Magnetoelectric Devices Research Articles

Magnetoelectric devices based on magnetoelectric bulk composites

In this review, we summarize the latest developments of bulk structured magnetoelectric (ME) composites and their device applications, with focused investigation into their opportunities, prospects, and challenges for potential applications.

Insights into fluidic endogenous magnetism and magnetic monopoles from a liquid metal droplet machine

Magnetism and magnetic monopoles are among the most classical issues in physics. Conventional magnets are generally composed of rigid materials and may face challenges in extreme situations. Here, as an alternative to rigid magnets, we propose, for the first time, the generation of fluidic endogenous magnetism and construct a magnetic monopole through tuning with a liquid metal machine. Based on theoretical interpretation and conceptual experimental observations, we illustrate that when liquid metals, such as gallium alloy, in a solution rotate under electrical actuation, they form an endogenous magnetic field inside. This explains the phenomenon where two such discrete metal droplets can easily fuse together, indicating their reciprocal attraction via the N and S poles. Furthermore, we reveal that a self-fueled liquid metal motor also runs as an endogenous fluidic magnet owing to the electromagnetic homology. When aluminum is added to liquid gallium in solution, it forms a spin motor and dynamically variable charge distribution that produces endogenous magnetism inside. This explains the common phenomena where reflective collision and attractive fusion between running liquid metal motors occur, which are partially caused by the dynamic adjustment of their N and S polarities, respectively. On this basis, more experimental approaches capable of generating dynamic electrical fields also work for the same target. Finally, we propose that such a fluidic endogenous magnet could lead to a magnetic monopole and four technical routes to realize this are suggested. The first involves matching the interior flow of liquid metal machines. The second is the superposition between an external electric effect and the magnetic field. The third route involves composite construction between magnetic particles and a liquid metal spin motor. Finally, chemical methods, such as via galvanic cell reactions, are proposed. Overall, the present theory and identified experimental evidence illustrate the role of a liquid metal machine as a fluidic endogenous magnet and highlight promising methods for the realization of magnetic monopoles. A group of unconventional magnetoelectric devices and applications could therefore be possible in the near future.

Synthesis and characterization of single pervoskite Ba(Ni1/3Mn1/3W1/3)O3

Single perovskite oxide materials have very attractive behaviors like multiferroics, piezoelectricity as well as dielectric and ferromagnetic properties. Owing to these properties, perovskites can be used widely in many applications, such as ferroelectric and magnetic random access memories, transducers, sensors, actuators and also in magneto-electric spintronic devices. In this research, a novel and lead-free multiferroic material Ba(Ni1/3Mn1/3W1/3)O3 pervoskite is chemically prepared by cost effectual solid-state reaction method by taking oxides of Ba, Ni, Mn and W. X-ray diffraction, SEM, EDAX and the dielectric behaviors (like dielectric_permittivity, tanδ, dielectric_modulus, impedance and electrical_conductivity) of the above composites are analyzed.

Magnetoelectric Coupling in Bismuth Ferrite—Challenges and Perspectives

Multiferroic materials belong to the sub-group of ferroics possessing two or more ferroic orders in the same phase. Aizu first coined the term multiferroics in 1969. Of late, several multiferroic materials’ unique and robust characteristics have shown great potential for various applications. Notably, the coexisting magnetic and electrical ordering results in the Magnetoelectric effect (ME), wherein the electrical polarization can be manipulated by magnetic fields and magnetization by electric fields. Currently, more significant interests lie in significantly enhancing the ME coupling facilitating the realization of Spintronic devices, which makes use of the transport phenomenon of spin-polarized electrons. On the other hand, the magnetoelectric coupling is also pivotal in magnetic memory devices wherein the application of small electric voltage manipulates the magnetic properties of the device. This review gives a brief overview of magnetoelectric coupling in Bismuth ferrite and approaches to achieve higher magnetoelectric coupling and device applications.

Magnetoelectric Effect in Dipolar Clusters.

We combine the anisotropy of magnetic interactions and the point symmetry of finite solids in the study of dipolar clusters as new basic units for multiferroics metamaterials. The Hamiltonian of magnetic dipoles with an easy axis at the vertices of polygons and polyhedra, maps exactly into a Hamiltonian with symmetric and antisymmetric exchange couplings. The last one gives rise to a Dzyaloshinskii-Moriya contribution responsible for the magnetic modes of the systems and their symmetry groups, which coincide with those of a particle in a crystal field with spin-orbit interaction. We find that the clusters carry spin current and that they manifest the magnetoelectric effect. We expect our results to pave the way for the rational design of magnetoelectric devices at room temperature.

Anisotropy of magnetoelectric effects in an amorphous ferromagnet-piezoelectric heterostructure

In-plane anisotropy of linear and nonlinear magnetoelectric (ME) effects in a heterostructure composed of mechanically coupled layers of amorphous iron-based ferromagnet and piezoelectric lead zirconate-titanate ceramics has been investigated. The measurements were performed on a disk-shaped sample subjected to a low-frequency excitation magnetic field h oriented either parallel or perpendicular to a bias magnetic field H0. The first harmonic of the voltage response was recorded in the case of the linear ME effect, which was excited at frequencies of acoustic resonances of the sample, and the second harmonic in the case of the nonlinear ME effect excited in the non-resonance regime. Strong uniaxial or biaxial anisotropy for different directions of the bias field within the sample plane was observed. The uniaxial anisotropy of the ME effect occurs due to the uniaxial magnetic and magnetostrictive anisotropy of the amorphous ferromagnetic layer that is a result of its fabrication by the ultrafast cooling method. The biaxial anisotropy at resonant frequencies is the manifestation of the spatial structure of the excited acoustic modes. The anisotropy of ME effects should be taken into account when developing magnetoelectric devices based on composite heterostructures.

Monolayer Vanadium-Doped Tungsten Disulfide: A Room-Temperature Dilute Magnetic Semiconductor.

Dilute magnetic semiconductors (DMS), achieved through substitutional doping of spin‐polarized transition metals into semiconducting systems, enable experimental modulation of spin dynamics in ways that hold great promise for novel magneto–electric or magneto–optical devices, especially for two‐dimensional (2D) systems such as transition metal dichalcogenides that accentuate interactions and activate valley degrees of freedom. Practical applications of 2D magnetism will likely require room‐temperature operation, air stability, and (for magnetic semiconductors) the ability to achieve optimal doping levels without dopant aggregation. Here, room‐temperature ferromagnetic order obtained in semiconducting vanadium‐doped tungsten disulfide monolayers produced by a reliable single‐step film sulfidation method across an exceptionally wide range of vanadium concentrations, up to 12 at% with minimal dopant aggregation, is described. These monolayers develop p‐type transport as a function of vanadium incorporation and rapidly reach ambipolarity. Ferromagnetism peaks at an intermediate vanadium concentration of ~2 at% and decreases for higher concentrations, which is consistent with quenching due to orbital hybridization at closer vanadium–vanadium spacings, as supported by transmission electron microscopy, magnetometry, and first‐principles calculations. Room‐temperature 2D‐DMS provide a new component to expand the functional scope of van der Waals heterostructures and bring semiconducting magnetic 2D heterostructures into the realm of practical application.

Exploring magnetoelectric coupling in trilayer [Ba(Zr0.2Ti0.8)O3- 0.5(Ba0.7Ca0.3)TiO3]/ CoFe2O4/[Ba(Zr0.2Ti0.8)O3- 0.5(Ba0.7Ca0.3)TiO3] thin film

Magnetoelectric (ME) heterostructures with strong ME coupling at room temperature are of great importance due to their promising applications in next-generation devices. Here, lead-free [Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3]/CoFe2O4/[Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3] (abbreviated as (BZT-0.5BCT)/CFO/(BZT-0.5BCT)) trilayer thin film has been deposited on Pt/Ti/SiO2/Si (100) substrate by pulsed laser deposition technique. Dielectric properties of trilayer thin film show the relaxor behavior and high value of dielectric constant (∼2.2 × 103) with low dielectric loss (∼0.16) at frequency 100 Hz at room temperature. Typical ferroelectric and magnetic hysteresis loops were found with large electric polarizations (Ps = 12.14 μC/cm2, Pr = 6.0 μC/cm2) and magnetization (Ms = 246 emu/cc and Mr = 66.6 emu/cc), respectively. The change in PE loop on the application of magnetic field represents the strong ME coupling. The high value of ME coefficient (αME∼0.74 V/cm.Oe) was detected at room temperature which indicates its potential application for multifunctional ME devices.

Large converse magnetoelectric effect in Sm doped Pb(Mg1/3Nb2/3)-PbTiO3 and NiFe2O4 laminate composite

The magnetoelectric bilayer composite Sm-doped Pb(Mg1/3Nb2/3)-PbTiO3/NiFe2O4 (Sm:PMN-PT/NFO) developed in this study exhibits a converse magnetoelectric coefficient (αCME) of 0.34 G cm/V at resonance. This value is at least an order of magnitude higher than any previously reported αCME for polycrystalline ferrite-based laminate composites. The large CME coefficients in both dc- and self-biased modes are attributed to the high transverse piezoelectric coefficient (d31 ∼ −421 pC/N) of the piezoelectric phase Sm:PMN-PT. High converse magnetoelectric coefficient and characteristic advantages of ferrite-based magnetoelectric (ME) materials such as low eddy current losses make this composite a potential candidate for the ME devices operating in the converse mode. In particular, its performance characteristics for two applications —voltage to current converter, and as a magnetic switch —have been investigated. The laminate composite exhibits current to voltage conversion performance of 14 mA/V at the resonance frequency. The performance characteristics as a magnetic switch show that the bi-stable states separated by 25 G can be realized through an AC signal of 5V.

Multiferroic thin film via SrRuO3–BaTiO3 vertically aligned nanocomposite design

The design of a nanocomposite system with a ferroelectric phase and a ferromagnetic phase is essential to achieve multiferroics due to the limited one-phase multiferroic material in nature. Ferromagnetic SrRuO3 (SRO) and ferroelectric BaTiO3 (BTO) have been selected to achieve the SRO-BTO nanocomposite thin film. The film exhibits excellent crystal quality owing to the perfect lattice matching of both phases with the SrTiO3 substrate, and very thin SRO nanopillars (∼5 nm) have been obtained. Because of the anisotropic nature of the SRO nanopillars, magnetic anisotropy has been obtained for the nanocomposite thin film, and the Curie temperature (Tc) can be determined to be 152 K. Furthermore, switchable piezoelectric behavior of the nanocomposite film with a maximum d33 value of ∼70 pm/V is obtained by the piezoelectric force microscopy measurement. Overall, the SRO-BTO nanocomposite system presents the desirable multiferroic response, which is promising for future magnetoelectric device integration.

Understanding the Switching Mechanisms of the Antiferromagnet/Ferromagnet Heterojunction

Electric-field-driven spintronic devices are considered promising candidates for beyond CMOS logic and memory applications thanks to their potential for ultralow energy switching and nonvolatility. In this work, we have developed a comprehensive modeling framework to understand the fundamental physics of the switching mechanisms of the antiferromagnet/ferromagnet heterojunction by taking BiFeO3/CoFe heterojunctions as an example. The models are calibrated with experimental results and demonstrate that the switching of the ferromagnet in the antiferromagnet/ferromagnet heterojunction is caused by the rotation of the Neel vector in the antiferromagnet and is not driven by the unidirectional exchange bias at the interface as was previously speculated. Additionally, we demonstrate that the fundamental limit of the switching time of the ferromagnet is in the subnanosecond regime. The geometric dependence and the thermal stability of the antiferromagnet/ferromagnet heterojunction are also explored. Our simulation results provide the critical metrics for designing magnetoelectric devices.

Large magnetodielectric effect based on spin-dependent charge transfer in metal–insulator type Co-(BaF2) nanogranular films

Cobalt-metal-fluoride nanogranular films exhibit high electrical resistivity (ρ) and high permittivity (ɛ′) as well as high magnetic moments, making them potentially suitable for applications in low power magnetoelectronic devices at a high-frequency range. Here, we present the DC/AC magnetoelectric effect of high-ρ Cox-(BaF2)1 − x nanogranular films that are constituted of Co nanogranules of about 2 nm in diameter in an insulating BaF2 crystal. Under the application of magnetic field (H), we observed the ρ variations (Δρ/ρ0) of 2.0%–5.9% for x ranging 0.19–0.54 and the ɛ′ variations (Δɛ/ε0′) of 0.7%–6.0% for x ranging 0.19–0.42, respectively. These magnetically controllable ρ and ɛ′ are realized based on the spin-dependent quantum-mechanical charge transfer. The Cox-(BaF2)1 − x film for x = 0.42 possesses high ρ, while remaining in a notably high Δɛ/ε0′ of 6% at a megahertz frequency range. This study demonstrates a candidate of high-resistive magnetoelectric nanogranular films, which may bring prosperous applications in high-frequency magnetoelectric devices with low power consumption.

Torsional modes in the magnetoelectric effect for a two-layer ferrimagnet-piezoelectric YIG / GaAs structure

The article is devoted to the theoretical study of the magnetoelectric (ME) effect in the magnetostrictive-piezosemiconductor structure of yttrium iron garnet (YIG) - gallium arsenide (GaAs) in the torsional mode. Earlier, it was found that the ME effect significantly increases with the transition from the low-frequency range to the region of electromechanical resonance (EMR). There are known results on the study of the ME effect in the range of different EMR modes: planar, flexural, and shear. This article proposes to consider the ME effect in the torsional mode region in a layered YIG-GaAs composite. Interest in this phenomenon is associated both with the study of the newest effect, and with the possibility of studying the ME effect in the region of magnetoacoustic resonance, i.e. when the torsional mode coincides with the spin wave in the region of ferromagnetic resonance. The results obtained can find application in the design of new ME devices.

Coexistence of two ferroelectric phases and improved room-temperature multiferroic properties in the (0.70)BiFe1 − xCoxO3–(0.30)PbTiO3 system

In the present time, the focus of many researchers is to enhance the multiferroic properties of pure and doped BiFeO3 (BFO) based materials. However, the materials community has not yet achieved the desired multiferroic properties in single doped BiFeO3. Therefore, we decided to start with the well known system BiFeO3–PbTiO3, with good ferroelectric properties, as compared to undoped BFO and Co2+ as dopant, to obtain the (0.70)BiFe1 − xCoxO3–(0.30)PbTiO3 system. In this paper, the structural, magnetic, and ferroelectric properties of (0.70)BiFe1 − xCoxO3–(0.30)PbTiO3, with 0.00 ≤ × ≤ 0.12, prepared by a simple solgel route is presented. The inclusion of Co2+ leads to notable changes in the structural and magnetic properties. X-ray diffraction studies revealed that the samples crystallize into two ferroelectric phases: rhombohedral (R3c) and tetragonal (P4mm) up to x = 0.06; afterward, it leads to nearly a single phase tetragonal structure for x = 0.09 and 0.12. The magnetic properties are enhanced in a significant manner with Co2+ doping and are ascribed to structural changes (change in Fe–O–Fe bond length) and the suppression of the spiral spin structure characteristic of BiFeO3. The theoretical analysis of the magnetic data shows that the ferromagnetic part also increases with Co2+ doping. Ferroelectric properties are also enhanced with Co doping due to a decrease in the DC current density. The observed room temperature multiferroic properties of this compound foresee great potential for magnetoelectric devices.

Magnetoelectric coupling in terbium doped particulate multiferroic composites based on BaTiO3–CoFe2O4

The present study attempts to enhance the coupling by rare-earth doping in particulate multiferroic composites of BaTiO3 and CoFe2O4. These composites were prepared by conventional solid-state route with the compositions (1-x) Ba0·99Tb0·02Ti0·99O3 – x Co0·94Tb0·06Fe2O4 (x = 0.02, 0.04 and 0.06). The decrease in cell volume of Co0·94Tb0·06Fe2O4 phase with the increase in Co0·94Tb0·06Fe2O4 phase results in the enhancement of strain, which in turn improves the coupling. The Tb3+ ion doping enhances the dielectric constant of composites and the Curie Weiss Law shows the diffused nature of ferroelectric phase transitions. The unification of two ferroic phases in composites has been confirmed by tracing the P-E and M − H hysteresis loops. The P-E loops are free from leakage currents and M − H loops are well saturated, confirming an ordered domain structure. The terbium doping results in high magnetoelectric coupling coefficients, so making these composites as potential candidates for magnetoelectric devices.

Improving electric field controlled magnetism of micron-scale-thickness Fe71Ga17B12 film on Pb(Mg1/3Nb2/3)0.7O3-PbTi0.3O3 by multilayer preparation method

Enhancing electric field controlled magnetism of micron-scale-thickness ferromagnetic film is of great significance to improve the performance of magnetoelectric (ME) sensors, ME tunable inductors and other ME devices. In order to achieve above purpose, multilayer preparation method was proposed and validated by experiment studies on multilayer (Cu(10 nm)/(FeGaB(100 nm)/Cu(5 nm))10) and monolayer (Cu(10 nm)/FeGaB (1000 nm)/Cu(5 nm)) samples, respectively. The results show the electric field controlled magnetism could be enhanced obviously by the multilayer preparation method. Meanwhile, the finite element simulation model was established to analyze possible causes for the improvement of electric field controlled magnetism in multilayer sample. The model revealed that multilayer preparation can reduce the in-plane demagnetizing factor and increase the internal magnetic field of the magnetic materials, thus enhancing electric field controlled magnetism. This work is conducive to the development of micron-scale-thickness films in electric field control of magnetism, which contributes to the application of ferroelectric/ferromagnetic heterostructures in ME devices.

In-Plane Sizes Effects on Magnetoelectric Characteristics of a Ni-PZT Planar Heterostructure

Nowadays, the size reduction of electronic devices based on magnetoelectric (ME) effects is an important task. This will provide an opportunity for the wide integration of ME devices into modern microsystem technology. In this letter, the effects of in-plane sizes of planar heterostructures containing a ferromagnetic Ni film and a piezoelectric lead zirconate titanate (PZT) substrate on characteristics of the direct resonance ME effect are investigated. The Ni films of 10 μm in thickness were electrodeposited on the PZT substrates that were 200-μm-thick and 1.2-23 mm in length. The structures were placed in a permanent magnetic field and excited with an ac magnetic field. The generated ME voltage was measured at frequencies near planar acoustic resonances of the structures. For a 1.2 mm long structure, a frequency of 1380 kHz for in-plane acoustic resonance was achieved. A drop in the amplitude of the ME voltage was observed when the length of the structure became less than a critical value. Various mechanisms are discussed that lead to a voltage drop with a reduction of sizes of the structure, including the demagnetization effect, relaxation losses due to frequency dependence of the capacitance and resistance of the PZT layer, and an increase in acoustic losses.

Magnon-tuning non-volatile magnetic dynamics in a CoZr/PMN-PT structure

Magnon-tuning non-volatile magnetic dynamics is investigated in a CoZr/PMN-PT structure by measuring ferromagnetic resonance at room temperature. The electric-field control of ferromagnetic resonance shows loop-like behavior, which indicates non-volatile electric-field control of the magnetism. Further, fitting the curves of in-plane rotating angle versus ferromagnetic resonance field under different electric fields shows that the effective magnetic field changes in loop-like manner with the electric field. The resulting change in non-volatile saturation magnetization with electric field is consistent with that of a polarization electric field curve. A 1.04% change of saturation magnetization is obtained, which can be attributed to a magnon-driven magnetoelectric coupling at the CoZr/PMN-PT interface. This magnon-driven magnetoelectric coupling and its dynamic magnetic properties are significant for developing future magnetoelectric devices.

Large tunneling magneto-dielectric enhancement in Co(Fe)−MgF2 granular films by minor addition of Si

We report a large enhancement of the tunneling magneto-dielectric (TMD) effect in Co−MgF2 granular films induced by doping using a small amount of Si. This minor addition of Si is dispersed uniformly in the MgF2 matrix and acts by inhibiting the interdiffusion between the Co and MgF2 phases, thus enhancing the magnetization when compared with the case of the corresponding undoped Co−MgF2 films; this consequently results in a greatly enhanced peak dielectric variation (TMD ratio, Δε′/ε′), as indicated by theoretical fittings. Extension of this Si doping effect to CoFe−MgF2 films led to a record-high Δε′/ε′ of 4.3% at 10 kHz and 8.5% at 200 kHz under the application of a magnetic field (H) of 10 kOe, while remaining as high as 2.1% even under H = 1 kOe. This study presents a simple but highly effective approach to enhance the TMD effect in granular nanocomposites, thus opening up the prospect of development of high-performance magnetoelectric devices.

Flash flood simulation and valve behavior of Mytilus galloprovincialis measured with Hall sensors.

Mussels close their shell as a protective strategy and the quantification of this behavioral marker may represent an alarm signal when they are exposed to environmental stressors. In the present study, we investigated the ability of the Mediterranean mussel Mytilus galloprovincialis to recover and then the resilience or inertia of valve activity after a pulsing exposition to diverse levels of salinity (5, 10, 20, and 35 PSU as reference value). The trial simulated an event of drastic and sudden reduction of seawater salinity thus mimicking an event of flash flood from intense rain. Valve gaping and movements were measured in continuous cycle for 10 days using a customized magneto-electric device which uses Hall sensors. Results showed that under normal conditions of salinity (35 PSU), the general pattern of valve movements was a continuously open state with sporadic spikes indicating a closing motion. At salinity of 5, PSU mussels reacted by closing their valves, leading to a 77% mortality on the 4th day. At salinity of 10, PSU animals were observed with closed valves for the entire duration of the exposure and no mortality occurred, they showed a significant reduction in the valve activity once the reference value of salinity was re-established. In contrast, salinity of 20 PSU did not trigger a significant behavioral response. Interestingly, there no define rhythms of valve movements were recorded during salinity challenges.