› › Controlling Magnetization And Strain At The Micron Scale And Below In Strain Mediated Composite Multiferroic Devices

Controlling Magnetization and Strain at the Micron-scale and Below in Strain-mediated Composite Multiferroic Devices

Author : Zhuyun Xiao

Publisher :

Page : 72 pages

File Size : 16,30 MB

Release : 2017

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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.



Strain-mediated Multiferroics Heterostructures for Life Science Applications

Author : Zhuyun Xiao

Publisher :

Page : 223 pages

File Size : 11,32 MB

Release : 2021

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Magnetism is a workhouse for electric power generation at the macroscale, responsible for a large fraction of the electricity generation today. However, conventional approaches to energy conversion using magnets fail at a small scale due to Joule heating from electric currents. Recently, a method has emerged - room-temperature composite multiferroics coupling electrics and magnetics - that allows for control of magnetism via voltage as opposed to current. With this newfound capability, industrial & commercial application spaces are rapidly opening up for domains, including ultra-low-power spintronics devices, microwave devices, and even magnetic particle and cell sorting platforms. Meanwhile, personalized medical therapies hold the potential of new forms of highly effective therapies. One example of personalized medicine is CAR T-cell therapy, which uses patients' cells for cancer treatments. However, such an approach requires technology that can analyze and sort these cells in high quantity, selecting only the cells that will be the most effective cancer fighters. Magnetic cell sorting is a popular approach for high throughput cell sorting. Still, there is no current method capable of capturing and culturing arrays of cells and then selectively releasing the desired ones. Recent advances in room-temperature multiferroic devices, such as devices where magnetism is controlled by electric fields, provide a path for capture, culture, and selective release of cells. However, work remains to understand how to manipulate the magnetic structures that capture these cells. This work aims to develop a multiferroics-based cell manipulation platform with high scalability and can achieve cell control locally. This work first conducts an in-depth study of the magnetization and multiferroic properties of various magnetostrictive layers, including Ni, FeGa, Ni/CoFeB, and Terfenol-D micromagnets on Pb(Mg1/3Nb2/3)O3]0.69[PbTiO3]0.31 (PMN-PT) piezoelectric substrates. It then selects the highly magnetostrictive Terfenol-D micromagnets in the same size scale as human cells as the candidate for life science applications. It also investigates the interaction between these micromagnets and cells before and after a voltage is applied across the PMN-PT substrate. The key questions addressed include how to create structures from a magnetoelastic material that are in the same size scale as human cells (20 \mu m) and control the magnetization of these structures to release cells on-demand via electric fields. Furthermore, this work demonstrates the potential of using patterned surface electrodes to generate localized strain in order to control the behavior of the micromagnets both locally and selectively.



ON STRAIN-MEDIATED MAGNETOELEC

Author : Haitao Chen

Publisher : Open Dissertation Press

Page : 150 pages

File Size : 27,36 MB

Release : 2017-01-26

Category : Technology & Engineering

ISBN : 9781361000502

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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



Strain and Charge Co-mediated Magnetoelectric Coupling in Thin Film Multiferroic Heterostructures

Author : Xinjun Wang

Publisher :

Page : 87 pages

File Size : 34,25 MB

Release : 2015

Category : Ferromagnetic materials

ISBN :

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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.



Voltage Control of Perpendicular Magnetization in Multiferroics

Author : Qianchang Wang

Publisher :

Page : 238 pages

File Size : 20,17 MB

Release : 2018

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Magnetic memory has attracted substantial interest due to its non-volatility and zero power dissipation in stand-by mode. The key of magnetic memory is deterministic control of magnetic bits, especially those with perpendicular magnetic anisotropy (PMA), which have higher thermal stability and smaller footprint compared to in-plane memory bits. Among all the magnetization control mechanism, the strain-mediated multiferroics has surprisingly high energy efficiency (1-3 orders of magnitude better) compared to the other mechanisms using nanoscale magnetization control. The strain-mediated multiferroic control employs a piezoelectric/magnetoelastic heterostructure. To write the magnetic memory, a voltage pulse is applied to the piezoelectric substrate and the induced mechanical strain is transferred to a magnetic element attached to the piezoelectric substrate causing magnetization rotation due to the magnetoelastic effect. The magnetization change can be read out using a magnetic tunnel junction (MTJ). Using strain-mediated multiferroics to control in-plane magnetization has been successfully demonstrated both numerically and experimentally. However, there is little work on using strain-mediated multiferroics to control perpendicular magnetization. In this dissertation, we provide a thorough study on strain-mediated perpendicular magnetization control, including modeling, experiments, and several new device concepts that extend beyond the traditional memory applications. In Chapter 1, we briefly introduce the memory hierarchy and present non-volatile memory technologies, including magnetic memory. We compare the strain-mediated multiferroic magnetization control with other popular control mechanisms. We also describe the simulation basics, micro-fabrication processes, and characterization techniques for the strain-mediated multiferroics. In Chapter 2, we focus on the simulation of strain-mediated perpendicular magnetization control. Three systems are investigated: 1) single nanodot with constant voltage actuation, 2) multiple nanodots coupled by dipole interaction, 3) single nanodot with AC voltage actuation. In Chapter 3, we focus on the experimental investigation of strain-mediated perpendicular magnetization control. Micro-scale magnetic devices are fabricated with two kinds of piezoelectric substrate: PMN-PT bulk and PZT thin film. By analyzing the test results, the challenge and limitation of multiferroic control of perpendicular magnetization are identified. Empirical experiences are summarized to help guide future multiferroic device design. In Chapter 4, we examine a hybrid strain and spin-orbit torque control mechanism. Two models are developed to simulate the hybrid system and surprisingly interesting phenomena are observed. Using the simulation capabilities developed, we propose several new devices that are go beyond standard memory applications. Finally the last chapter summarizes the contents of this dissertation.



Strain-Mediated Magnetoelectric Composites for Cell Sorting and Memory Devices

Author : Michael Guevara De Jesus

Publisher :

Page : 151 pages

File Size : 38,43 MB

Release : 2022

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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.



Controlling the Magnetic State of Nickel Nanocrystal in Granular Multiferroic Composites

Author : Stephen Shinjiro Sasaki

Publisher :

Page : 105 pages

File Size : 10,13 MB

Release : 2018

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Multiferroics are a broad class of materials, which couple multiple ferroic ordering parameters into a single composite--e.g., coupling ferroelectric and ferromagnetic materials. The key feature of multiferroic composites is the ability to control the magnetic (dipole) moments of the composite via an applied electric (magnetic) field. Depending on the coupling mechanisms between the two ferroic materials and the choice of materials, the properties of the multiferroic composite can differ wildly--permitting widespread applications such as field sensors, power convertors, energy storing systems, cooling devices, memory systems, etc. Adding to the plethora of multiferroics, we will be focusing on granular multiferroics (GMF), which substitutes the ferromagnetic material with ferromagnetic nanocrystals, referred to as grains Although only the size of the ferromagnetic material is being changed, GMF composites present new experiments and insights in controlling magnetism at the nanoscale. We use solution processed methods to synthesize superparamagnetic Ni nanocrystals for all of our GMF composites. We developed fabrication methods for strain-mediated GMF composites by employing the reactive Ni nanocrystal surface to bond to a PMN-PT piezoelectric substrate. The magnetic anisotropy of the strain-mediated GMF composite was shown to be controllable and reversible by applying an electric field induced piezoelectric strain. Because the PMN-PT cut used has a biaxial strain, compressive and tensile, we were able to observe inverse magnetic trends for the blocking temperature of the nanocrystal along the two strain axes. Other fabrication methods we developed, modified the nanocrystal surface with diacid ligands to study magnetic interparticle interactions, known as exchange coupling. Theoretical models of exchange coupled GMF composites predicted a novel magnetoelastic coupling mechanisms that can control the magnetic anisotropy of the ensemble by tuning the dielectric environment of the nanocrystal composite. Experimental work was carried out to fabricate and validate this exchange coupled GMF composite, making it the first demonstration of its kind. This thesis outlines our contributions to the ever-growing field of GMF by establishing methods for fabricating novel granular multiferroic composites and evaluating their unique coupling mechanism and magnetic properties.



Multiferroic Devices for Cell Manipulation and Acoustic Resonators

Author : Ruoda Zheng

Publisher :

Page : 0 pages

File Size : 33,36 MB

Release : 2023

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Microscale magnetic devices have garnered significant attention due to their non-volatility, which is the result of energy stored in the spinning of electrons. The key to operating magnetic devices is to control the magnetization, and among all the mechanisms, the strain-mediated multiferroics approach is particularly energy efficient. This approach uses a piezoelectric-magnetoelastic heterostructure, where an input voltage is applied on a piezoelectric thin film to actuate an acoustic response. This film is coupled with magnetostrictive elements, so the induced strain reorients the magnetization vector. This reorientation is currently widely used for storing information like in memory applications. In this dissertation, it will be explored for other applications such as controlling magnetic beads for cell manipulation and producing an electromagnetic signal as an acoustically actuated antenna.Chapter 1 introduces the concept of multiferroics and the theoretical foundations required for analysis and design. Techniques will be presented for both simulation and fabrication aspects. Several published papers on relevant topics will be reviewed. These works indicate that the multiferroics approach has great potential for achieving energy efficiency and miniaturization. Chapter 2 focuses on the magnetic device's use in a cell manipulation application. A design for a magnetically activated cell sorting device is proposed, and the analytical and experimental work involved is described in detail. A multiphysics finite element model was built in order to estimate the time-dependent magnetic forces and the movement trajectory of the cells. This model was used to design the device after verifying its accuracy against experimental values. Three different designs are investigated: (1) a single magnet for cell manipulation, (2) a single magnet for individual cell manipulation, and (3) an array of magnets for individual cell manipulation. The final array design is able to individually control each magnet to individually capture or release a single cell as required for time-dependent post processing. Chapter 3 focuses on the use of multiferroics in an acoustically actuated antenna application. A design is proposed and all analytical and experimental work involved is described in detail. The device is based on magnetoelectric coupling and operates at acoustic resonance in a standing shear bulk wave mode. The methodology for combining the device's micromagnetic, solid mechanics, and electromagnetic behavior is discussed. Multiphysics models are built in order to estimate the mechanical and magnetization response in both transmission and reception modes for the proposed design. The radiation of the magnetic material, the piezoelectric substrate, and the parasitic effects of the wires are investigated. The fabricated device successfully demonstrates mechanical resonance and magnetoelectric coupling. The results show the device's potential for miniaturization and its promise for future compact antenna design. Finally, Chapter 4 summarizes the contents and the main results of the dissertation.



Solution-Processed Magnetic and Magnetoelectric Materials for the Development of Future Low-Power Devices

Author : Shreya Kiritbhai Patel

Publisher :

Page : 0 pages

File Size : 30,71 MB

Release : 2023

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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.



Multiferroics

Author : Andres Cano

Publisher : Walter de Gruyter GmbH & Co KG

Page : 538 pages

File Size : 35,17 MB

Release : 2021-06-21

Category : Science

ISBN : 3110581043

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Book Description

Multiferroics, materials with a coexistence of magnetic and ferroelectric order, provide an efficient route for the control of magnetism by electric fields. The authors cover multiferroic thin-film heterostructures, device architectures and domain/interface effects. They critically discuss achievements as well as limitations and assess opportunities for future applications.