Magnetoelectric effects in multiferroic laminated plates with imperfect interfaces

Two-dimensional （2D） equations for multiferroic （MF） laminated plates with imperfect interfaces are established in this paper. The interface between two adjacent sublayers, which are not perfectly bonded together, is modeled as a general spring-type layer. The mechanical displacements, and the electric and magnetic potentials of the two adjacent layers are assumed to be discontinuous at the interface. As an example, the influences of imperfect interfaces on the magnetoelectric （ME） coupling effects in an MF sandwich plate are investigated with the established 2D governing equations. Numerical results show that the imperfect interfaces have a significant impact on the ME coupling effects in MF laminated structures.

Strain-mediated magnetoelectric control of tunneling magnetoresistance in magnetic tunneling junction/ferroelectric hybrid structures

Because of the wide selectivity of ferromagnetic and ferroelectric(FE)components,electric-field(E-field)control of magnetism via strain mediation can be easily realized through composite multiferroic heterostructures.Here,an MgO-based magnetic tunnel junction(MTJ)is chosen rationally as the ferromagnetic constitution and a high-activity(001)-Pb(Mg_(1/3)Nb_(2/3))_(0.7)Ti_(0.3)O_(3)(PMN-0.3PT)single crystal is selected as the FE component to create a multiferroic MTJ/FE hybrid structure.The shape of tunneling magnetoresistance(TMR)versus in situ E-fields imprints the butterfly loop of the piezo-strain of the FE without magnetic-field bias.The E-field-controlled change in the TMR ratio is up to-0.27%without magnetic-field bias.Moreover,when a typical magnetic field(~±10 Oe)is applied along the minor axis of the MTJ,the butterfly loop is changed significantly by the E-fields relative to that without magnetic-field bias.This suggests that the E-field-controlled junction resistance is spin-dependent and correlated with magnetization switching in the free layer of the MTJ.In addition,based on such a multiferroic heterostructure,a strain-gauge factor up to approximately 40 is achieved,which decreases further with a sign change from positive to negative with increasing magnetic fields.This multiferroic hybrid structure is a promising avenue to control TMR through E-fields in low-power-consumption spintronic and straintronic devices at room temperature.

Magnetoelectric coupling effect of polarization regulation in BiFeO_(3)/LaTiO_(3)heterostructures

An effective regulation of the magnetism and interface of ferromagnetic materials is not only of great scientific significance,but also has an urgent need in modern industry.In this work,by using the first-principles calculations,we demonstrate an effective approach to achieve non-volatile electrical control of ferromagnets,which proves this idea in multiferroic heterostructures of ferromagnetic La TiO_(3)and ferroelectric Bi FeO_(3).The results show that the magnetic properties and two-dimensional electron gas concentrations of La TiO_(3)films can be controlled by changing the polarization directions of Bi FeO_(3).The destroyed symmetry being introduced by ferroelectric polarization of the system leads to the transfer and reconstruction of the Ti-3 d electrons,which is the fundamental reason for the changing of magnetic properties.This multiferroic heterostructures will pave the way for non-volatile electrical control of ferromagnets and have potential applications.

Nonvolatile control of transport and magnetic properties in magnetoelectric heterostructures by electric field

Nonvolatile manipulation of transport and magnetic properties by external electric field is significant for information storage. In this study, we investigate the electric field control of resistance and magnetization in a magnetoelectric heterostructure comprising an electronic phase-separated La0.325Pr0.3Ca0.375MnO3（LPCMO） thin film and a ferroelectric（011）-oriented 0.7Pb（Mg1/3Nb2/3）O3-0.3PbTiO3（PMN-PT） substrate. In a room-temperature poled sample, the metal-toinsulator transition temperature of an LPCMO film increases and the resistance decreases with variation in the effect of the remnant strain. Meanwhile, the increase in the magnetization of the sample is observed as well. This effect would be beneficial for the development of novel storage devices with low power consumption.

Large tunable FMR frequency shift by magnetoelectric coupling in oblique-sputtered Fe52.5Co22.5B25.0/PZN-PT multiferroic heterostructure

In this study, we observe a strong inverse magnetoelectric coupling in Fe52.5Co22.5B25.0/PZN-PT multiferroic heterostructure, which produces large electric field（E-field） tunability of microwave magnetic properties. With the increase of the E-field from 0 to 8 kV/cm, the magnetic anisotropy field Heffis dramatically enhanced from 169 to 600 Oe, which further leads to a significant enhancement of ferromagnetic resonance frequency from 4.57 to 8.73 GHz under zero bias magnetic field, and a simultaneous decrease of the damping constant α from 0.021 to 0.0186. These features demonstrate that this multiferroic composite is a promising candidate for fabricating E-field tunable microwave components.

Al-doping-induced magnetocapacitance in the multiferroic AgCrS_2

In this paper, multiferroics and magnetocapacitive effect of triangular-lattice antiferromagnet Ag Al0.02Cr0.98S2 are investigated by magnetic, ferroelectric, pyroelectric current and dielectric measurement. We find that it is a multiferroic material and the magnetocapacitive effect reaches a factor of up to 90 in an external field of 7 T. The results imply the further possibility of synthesizing the magnetocapacitive materials by modifying the frustrated spin structure in terms of a few B-site doping nonmagnetic ions.

Multiferroic and enhanced microwave absorption induced by complex oxide interfaces

NiFe204 （NFO）/ZnO composite nanoparticles with different ZnO components were investigated, which were pre- pared by a simple wet chemical route method. The magnetoelectric coupling between magnetostriction from NFO and piezoelectricity from ZnO was induced by the surface coating NFO nanoparticles of ZnO layer, NFO/ZnO composite showed ferroelectric properties and the remanent electric polarization reached 0.08 μC/cm. Moreover, the changes of resistance at different room temperatures reached about 2% under 3 T magnetic fields comparing with that of zero mag- netic fields. Furthermore, multiferroic NFO/ZnO resulted in enhancement of microwave absorption due to magnetoelectric coupling.

Al-doping-induced magnetocapacitance in the multiferroic CuCrS_2

In this paper,magnetic and dielectric properties of the quasi-two-dimensional triangular-lattice system CuCrS2 and its B-site-diluted analogs CuAl1-xCrxS2（x = 0.01 and x = 0.02） are investigated.Antiferromagnetic phase transition is observed at about 38.5 K by magnetization measurement without shift induced by a small amount of doping Al.Magnetodielectric effect is found near TN in each of the three compounds.The dielectric constant decreases and the magnetocapacitance increases with the increase of substitution of nonmagnetic Al3＋ ions for the magnetic Cr^3＋ ions.The negative magnetocapacitive effect reaches ～ 13% for CuAl0.02Cr0.98S2.

Electrical control of magnetism in oxides

Recent progress in the electrical control of magnetism in oxides,with profound physics and enormous potential applications,is reviewed and illustrated.In the first part,we provide a comprehensive summary of the electrical control of magnetism in the classic multiferroic heterostructures and clarify the various mechanisms lying behind them.The second part focuses on the novel technique of electric double layer gating for driving a significant electronic phase transition in magnetic oxides by a small voltage.In the third part,electric field applied on ordinary dielectric oxide is used to control the magnetic phenomenon originating from charge transfer and orbital reconstruction at the interface between dissimilar correlated oxides.At the end,we analyze the challenges in electrical control of magnetism in oxides,both the mechanisms and practical applications,which will inspire more in-depth research and advance the development in this field.

Voltage control magnetism and ferromagnetic resonance in an Fe_(19)Ni_(81)/PMN-PT heterostructure by strain

Voltage control magnetism has been widely studied due to its potential applications in the next generation of information technology.PMN-PT,as a single crystal ferroelectric substrate,has been widely used in the study of voltage control magnetism because of its excellent piezoelectric properties.However,most of the research based on PMN-PT only studies the influence of a single tensile(or compressive)stress on the magnetic properties due to the asymmetry of strain.In this work,we show the effect of different strains on the magnetic anisotropy of an Fe_(19)Ni_(81)/(011)PMN-PT heterojunction.More importantly,the(011)cut PMN-PT generates non-volatile strain,which provides an advantage when investigating the voltage manipulation of RF/microwave magnetic devices.As a result,a ferromagnetic resonance field tunability of 70 Oe is induced in our sample by the non-volatile strain.Our results provide new possibilities for novel voltage adjustable RF/microwave magnetic devices and spintronic devices.

Voltage control of ferromagnetic resonance and spin waves

The voltage control of magnetism has attracted intensive attention owing to the abundant physical phenomena associated with magnetoelectric coupling. More importantly, the techniques to electrically manipulate spin dynamics, such as magnetic anisotropy and ferromagnetic resonance, are of great significance because of their potential applications in high-density memory devices, microwave signal processors, and magnetic sensors. Recently, voltage control of spin waves has also been demonstrated in several multiferroic heterostructures. This development provides new platforms for energyefficient, tunable magnonic devices. In this review, we focus on the most recent advances in voltage control of ferromagnetic resonance and spin waves in magnetoelectric materials and discuss the physical mechanisms and prospects for practical device applications.

Coupling-induced ferromagnetic transitions in ferroelectromagnets of weak antiferromagnetic order

A Monte-Carlo simulation on phase transitions in ferroelectromagnets (FEMs) in which a weak antiferromagnetic ordering occurs at the Neel point TN far below the ferroelectric ordering point TE was performed. It is revealed that an intrinsic coupling between spins and electric-dipoles (mp-coupling) does result in a weak ferromagnetic transition from the paramagnetic state at a temperature far above TN, as long as the coupling is strong enough. The magnetoelectric properties as a function of temperature, mp-coupling strength and external electric and magnetic fields were investigated. A mean-field calculation based on the Heisenberg model was performed and a rough consistency between the simulated and calculated ferromagnetic transitions was shown.

Solar manipulations of perpendicular magnetic anisotropy for flexible spintronics

Flexible electronics/spintronics attracts researchers’attention for their application potential abroad in wearable devices,healthcare,and other areas.Those devices’performance(speed,energy consumption)is highly dependent on manipulating information bits(spin-orientation in flexible spintronics).In this work,we established an organic photovoltaic(OPV)/ZnO/Pt/Co/Pt heterostructure on flexible PET substrates with perpendicular magnetic anisotropy(PMA).Under sunlight illumination,the photoelectrons generated from the OPV layer transfer into the PMA heterostructure,then they reduce the PMA strength by enhancing the interfacial Rashba field accordingly.The coercive field(Hc)reduces from 800 Oe to 500 Oe at its maximum,and the magnetization can be switched up and down reversibly.The stability of sunlight control of magnetization reversal under various bending conditions is also tested for flexible spintronic applications.Lastly,the voltage output of sunlight-driven PMA is achieved in our prototype device,exhibiting an excellent angular dependence and opening a door towards solar-driven flexible spintronics with much lower energy consumption.

Multiferroic and in-plane magnetoelectric coupling properties of BiFeO_3 nano-films with substitution of rare earth ions La^(3+) and Nd^(3+)

Single-phase multiferroic BiFeO3 and Bi（0.9）（La/Nd）（0.1）FeO3（doped with rare earth ions La-（3＋） and Nd-（3＋）） films grown on（111）-Pt/Ti/SiO2/Si substrate were prepared via sol-gel method and a subsequent rapid thermal process. The phase composition, microstructure, ferroelectric, dielectric, ferromagnetic properties were investigated, and meanwhile, the in-plane magnetoelectric（ME） coupling effects of the films were reported and studied for the first time in this work. Structural characterization by X-ray diffraction and scanning electron microscopy showed that both BiFeO3 and Bi（0.9）（La/Nd）（0.1）FeO3 exhabited a rhombohedral structure with（111） preferred orientation. The results of the physical properties indicated that the introduction of rare earth ions improved significantly the polarization, magnetization and dielectric properties than the undoped BiFeO3 crystals, and it enhanced effectively the in-plane ME coupling（the ME coupling coefficient αE increased from 0.13 in the pure BiFeO3 to 0.21 in Bi（0.9）La（0.1）FeO3 and 0.34 V/（Oe·cm） in Bi（0.9）Nd（0.1）FeO3）. The mechanism of these phenomena was investigated systematically.

Strain-induced robust magnetic anisotropy and room temperature magnetoelectric coupling effect in epitaxial SmFeO3 film

Rare-earth orthoferrite SmFeO3 is an outstanding single-phase multiferroic material,holding great potential in novel low-power electronic devices.Nevertheless,simultaneous magnetic and ferroelectric orders as well as magnetoelectric(ME)coupling effect at room temperature(RT)in this system have not been demonstrated yet.In this study,epitaxial SmFeO3 films were successfully prepared onto tensile-strain Nb-SrTiO3(Nb-STO)substrates by a pulsed laser deposition(PLD)method.Measurement results show that the films exhibit obvious ferromagnetic and ferroelectric orders at RT.Meanwhile,the magnetic anisotropy gradually changes from out-of-plane(OP)to in-plane(IP)direction with increasing film thickness,which is attributed to the variations of O 2p-Fe 3d hybridization intensity and Fe 3d-orbit occupancy caused by the strain-relaxed effect.Moreover,electrically driven reversible magnetic switching further proves that the SmFeO3 films exhibit the RT ME coupling effect,suggesting promising applications in new-generation electric-write magnetic-read data storage devices.

Effect of Interface Area on Nonlinear Magnetoelectric Resonance Response of Layered Multiferroic Composite Ring

Multiferroic composite structures are widely used in sensing,driving and communication.The study of their magnetoelectric(ME)behavior under various excitations is crucial.This study investigates the nonlinear ME influence of a multilayer composite ring structure consisting of Terfenol-D(TD)magnetostrictive and lead zirconate titanate(PZT)piezoelectric rings utilizing a multiphysics field modeling framework based on the fully coupled finite element method.The ME coupling coefficient of the PZT/TD concentric composite ring is predicted using the linear piezoelectric constitutive model and the nonlinear magnetostrictive constitutive model,which is congruent to the experimental data.The effect of the interface area of a trilayered structure on the coupling performance at the resonant frequency is investigated,considering the magnitude and frequency of the magnetic field and keeping the material ratio constant.The ME coupling coefficient of a trilayered structure is larger than that of a bilayered structure with the same material ratio,and the maximum ME coupling coefficient of a trilayered structure increases nonlinearly with the increase in the interface area.At the resonant frequency,the structure's ME coupling performance is considerably improved.An optimization technique based on structural geometric design and magnetic field control is presented to optimize the ME coupling coefficient.

Enhancing the magnetoelectric coupling of Co4Nb2O9[100] by substituting Mg for Co

We report experimental studies on enhancing the magnetoelectric （ME） coupling of Co4Nb2O9 by sub- stituting the non-magnetic metal Mg for Co. A series of single crystal Co4-xMgxNb2O9 （x = 0, 1, 2, 3） with a single-phase corundum-type structure are synthesized using the optical floating zone method, and the good quality and crystallographic orientations of the synthesized samples are confirmed by the Laue spots and sharp XRD peaks. Although the Neel temperatures （TN） of the Mg substituted crystals decrease slightly from 27 K for pure C04Nb2O9 to 19 K and 11 K for Co3MgNb2O9 and Co2Mg2Nb2O9, respectively, the ME coupling is doubly enhanced by Mg substitution when x = 1. The ME coefficient OlMg of Co3MgNb2O9 required for the magnetic field （electric field） control of electric polarization （magnetization） is measured to be 12.8 ps/m （13.7 ps/m）. These results indicate that the Mg substituted Co4-xMgxNb2O9 （x = 1） could serve as a potential candidate material for applications in future logic spintronics and logic devices.

Recent development of E-field control of interfacial magnetism in multiferroic heterostructures

The full E-field control of multiferroic interfacial magnetism is a long-standing challenge for micro-electromechanical systems(MEMS)and has the potential to transform electronics operation mechanisms.When scaling down conventional complementary metal-oxide semiconductor(CMOS)devices,increased heating dissipation becomes a top concern.Combining the highly correlated ferroic orders,notably the strongly coupled interfacial magnetoelectric(ME)interactions,may lead to devices beyond CMOS.These devices use the electric field to regulate magnetization,which opens up the prospect of downsizing,improved performance,and lower power consumption.To broadly survey this tremendous scope within the last five years,this review summarizes advances in voltage control of interfacial magnetism(VCIM)with various material system selection;controlling effects with different gating methods are also explored.Five classic mechanisms are demonstrated:strain,exchange bias,orbital reconstruction,and the electrostatic and electrochemical.The encouraging photovoltaic approach is also discussed.Each method’s capabilities and application scenarios are compared.Analyses of the comprehensive gating results of different magnetic coupling effects such as perpendicular magnetic anisotropy(PMA)and Ruderman-Kittel-Kasuya-Yosida(RKKY)are additionally made.At last,controlling of skyrmions and two-dimensional(2D)material magnetization is summarized,indicating that E-field gating offers a universal approach with few limitations for material selection.These results point to potential for E-field control interfacial magnetism and predict significant future advancements for spintronics.

A review on all-perovskite multiferroic tunnel junctions

Although the basic concept was proposed only about 10 years ago,multiferroic tunnel junctions(MFTJs)with a ferroelectric barrier sandwiched between two ferromagnetic electrodes have already drawn considerable interests,driven mainly by its potential applications in multi-level memories and electric field controlled spintronics.The purpose of this article is to review the recent progress of all-perovskite MFTJs.Starting from the key functional properties of the tunneling magnetoresistance,tunneling electroresistance,and tunneling electromagnetoresistance effects,we discuss the main origins of the tunneling electroresistance effect,recent progress in achieving multilevel resistance states in a single device,and the electrical control of spin polarization and transport through the ferroelectric polarization reversal of the tunneling barrier.

Multiferroic tunnel junctions

Magnetic tunnel junctions with ferroelectric barriers, often referred to as multiferroic tunnel junc- tions, have been proposed recently to display new functionalities and new device concepts. One of the notable predictions is that the combination of two charge polarizing states and the parallel and antiparallel magnetic states could make it a four resistance state device. We have recently studied the ferroelectric tunneling using a scanning probe technique and multiferroic tunnel junctions using ferromagnetic Lao.7Cao.3MnO3 and Lao.TSro.3MnO3 as the electrodes and ferroelectric （Ba, Sr）TiO3 as the barrier in trilayer planner junctions. We show that very thin （Ba, Sr）TiO3 films can sustain ferroelectricity up till room temperature. The multiferroic tunnel junctions show four resistance states as predicted and can operate at room temperatures.