a growing interest in highly magnetoelastic materials, such as Terfenol-D, prompting a more accurate understanding of their magnetization behavior. To address this need, we simulate the strain-induced magnetization change with two modeling methods: the commonly used unidirectional model and the recently developed bidirectional model. Unidirectional models account for magnetoelastic effects only, while bidirectional models account for both magnetoelastic and magnetostrictive effects. We found unidirectional models are on par with bidirectional models when describing the magnetic behavior in weakly magnetoelastic materials (e.g., Nickel), but the two models deviate when highly magnetoelastic materials (e.g., Terfenol-D) are introduced. These results suggest that magnetostrictive feedback is critical for modeling highly magnetoelastic materials, as opposed to weaker magnetoelastic materials, where we observe only minor differences between the two methods' outputs. To our best knowledge, this work represents the first comparison of unidirectional and bidirectional modeling in composite multiferroic systems, demonstrating that back-coupling of magnetization to strain can inhibit formation and rotation of magnetic states, highlighting the need to revisit the assumption that unidirectional modeling always captures the necessary physics in strain-mediated multiferroics. In terms of the strain behavior, there hasn't been a system-level work that quantifies the strain distribution as a function of the electric field at these so-called mesocales level (100 nm- 10 um), in the range of the constitutive grain size, etc. To obtain mechanical properties at such length scale, including strain information, we used synchrotron polychromatic scanning x-ray diffraction (micro-diffraction) on beamline 12.3.2 at the Advanced Light Source of the Lawrence Berkeley National Lab. With given ferromagnetic and ferroelectric components, it is the magnetoelectric coupling between the two that governs the interaction. In this work, we also demonstrate a method to enhance the coupling behavior between two existing components by interposing a polymer layer.

Download or read book Solution Processed Magnetic and Magnetoelectric Materials for the Development of Future Low Power Devices written by Shreya Kiritbhai Patel and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis, we focus on designing new material systems that could help reduce Ohmic loss to enable future, low-power electro-magnetic devices. The first part of this thesis details voltage-control magnetism, which contrasts to conventional current-controlled magnetism. We specifically investigate strain-mediated magnetoelectric composites, which couple a ferroelectric material that strains in response to a voltage, to a magnetostrictive material, which changes magnetization in response to strain. We introduce a new category of magnetoelectric nanocomposites with residual porosity engineered into them. In the synthesis, block-copolymer templating is used to create a porous ferromagnetic framework, and then atomic layer deposition (ALD) is used to partly coat the inside of the pores with ferroelectric material. Residual porosity increases the mechanical flexibility of the composites, and thus allows for more fully-realized magnetoelectric coupling than conventional layered composites. Thus, we find large (> 50 %) changes in magnetization in samples with the most residual porosity.While the first part of this thesis focuses on making nanostructured magnetoelectric materials, the second part of this thesis discusses our work in building new bulk/thin-film spintronic materials. For the ideal spintronic device material, low magnetic loss and high magnetostriction are desirable, but spin-orbit coupling prevents both from occurring in the same material. Here we study systems based on yttrium iron garnet (YIG), a low magnetic loss material, and dope them to increase their magnetostriction. Using sol-gel chemistry, we surveyed a range of dopant stoichiometries of Ce:YIG and Ru:YIG, and made the exciting discovery that Ru:YIG films actually exhibit lower Gilbert damping than undoped YIG, which has previously been predicted by Kittel. Since inhomogeneous broadening is quite large in these polycrystalline films due to magnon scattering at grain boundaries, we turned to polymer-assisted deposition, a solution-based method that allows for the deposition of epitaxial films. Interestingly, we found that Ru:YIG films grown on (111) GGG exhibited perpendicular magnetic anisotropy, which necessitates high magnetostriction. Furthermore, these films were found to have lower damping than undoped YIG, echoing previous findings in sol-gel films. Thus, we have shown that low-cost solution-phase methods can be used to produce high-magnetostriction, low-magnetic-loss materials for potential spintronic applications.

Download or read book The Effect of Magnetoelectric Coupling and Magnetic Correlations on Temperature and Field driven Transitions in Magnetic and Multiferroic Materials written by Karen L. Livesey and published by . This book was released on 2009 with total page 119 pages. Available in PDF, EPUB and Kindle. Book excerpt: Magnetoelectric coupling and magnetic correlations are shown to affect coupled order parameters, magnetisation M and electric polarisation P, in a multiferroic material. A ferromagnetic ferroelectric system is considered with two types of magnetoelectric coupling (anisotropic and isotropic) which couple P to different magnetic correlations. Using a mean field calculation for anisotropic coupling, it is shown that magnetic fluctuations h(Sz i )2i alter P even for temperatures above the magnetic Curie temperature. For isotropic coupling, a Green's function technique with a Random Phase Approximation is used to calculate how transverse correlations between neighbouring magnetic spins at sites i and j, such as hSx i Sx j i, affect P. The ferroelectric transition temperature and even the order of the transition is altered by the inclusion of magnetic correlations. Thermal hysteresis of the electric polarisation is also shown to exist in this model system. The methods presented can be extended to treat multiferroic systems with more complicated magnetic orderings. Another consequence of magnetoelectric coupling is the hybridisation of magnetic/electric excitations, known as "electromagnons." We show that for a ferroelectric canted antiferromagnet (with a weak ferromagnetic moment) with isotropic magnetoelectric coupling an electromagnon mode exists. When such a material, together with a ferromagnet, form a thin film heterostructure, dipolar coupling between the films allows for the electromagnon frequency to be tuned in the microwave regime. We use an effective medium method that takes into account electromagnetic boundary conditions to find the high frequency susceptibility of such composites and identify the type of resonant modes. However, the magnetoelectric coupling is usually weak through dipolar coupling. Magnetostrictive/piezoelectric composites have been shown to have a much larger strain-mediated magnetoelectric coupling so we detail how the effective medium method can be extended to treat such systems. It has been shown that in magnetostrictive/piezoelectrive composites, electric field can drive a magnetisation reorientation transition. Such electric field control of magnetisation is one of the chief aims in the study of multiferroic materials. However, the dynamics of such an electric field-driven magnetisation reorientation have not been studied as yet, either experimentally or theoretically. As a first step, a study of how nonlinear spin wave processes (or correlations) may alter the dynamics of magnetic field-driven magnetisation reorientation in thin magnetic films is presented here. A classical Hamiltonian formalism is developed to calculate the threshold magnetisation precession angle above which threeand four-wave decay of uniform precession may occur. The analytic results for fourwave scattering are used to qualitatively explain experimental results of the magnetisation coherency during reorientation in 15 nm Ni81Fe19 films. Possible extensions to multiferroic systems are discussed briefly.

Download or read book 1 6 written by and published by . This book was released on 1981 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Deterministic Control of Individual Nanomagnets in Strain mediated Multiferroic Heterostructures written by Jizhai Cui and published by . This book was released on 2016 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt: Controlling magnetism on the nanoscale has attracted considerable research interest for the high potential in non-volatile memory and logic applications. Using strain to control magnetization in strain-mediated multiferroic heterostructures is considered the most energy efficient approach, reducing energy dissipation by orders of magnitude. The strain-mediated multiferroic heterostructure has a ferromagnetic element on a ferroelectric substrate. Applying voltage to the ferroelectric substrate induces piezoelectric strain, which manipulates the magnetization of the ferromagnetic element through magnetoelastic effect. Nanomagnets, as information storage bits for non-volatile memory applications, need to be both individually and deterministically controlled. In the present work, two concepts are developed for this aim, one uses an electrode pattern design on a piezoelectric substrate to produce localized strain, and the other consists of architecting the shape of nanomagnets to take advantage of magnetic shape anisotropy. Patterned electrodes are designed and their effect is modeled using finite element simulations. By selectively applying voltage to electrode pairs, various strain configurations are produced between the electrodes, creating localized strain that controls individual nanomagnets. The modeling results were confirmed by experiments that used magnetization characterization techniques including magneto-optical Kerr effect (MOKE) and magnetic force microscopy (MFM). By architecting the geometric shape, "peanut" and "cat-eye" shaped nanomagnets were engineered on piezoelectric substrates. These nanomagnets undergo repeated deterministic 180? magnetization rotations in response to individual electric-field-induced strain pulses. The designs were modeled using micromagnetics simulations. Both concepts provide significant contributions for next generation strain-mediated magnetoelectric memory research. This work opens a broad design space for next generation magnetoelectric spintronic devices.

Download or read book Magnetoelectric Devices and Multiscale Modeling written by Yu-Ching Hsiao and published by . This book was released on 2022 with total page 81 pages. Available in PDF, EPUB and Kindle. Book excerpt: Multiferroic materials facilitate the novel development of magnetic devices. Extensive effort has been devoted to the multiferroic field to overcome the scaling limitations in past decades. Likewise, this work focused on increasing energy efficiency and density through the applications, development, and fundamental studies of multiferroics. Application such as cell sorting was proposed to resolve the cell aggregation problem of the conventional method through the permanent magnet. Co/Ni multilayers exhibiting perpendicular magnetic anisotropy (PMA) were designed, fabricated, and tested for the cell sorting application. The cell capture method demonstrates a way towards compact lab-on-a-chip devices for more precise cell sorting control. In this study, we observed an inhomogeneous response across these Co/Ni microdevices. This drove us to investigate the roughness and magnetoelectric effects on the magnetic behavior across the microdevices. The homogenous response is critical to reliable strain-mediated multiferroic devices. We fabricated Co/Ni microdisks on the [Pb(Mg1/3Nb2/3)O3]0.7-[PbTiO3]0.3 (PMN-30PT) substrate, and characterized them using magneto-optic Kerr effect (MOKE) method to obtain the coercivity of each individual microdisks. The results were used to study the dependence on roughness and electric field-induced strain in the substrate. This study aimed to assist the reliable design of strain-mediated PMA based devices. Lastly, an atomic model was developed to understand static and dynamic magnetic behaviors using a multiscale modeling approach. Two Co adatoms on a Cu(100) substrate were modeled by incorporating the atomic displacement effects. The parameters used in the model were extracted from the density functional theory (DFT) calculation. Ferromagnetic to antiferromagnetic transition, and in-plane to out-of-plane switching were observed with changes made to the atomic displacement and applied external field. Additionally, the tunability of the resonance frequency of the two-adatom system was demonstrated with the magneto-displacement effect. The outcome shows that the atomic level devices are promising for the potential application of quantum computing and storage devices. When viewed together, the studies provide the foundational tools to develop next-generation multiferroic devices.

Download or read book Magnetoelectric Coupling in Membrane Thin film Heterostructures written by Shane Lindemann and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Strain-coupling in ferromagnetic (FM) / ferroelectric (FE) multiferroic heterostructures shows promise to become the next generation of low-power, ultra-fast memory storage devices in addition to opening new avenues of fundamental scientific research. The relaxor ferroelectric (1-x)Pb(Mg1/3Nb2/3)O3-(x)PbTiO3 (PMN-PT) is an ideal candidate as the FE layer due to its giant piezoelectricity. By coupling with a FM overlayer, an applied bias across the PMN-PT results in the generation of large piezostrains which are transferred into the FM layer to alter the FM's magnetic anisotropy, resulting in a piezo-driven magnetoelectric (ME) effect. This has been demonstrated using bulk single crystals of PMN-PT coupled with FM overlayers, but the bulk dimensions required application of over 100V applied bias. For low power coupling to be achieved, thin films of PMN-PT must be used.Strain-mediated ME coupling in thin film heterostructures has proven to be difficult due to two major challenges: 1) Elastic clamping by the substrate acts to eliminate giant piezoelectricity in PMN-PT thin films. 2) The films must exhibit anisotropic in-plane strain to alter in-plane magnetic anisotropy of a FM overlayer. Our approach to overcome these challenges is through growth of epitaxial thin films of PMN-PT followed by release of the films from their substrate to make ME membranes. After release from the substrate, we observe a recovery of giant piezoelectricity in PMN-PT membranes and demonstrate successful ME coupling with Ni overlayers. We found that for (001) oriented PMN-PT membranes, the nominally isotropic in-plane strains are transformed into anisotropic in-plane strains through Piezotensor Engineering, i.e. an interaction between biased and unbiased regions dictated by the electrode geometry. In (011) PMN-PT membranes, intrinsic anisotropic in-plane strains result in a 90-degree rotation of Ni's in-plane anisotropy with only 3V bias across the PMN-PT, demonstrating that PMN-PT membranes can achieve low power ME coupling. The membrane assembled heterostructures will lead to novel strain-mediated devices through heterogeneous integration. Individual membranes of various materials, including complex oxides, III-V's, and 2-Dimensional (2D) materials, can be stacked together with the PMN-PT membranes providing an exciting pathway to study an extraordinary range of piezo-driven phenomena and functionalities.

Download or read book Engineering of Iron Gallium and Hafnium Oxide Interfaces for Magnetoelectric Applications written by Adrian Acosta and published by . This book was released on 2022 with total page 164 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work focuses on the engineering and tailoring the interfaces of both ferromagnetic multilayer films based on (Iron Gallium) FeGa as well as the surfaces of ferroelectric (Hafnium Oxide) HfO2 for applications toward magnetoelectric applications, which offer the promise of efficient control of magnetism at the nanoscale. In this work, two key materials challenges of the respective ferromagnetic and ferroelectric materials toward integration in composite magnetoelectric devices are discussed: development of ferromagnetic materials with strong magnetomechanical coupling and ferroelectric materials with robust ferroelectric properties at the nanoscale. First, while FeGa is a well-known magnetostrictive material that could be a candidate for integration for strain-mediated magnetoelectric devices, the challenge remains that it is lossy at high frequencies. On the other hand, while ferroelectric HfO2 has gained interest due to its emergent and ferroelectricity at the nanoscale that circumvents traditional limitations of ferroelectric materials and is CMOS compatible, it remains a challenge to fully understand how to stabilize the ferroelectric phase. To address the former, this work investigated how the influence of an underlayer and a multilayering structure can be used to enhance the soft magnetic properties of FeGa films. It was found that a NiFe underlayer serves to influence the microstructure of the FeGa films, resulting in a smaller grain size and enhanced texture, which yielded a smaller coercivity while retaining a strong magnetostriction. It was also observed that the saturation magnetostriction is maintained for the FeGa films. Furthermore, a multilayering strategy that uses NiFe as an interlayer to form FeGa/NiFe bilayers was investigated to achieve a composite with a further decrease in coercivity and lower high frequency losses - specifically for a multilayer consisting of ten bilayers of FeGa (10 nm) / NiFe (2.5 nm). Additionally, the multilayering strategy combined with an insulating interlayer was shown to be a useful strategy to achieve a composite with an even lower coercivity meets the necessary criteria of magnetic softness and low loss necessary for integration in magnetoelastic and high frequency antenna devices. To address the latter, density functional theory was used to understand the relationship between the ferroelectric polarization and the surface composition to stabilize the orthorhombic ferroelectric phase of HfO2. It was found that the surface composition plays a critical role in the ferroelectric stability of orthorhombic HfO2 thin films, which can enable stable polarization without a critical thickness limit under an open-circuit boundary condition. It was found that a relatively oxygen-rich positively polarized surface can effectively screen the polarization to stabilize the orthorhombic phase. In contrast, stoichiometric HfO2 surfaces that cannot screen the polarization lead to an ionic depolarization towards a nonpolar monoclinic phase. This highlights the importance of controlling the surface composition for the stability of ferroelectricity in HfO2 and points towards control of the surface composition as a mechanism for optimizing the ferroelectric performance of HfO2-based thin films. This work provided two routes for the development and engineering of ferromagnetic and ferroelectric materials that can overcome key material challenges for the integration toward magnetoelectric devices with robust and efficient performance.

Download or read book Modeling the Wave Motion in Magneto electro elastic Materials written by Zhengliu Zhou and published by . This book was released on 2017 with total page 120 pages. Available in PDF, EPUB and Kindle. Book excerpt: Strain-mediated magneto-electric materials, also known as magneto-electro-elastic materials, have received tremendous attention due to their potential in realizing electric-field control of magnetism. More importantly, novel wave propagating behavior can be found in such materials, which involves coupling between elastodynamics and electrodynamics. Yet little work has been done on numerical simulations that allow us to look into the wave phenomena in these materials. This dissertation is devoted to the development and validation of finite element methods that are capable of handling this coupling, with an emphasis on the acoustically-driven electromagnetic radiation from piezoelectrics and piezomagnetic media.

Download or read book Mesoscale Interfacial Dynamics in Magnetoelectric Nanocomposites written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Theory and modeling of chessboard-like self-assembling of vertically aligned columnar nanostructures in films has been developed. By means of modeling and three-dimensional computational simulations, we proposed a novel self-assembly process that can produce good chessboard nanostructure architectures through a pseudo-spinodal decomposition of an epitaxial film under optimal thermodynamic and crystallographic conditions (appropriate choice of the temperature, composition of the film, and crystal lattice parameters of the film and substrate). These conditions are formulated. The obtained results have been published on Nano Letters. Based on the principles of the formation of chessboard nanostructured films, we are currently trying to find good decomposing material systems that satisfy the optimal conditions to produce the chessboard nanostructure architecture. In addition we are under way doing 'computer experiments' to look for the appropriate materials with the chessboard columnar nanostructures, as a potential candidate for engineering of optical devices, high-efficiency multiferroics, and high-density magnetic perpendicular recording media. We are also currently to investigate the magnetoelectric response of multiferroic chessboard nanostructures under applied electric/magnetic fields. A unified 3-dimensional phase field theory of the strain-mediated magnetoelectric effect in magnetoelectric composites is developed. The theory is based on the established equivalency paradigm: we proved that by using a variational priciple the exact values of the electric, magnetic and strain fields in a magnetoelectric composite of arbitrary morphology and their coupled magneto-electric-mechanical response can be evaluated by considering an equivalent homogeneous system with the specially chosen effective eigenstrain, polarization and magnetization. These equivalency parameters are spatially inhomogeneous fields, which are obtained by solving the time-dependent Ginzburg-Landau equations. The paper summarizing these results is to be submitted to JAP. We are currently using the computational model based on the unified phase field theory to predict the local and overall response of the magnetoelectric composites with arbitrary configuration under applied fields, and to find the optimal composite microstructure that produces the strongest ME coupling. We have developed modeling and simulations to support Dr. S. Pryia efforts to produce the strongest ME coupling by searching the optimal configuration of applied electric/magnetic fields, and microstructure of polycrystalline multiferroics. An analytical model demonstrates that the optimization of a magnetoelectric (ME) coupling of a laminar magnetic/piezoelectric polycrystalline composite could be obtained by a proper choice of the magnetic and electric poling directions and the directions of the applied a.c. fields. The results have been published on JAP. Our next step is to determine the domain of optimal parameters and configurations by using our optimization theory and computational modeling.