Magnetoelectric Memory Research Articles

Settlement stability, electrical properties, and magnetoelectric properties of Mn0.5Zn0.5Fe2O4-PbZr0.5Ti0.5O3 multiferroic fluids modulating by particle sizes

Mn0.5Zn0.5Fe2O4-PbZr0.5Ti0.5O3 (MZFO-PZT) multiferroic fluids with different MZFO particle sizes were prepared, and magnetoelectric coupling effects were observed to be enhanced at room temperature. The X-ray diffraction analysis (XRD) indicates that the MZFO and PZT particles are in the pure phases. Scanning electron microscopy (SEM) images illustrate a decrease in MZFO particle size with increased ball milling time. As the MZFO particle sizes decrease, the settlement stability of multiferroic fluids becomes worse. The dielectric constant displays a nonlinear variation, exhibiting a maximum value of 4.52 at 140 Hz when the MZFO particle size is 0.55 μm. The residual polarization strength decreases and increases as particle size decreases, while the saturation polarization strength decreases gradually. The application of magnetic field results in a notable enhancement of the dielectric characteristics and ferroelectric properties, which indicates the presence of magnetodielectric and magnetoelectric coupling effects. The magnetoelectric coupling coefficient (αME) is 15.14 V/(cm·Oe) when the MZFO particle size is 0.61 μm. By modifying the strength of the applied magnetic field, the αME attains a maximum value of 114.43 V/(cm·Oe). This approach offers an effective strategy for optimizing the magnetoelectric coupling effect of multiferroic materials. Therefore, it is expected to be used in new magnetoelectric devices such as magnetoelectric random memories and magnetic field sensors.

Evidence of self-biased magnetoelectric coupling in eco-friendly (Na0.41K0.09Bi0.5TiO3-Ba0.85Ca0.15Zr0.1Ti0.9O3)-(CoFe2O4) particulate composites

The magnetoelectric (ME) properties of eco-friendly 1-x(0.94Na0.41K0.09Bi0.5TiO3-0.06Ba0.85Ca0.15Zr0.1Ti0.9O3)-x (CoFe2O4) (NKBCZT-CFO) with x = 0, 0.1, 0.2, 0.3 and 0.4 particulate composites were investigated. The X-ray diffraction studies provided evidence for the simultaneous existence of constituent phases (ferroelectric and ferromagnetic) in the composite. The structural and surface morphology analysis of the composite affirmed the homogeneous and densely packed distribution of CFO grains within the NKBCZT matrix. The composite's multiferroic behavior at room temperature was confirmed through the characterization of P vs E and M vs H hysteresis loops. The observed values of remnant polarization (Pr) and coercive field (Ec) are 26.7 μC/cm2 and 35.5 kV/cm, respectively, for 10 mol% of CFO. The increase in CFO content resulted in a decrease in the ferroelectric properties, possibly due to the conductive behaviour exhibited by CFO, and correlated with leakage current measurement. For the composite containing 40 mol% of CFO, the estimated values of remanent (Mr), saturation (Ms) magnetization, coercive field (Hc), and magnetic moment (µB) are 2.35 emu/g, 21.85 emu/g, 104.2 Oe, and 0.86 µB, respectively. The non-Debye type dielectric relaxation processes have been observed in the composites, and the electron hopping mechanism resulted in a higher dielectric constant (εʹ). Enhancement in relaxor nature had been observed through Vogel-Fulcher analysis with CFO content. The evidence of ME coupling was revealed through the direct ME voltage coefficient (αME) and magnetocapacitance (MC) measurement. The observed maximum value of MC measured at 1 kHz for the 20 mol% CFO is ∼5.6 %. Self-biased ME coupling (non-zero αME at HDC = 0 Oe) was observed in 20 and 30 mol% of CFO composite. The highest measured value of αME for 20 and 30 mol% CFO is 3.63 mV/cm.Oe and 4.09 mV/cm.Oe at HDC = 0 Oe respectively. The strong ME interaction and significant value of self-biased ME αME suggest that these composites can be explored for magnetic sensor and ME memory device applications.

A high-performance magnetoelectric non-volatile light-emitting memory device

A novel magnetoelectric light-emitting memory (LEM) device that can control the output light intensity and electrical signal based on the input magnetic and electric field strengths has been proposed and demonstrated.

Modulating the ferromagnetism of Fe3GeTe2 with 3d transition metal adsorption and strain-engineering

Two-dimensional ferromagnetic materials hold great promise to develop energy-efficient magnetoelectric memory devices and next-generation spintronics. However, one of the crucial challenges for these materials is the realization of tunable magnetocrystalline anisotropy (MCA) to balance thermal stability and energy efficiency. Here, we systematically study the adsorption effects of 3d transition metals (3d-TMs) on the electronic structure and magnetic property of the Fe3GeTe2 (FGT) monolayer. The adsorption systems exhibit different ground state configurations depending on the adatoms, while the controlled perpendicular magnetic anisotropy has also been achieved. Notably, the Mn/FGT system can maintain the out-of-plane magnetic orientation with a changing amplitude of MCA energy up to 3.057 erg/cm2 as the external strain varies from −4% to 1%. In contrast, the Fe/FGT structure undergoes spin reorientation from in-plane to out-of-plan magnetization with a distinct modification behavior of MCA. We elucidate that the underlying atomistic mechanism mainly arises from the alteration of Fe-derived 3d-orbital states in response to the strain effect, leading to competitive changes in the different coupling states. These findings can not only provide useful guidance to optimize two-dimensional magnets for fundamental research but also reveal the promising potential of TMs/FGT materials for the development of ultra-low energy spintronic devices.

Analysis of the microstructural and magnetodielectric behavior in multiferrioc Cr1.3Fe0.7O3 nanoparticles

Single phase Cr1.3Fe0.7O3 has been successfully prepared by wet chemical method, accompanied by the surface morphology with pure diamond shaped structure of corundum and uniform grain growth. The splitting of magnetization curves at ∼220 K during varying temperature measurement indicates the magnetocrystalline anisotropy with the coexistence of antiferromagnetic and ferromagnetic phases. The obvious dielectric relaxation behavior has been determined above ∼125 K with the activation energy of 0.0318 eV, which is attributed to the dipolar relaxation caused by short-range polaron range hopping in the magnetic grains. The arresting magnetoelectric coupling effect near room temperature is certified in Cr1.3Fe0.7O3 from ∼125 K, with the maximum coupling coefficient of 5 % at ∼212 K. These characteristics mean that the sample has potential application value in fields such as spintronics devices and magnetoelectric memories.

Electric field-controlled deterministic magnetization reversal in nanomagnet Fe3Si/PMN-PT multiferroic heterostructures

Pure electric field-controlled 180° magnetization switching plays a vital role in low-power magnetoelectric memory devices. Using micromagnetic simulation, we engineered a square-shaped epitaxial Fe3Si nanomagnet on a PMN-PT piezoelectric substrate to make the magnetic easy axis slightly deviate 18° from the piezostrain axis, aiming to break the symmetry of the magnetization distribution and achieve deterministic magnetization reversal paths. Under the coaction of a magnetic field and an electric field, the simulated magnetic hysteresis loops and magnetic domain patterns reveal a fourfold to twofold magnetic anisotropy transition and magnetization reversal paths. Stimulated by pure electric field-induced piezoelectric strain, deterministic 180° magnetization reversals are accomplished by the two successive clockwise 90° switching process. The results help to comprehend electrically regulated deterministic magnetization reversal and pave an avenue for designing multistate spintronics devices.

Voltage-controlled magnetic double-skyrmion states in magnetoelectric elliptical nanostructures by phase-field model

The magnetic skyrmions are promising candidates as information carriers for future energy-efficient spintronic devices (e.g. memory, sensor, logic). Moreover, manipulating elliptically distorted skyrmions can result in a variety of novel functions that differ from those of conventional circular skyrmions. Despite the tremendous prospects, achieving voltage-driven dynamics of the elliptically distorted skyrmions remains a key challenge. Here, we employ dynamical phase-field simulations that consider the strain-mediated magnetoelectric coupling to demonstrate electric field manipulates the dynamic behavior of the elliptically distorted skyrmions. This study finds that the elliptically distorted skyrmions can split into smaller-sized circular skyrmions and reversibly switch between the single domain - single skyrmion and single domain - double skyrmion on elliptical nano-islands. The stabilization of magnetic skyrmions and double skyrmions in multiferroic heterostructures essentially depends on the ratio of the major axis and the minor axis of the elliptical nono-islands. Intriguingly, the operation is non-volatile and exhibits a multistate character. The temporal behavior of energy density variations during the evolution of magnetic domain structures indicates that the electric-field manipulation of skyrmions originates from the competition between elastic, demagnetization, and anisotropic energies. Our work shows that deterministic switching of multiple domain structures on elliptical nano-islands is achievable, indicating the morphology is a new degree of freedom for manipulating the voltage-driven dynamics of skyrmions, providing a novel avenue to develop magnetoelectric coupling-based memory devices, logic devices, sensor devices, etc., at the nanoscale. Impact statementThis research aims to construct a unique multi-state storage device as well as to indicate the morphology is a new degree of freedom for manipulating the voltage-driven dynamics of skyrmions, giving a fresh way to create nanoscale magnetoelectric coupling-based memory, logic, sensor, and other devices.

Electric‐Field‐Tunable Bipolar Linear Magnetoelectric Effect in Zigzag Graphene Nanoribbon‐Based Antiferromagnet

Modern electronic devices are moving toward miniaturization and integration. Therefore, achieving electrical control of magnetization effectively in 1D materials represents a promising field for the practical applications in memory elements. Herein, it is discovered, from first‐principles calculations, that an electric‐field‐tunable bipolar linear magnetoelectric effect can be realized in 1D antiferromagnets based on double‐Gd‐adsorbed graphene nanoribbon with four zigzag carbon chains (2Gd‐4ZGNR). It is found that, compared with the bare 4ZGNR, the adsorption of two Gd atoms on the 4ZGNR reduces the bandgap. As a result, 2Gd‐4ZGNR transits from antiferromagnetic semiconductor to ferrimagnetic metal at a relatively low critical external transverse (perpendicular) electric field, where the net magnetic moment can be induced. The antiferromagnetism and inversion‐symmetrical crystal structure further allow to realize a bipolar linear magnetoelectric effect, where the 2Gd‐4ZGNR forms two groups of independent linear magnetic response states, acting as a magnetoelectric memory element.

Electrically-Excited Motion of Topological Defects in Multiferroic Materials

Topological magnetic defects in multiferroic materials acquire an electric charge or dipole moment due to the inverse Dzyaloshinskii-Moriya mechanism. This magnetoelectric coupling makes possible to excite large-amplitude collective motion of topological magnetic textures with an oscillating electric field. Here, I discuss electric excitation of a polar optical mode in a vortex-antivortex crystal and the electrically-induced spin precession in a magnetic skyrmion, which gives rise to rotation of skyrmions around each other and a translational motion of skyrmion-antiskyrmion pairs. The electric manipulation of magnetic topological defects in Mott insulators can find applications in magnetoelectric memory and logical devices.

Magnetoelectricity Enhanced by Electron Redistribution in a Spin Crossover [FeCo] Complex.

Molecular-based magnetoelectric materials are among the most promising materials for next-generation magnetoelectric memory devices. However, practical application of existing molecular systems has proven difficult largely because the polarization change is far lower than the practical threshold of the ME memory devices. Herein, we successfully obtained an [FeCo] dinuclear complex that exhibits a magnetic field-induced spin crossover process, resulting in a significant polarization change of 0.45 μC cm-2. Mössbauer spectroscopy and theoretical calculations suggest that the asymmetric structural change, coupled with electron redistribution, leads to the observed polarization change. Our approach provides a new strategy toward rationally enhancing the polarization change.

A magnetoelectric memory device based on pseudo-magnetization

We propose a new type of magnetoelectric memory device that stores magnetic easy-axis information or pseudo-magnetization, rather than a definite magnetization direction, in magnetoelectrically coupled heterostructures. Theoretically, we show how a piezoelectric/ferromagnetic (PE/FM) combination can lead to non-volatility in pseudo-magnetization exhibiting overall ferroelectric-like behavior. The pseudo-magnetization can be manipulated by extremely low voltages especially when the FM is a low-barrier nano-magnet. Using a circuit model benchmarked against experiments, we determine the switching energy, delay, switching probability and retention time of the envisioned 1T/1C memory device in terms of magnetic and circuit parameters and discuss its thermal stability in terms of a key parameter called back-voltage vm which is an electrical measure of the strain-induced magnetic field. Taking advantage of ferromagnetic resonance measurements, we experimentally extract values for vm in CoFeB films and circular nano-magnets deposited on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 which agree well with the theoretical values. Our experimental findings indeed indicate the feasibility of the proposed novel device and confirm the assumed parameters in our modeling effort.

The optical and ferroelectric properties of Fe-doped hybrid improper ferroelectricity Ca3Ti2O7 via experimental and density functional theory study

The magnetoelectric multiferroic materials with ferroelectric and magnetic orders have great attributed attention in the field of magnetoelectric memories and magnetic resonance devices. Here, we systematically investigated the optical and multiferroic properties of Fe-doped hybrid improper ferroelectricity Ca3Ti2O7 prepared by sol-gel method. The distortion of TiO6 octahedron changes with the content of oxygen vacancy introduced by Fe doping, thus realizing the adjustment of remnant ferroelectric polarization of the samples. The slight blue shift of the Raman band at 667 cm−1 reflected the introduces of oxygen vacancies by Fe doping. The optical bandgaps of the doped samples were reduced after doping, agreeing with the results of the first-principles calculations. With the introduction of Fe3+, the magnetism increases gradually. The first-principles calculation shows that magnetism origins from the Fe-3d and their surrounding O-2p orbitals. The Fe-doping Ca3Ti2O7 materials realizing the introduction of magnetic properties while regulating its ferroelectric properties are expected to be applied in magnetoelectric memories, optoelectronic devices spintronics and magnetic response devices.

Growth of Samarium-Substituted Epitaxial Bismuth Ferrite Films by Chemical Vapor Deposition

There is great interest in BiFeO3 and various substituted heterostructures for ferroelectric random-access memory (RAM) and energy-efficient magnetoelectric logic and memory devices. High-quality heterostructures of these material systems with smooth topography are desirable to incorporate into functional devices. For this purpose, the direct liquid injection chemical vapor deposition (DLI-CVD) technique has been employed to grow BiFeO3 and Bi-site samarium-substituted epitaxial films on (001)-oriented SrTiO3 and SrRuO3-buffered SrTiO3 substrates. Structural and morphological characterizations of the films are carried out using X-ray diffraction, atomic force microscopy, and scanning electron microscopy techniques. The films show textured growth and exhibit smooth morphology with root mean square roughness below 2.5 nm. Ferroelectric characteristics and memory retention in thin films are demonstrated using piezoresponse force microscopy. The thickness scaling of the switching voltage has been analyzed to validate the Kay–Dunn law for Sm-substituted BiFeO3 and compared with that of pure BiFeO3.

Magnetoelectric memory cell based on 0.5Ba(Zr0.2Ti0.8)O3-0.5Ba0.7Ca0·3TiO3/Fe65Co35 thin films

In this study, 0.5Ba(Zr0·2Ti0.8)O3-0.5Ba0·7Ca0·3TiO3(0.5BZT-0.5BCT) thin films were deposited on Pt/Ti/SiO2/Si substrate, and then small area Fe65Co35(FeCo) films were deposited on 0.5BZT-0.5BCT films. The hysteresis loops and piezoelectric curves of 0.5BZT-0.5BCT films were studied. The results show that the piezoelectric displacement of 0.5BZT-0.5BCT films is 63 Å, the residual polarization intensity is 2.76 μC/cm2 and the coercive field is 110 kV/cm. 0.5BZT-0.5BCT/FeCo composite films exhibit typical magnetic hysteresis loops and stripe-like domains, the in-plane and out-of-plane coercivities are 10 Oe and 94 Oe, respectively, which indicates that the thin films have good soft magnetic properties. The current-voltage (I–V) curves of FeCo films on 0.5BZT-0.5BCT films were studied, the I–V behaviors of the thin films could be modulated by applying bias voltage, resulting in a resistance switching behavior. The maximum resistance change is 94% at 10 V bias voltage and 1 V scan voltage.

Selective Dual-Ion Modulation in Solid-State Magnetoelectric Heterojunctions for In-Memory Encryption.

Nanoionic technologies are identified as a promising approach to modulating the physical properties of solid-state dielectrics, which have resulted in various emergent nanodevices, such as nanoionic resistive switching devices and magnetoionic devices for memory and computing applications. Previous studies are limited to single-type ion manipulation, and the investigation of multiple-type ion modulation on the coupled magnetoelectric effects, for developing information devices with multiple integrated functionalities, remains elusive. Here, a dual-ion solid-state magnetoelectric heterojunction based on Pt/HfO2- x /NiOy /Ni with reconfigurable magnetoresistance (MR) characteristics is reported for in-memory encryption. It is shown that the oxygen anions and nickel cations can be selectively driven by voltages with controlled polarity and intensity, which concurrently change the overall electrical resistance and the interfacial magnetic coupling, thus significantly modulate the MR symmetry. Based on this device, a magnetoelectric memory prototype array with in-memory encryption functionality is designed for the secure storage of image and digit information. Along with the advantages including simple structure, multistate encryption, good reversibility, and nonvolatile modulation capability, this proof-of-concept device opens new avenues toward next-generation compact electronics with integrated information functionalities.

Linear magnetoelectric memory and training effect in the honeycomb antiferromagnet Co4Nb2O9

We report observation of ultrarobust linear magnetoelectric memory and significant training effect in a honeycomb antiferromagnet ${\mathrm{Co}}_{4}{\mathrm{Nb}}_{2}{\mathrm{O}}_{9}$, which is controllable by magnetic and electric fields. The memory states show distinct linear magnetoelectric coefficients over a broad magnetic field range. Antiferromagnetic domain evolution is believed to be responsible for the versatile memory behaviors promisingly accessible in multiferroics and other magnetoelectric materials such as topological insulators. The compensated antiferromagnetic phase essential to the magnetoelectric memory may allow to further integrate the unique merits of antiferromagnetic spintronics such as ultrahigh density and ultrafast switching.

Enhanced magnetism in Ru‐doped hybrid improper perovskite Ca3Mn2O7 via experimental and first‐principles study

AbstractThe quasi‐2D Ruddlesden–Popper layered perovskites with single‐phase multiferroicity have attracted much attention in recent magnetoelectric memory applications. We have systematically investigated the optical and magnetic properties of Ru‐doped hybrid improper perovskite Ca3Mn2O7 both experimentally and using first‐principles calculations. The Ca3RuxMn2−xO7 (x = 0, 0.02, 0.06, 0.10) powders were successfully synthesized using the sol–gel method. Ru doping enhanced the ferromagnetism of Ca3Mn2O7. The quasi‐2D antiferromagnetic (AFM) fluctuation effect was observed in Ca3Mn2O7 and in certain doped samples. We also found that the optical bandgaps of the doped samples were reduced after doping, agreeing with the results of the first‐principles calculations. Infrared absorption spectra indicated the distortion of the Mn–O bonds was possibly due to the Jahn–Teller effect. To analyze the electronic structures and to understand the detailed atomic contributions of magnetic moments, the Crystal Orbital Hamilton Population (COHP) and Integrated COHP of the (Mn,Ru)O6 octahedra were also calculated. The Ru‐doped materials with the coexistence of ferromagnetic and AFM orderings are expected to be excellent candidates for magnetoelectric devices.

Hexagonal Lu1-xInxFeO3 Room-Temperature Multiferroic Thin Films.

The hexagonal rare earth ferrites h-RFeO3(R = rare earth element) have been recognized as promising candidates for a room-temperature multiferroic system, and the primary issue for these materials is how to get a stable hexagonal structure since the centrosymmetric orthorhombic structure is generally stable for most RFeO3 at room-temperature, while the hexagonal phase is only stable under some strict conditions. In the present work, h-Lu1-xInxFeO3 (x = 0-1) thin films were prepared on a Nb-SrTiO3 (111) single-crystal substrate by a pulsed laser deposition (PLD) process, and the multiferroic characterization was performed at room temperature. With the combined effects of chemical pressure and epitaxial strain, the stable hexagonal structure was achieved in a wide composition range (x = 0.5-0.7), and the results of XRD (X-ray diffraction) and SAED (selected area electron diffraction) indicate the super-cell match relations between the h-Lu0.3In0.7FeO3 thin film and substrate. The saturated P-E hysteresis loop was obtained at room temperature with a remanent polarization of about 4.3 μC/cm2, and polarization switching was also confirmed by PFM measurement. Furthermore, a strong magnetoelectric coupling with a linear magnetoelectric coefficient of 1.9 V/cm Oe was determined, which was about three orders of magnitude larger than that of h-RFeO3 ceramics. The present results indicate that the h-Lu1-xInxFeO3 thin films are expected to have great application potential for magnetoelectric memory and detection devices.

Enhanced Stability of the Multiferroic Phase in Cr-Doped Y -Type Hexaferrite Single Crystals

The material family of $Y$-type hexaferrites is among the most promising candidates for magnetoelectric memory applications. The magnetoelectric properties in this class of magnets are dominated by a multiferroic phase, termed the FE3 phase, where spin-driven polarization can be switched by a magnetic field, and, conversely, a full magnetic moment can be reversed by an electric field. In this study, we discuss the effect of Cr doping on the stability of competing magnetic and multiferroic phases in the $Y$-type hexaferrites ${\mathrm{Ba}\mathrm{Sr}\mathrm{Co}}_{2}{\mathrm{Fe}}_{12\ensuremath{-}x\ensuremath{-}\ensuremath{\delta}}{\mathrm{Al}}_{x}{\mathrm{Cr}}_{\ensuremath{\delta}}{\mathrm{O}}_{22}$ with $x=0.9$ and $\ensuremath{\delta}=0.00$, 0.05, and 0.10. We find that Cr doping increases the stability of the multiferroic FE3 phase; while in the Cr-free compound the alternating longitudinal conical (ALC) and proper screw phases are stabilized as zero-field-cooled magnetic phases, the FE3 phase appears besides the ALC phase as a stable zero-field-cooled phase in the $\ensuremath{\delta}=0.05$ and 0.10 compounds. Moreover, a spin-induced large polarization is observed at and above room temperatures with antisymmetric magnetic field dependence. The magnetoelectric properties, in particular the coupling between polarization and magnetization, are investigated via the measurements in the simultaneous presence of electric and magnetic fields. We find the enhanced stability of the magnetoelectic responses from the multiferroic FE3 phase upon Cr doping, while the coupling between the polarization and magnetization is preserved.

Ultra-Sensitive Magnetoelectric Sensors of Magnetic Fields for Biomedical Applications

Composite multiferroics are materials in which electric polarization of the material is possible under the action of an external magnetic field and vice versa, a change in the magnetization of the structure when an electric field is applied. Such properties have a high practical potential for application in science and technology. Based on these materials, it is possible to manufacture a number of devices with unique properties, such as, for example, random access magnetoelectric (ME) memory, ME sensors of magnetic fields, current, magnetic nanoparticles, micromechanical ME antennas, voltage-adjustable microwave filters, resonators and phase shifters. Therefore, the search for new materials of composite multiferroics and the study of the ME effect in them is a priority and urgent task in the search and creation of new electronic devices. One of the most promising and close to practical implementation directions is the creation of highly sensitive sensors of ultra-weak magnetic fields on the basis of composite multiferroics. The absence of the need to cool such sensors is a significant technical advantage over superconducting quantum interferometers currently used for these purposes. To date, the best achieved limits for detecting magnetic fields using sensors based on composite magnetoelectrics are values of the order of pT/Hz1/2, and new works are regularly published that reduce this threshold by improving processing electronics and changing the sensor design. This threshold of sensitivity is already sufficient for reliable detection of magnetic fields induced by alpha-rhythm currents of the brain with amplitudes of units of pT (magnetoencephalography) and for detecting the magnetic activity of the human heart. The review article is devoted to composite magnetoelectric structures with a focus on sensor structures capable of detecting ultra-weak magnetic fields. The comparison of the limiting sensitivity to the magnetic field of the existing ME composite structures is carried out, the ways of increasing the sensitivity to the magnetic field are shown.