Large Magnetoelectric Effect Research Articles

Stoner instability-mediated large magnetoelectric effects in 2D stacking electrides

Strong magnetoelectric effects in single-phase two-dimensional (2D) materials are extremely rare in nature. Here by first-principles calculations, we find a strong magnetoelectric coupling in polar stacking bilayer Hf2S that allows the reversal of net magnetic moments with the reversal of electric dipoles. Further analysis shows that such strong magnetoelectric effects benefit from the Stoner instability of surface Hf atoms triggered by polar stacking. Moreover, an unexpectedly large out-of-plane electric polarization (which is at least two times larger than that of bilayer BN) survives in the material, despite its metallicity. The large electric polarization is ascribed to the delocalized interlayer electrons which generally present in layered electride materials. It is quite interesting that large electric polarization, metallicity and magnetism coexist in one single-phase material. Our findings reveal rich physical phenomena to be explored in 2D stacking multiferroics and suggest an alternative way of searching for strong magnetoelectric materials with ultrathin thickness.

Magnetoelectric effects in ferromagnetic metal monolayers

Manipulating magnetic properties by purely electrical means is a key challenge to improve information technology. In the three-dimensional ferromagnetic (FM) metal thin films, for example, the 3d-transitonal metal thin films Fe, Co, and Ni, the electric-field effect is restricted within the surface around 2–3 Å due to the screening effect, and it is hard to separate the bulk and surface states. In the present investigation, through first-principles calculations, we explore the electric-field effect on the two-dimensional (2D) FM metal monolayers Fe3GeTe2, Fe3GeSe2, and Fe3GeTeSe. It is found that magnetic anisotropy energy (MAE) of these three materials follows the sequence: Fe3GeTe2 > Fe3GeTeSe > Fe3GeSe2, because the atomic spin–orbital coupling of Te is much stronger than that of Se. The most interesting finding is that the electric-field effect on MAE is obviously enhanced in Fe3GeTeSe, which is nearly ten times of Fe3GeTe2 and Fe3GeSe2, and we find the large difference results from its asymmetric structure. Our investigation reveals the magnetoelectric (ME) mechanism and obtains the large ME effect, which is of great significance in the 2D magnetoelectronics.

Phase Transitions in Magneto-Electric Hexaferrites.

Hexaferrites have long been the object of extensive studies because of their great possibility for applications-permanent magnets, high-density recording media, microwave devices, in biomedicine, to name but a few. Lately, many researchers' efforts have been focused on the existence of the magneto-electric effect in some hexaferrite systems and the appealing possibility of them being used as single-phase multiferroic and magneto-electric materials. As indicated by theoretical analyses, the origin of the large magneto-electric effect can be sought in the strong interaction between the magnetization and the electric polarization that coexist in insulators with noncollinear magnetic structures. The hexaferrites' magnetic structure and, particularly, the specific magnetic spin ordering are the key factors in observing magneto-electric phases in hexaferrites. Some of these phases are metastable, which hampers their direct practical use. However, as the hexaferrites' phase diagrams reveal, chemical doping can be used to prepare a number of noncollinear stable magnetic phases. Since the magneto-electric effect has to do with the magnetic moments ordering, it seems only logical that one should study the cation substitutions' influence on the magnetic phase transition temperature. In this paper, we summarize recent examples of advances in the exploration of magnetic phase transitions in Y-type hexaferrites. In particular, the effect is emphasized by substituting in Y-type hexaferrites the nonmagnetic Me2+ cations with magnetic ones and of the magnetic Fe3+ cations with nonmagnetic ones on their magnetic properties and magnetic phase transitions. The work deals with the structural properties of and the magnetic phase transitions in a specific Y-type hexaferrite, namely, Ba(Sr)2Me2Fe12O22.

Lithium‐Ion Battery Technology for Voltage Control of Perpendicular Magnetization

AbstractThe voltage control of magnetism is a promising path to the development of low‐power spintronic devices. Magneto‐ionics—exploiting voltage‐driven ion migration to control magnetism—has attracted interest because it can generate large magnetoelectric effects at low voltage. Here, the use of the solid‐state lithium‐ion battery technology for reversible voltage‐controlled switching between perpendicular and in‐plane magnetization states in a Co–Pt bilayer is demonstrated. Due to the small size and high mobility of lithium ions, small voltages produce an exceptionally high magnetoelectric coupling efficiency of at least 7700 fJ V–1 m–1 at room temperature. The magnetic switching effect is attributed to the modulation of spin‐orbit coupling at the Co–Pt interface when lithium ions migrate between a lithium storage layer (LiCoO2) and the magnetic interface across a lithium phosphorous oxynitride (LiPON) solid‐state electrolyte, which is corroborated by density functional theory calculations. Voltage control of magnetism in the battery structure does not show degradation over more than 500 voltage cycles, demonstrating promise for solid‐state lithium‐based magneto‐ionic devices.

Self-biased Metglas/PVDF/Ni magnetoelectric laminate for AC magnetic sensors with a wide frequency range

In this work, an arc-shaped Metglas/polyvinylidene fluoride (PVDF)/Ni laminate is proposed, which exhibits a large self-biased magnetoelectric (ME) effect due to the internal magnetization gradient field between the two magnetic layers and the built-in stress formed from the arc-shaped structure. The ME coefficients reach 38.24 and 15.0 V cm−1 Oe−1 without a DC bias magnetic field at resonance and nonresonant frequencies, respectively. The sample shows a high sensitivity, resolution and linearity with values of 210.07 mV Oe−1, 1 nT and 0.9999 at the resonance frequency, respectively. The sample was then used to detect AC magnetic fields with different nonresonant frequencies (ranging from 1 to 25 kHz), resulting in the measured data being in good agreement with the actual data. Under a zero bias magnetic field and at frequencies of 40 and 1 Hz, the limit of detection can reach 2 and 8 nT, and the resolution can reach 1 and 4 nT, respectively. The results indicate that the arc-shaped Metglas/PVDF/Ni laminate shows a large self-biased ME effect and good AC magnetic sensing performance in the bending state, which provides a new way to develop a wide frequency range AC magnetic sensor.

Crystal structure of bismuth-containing NdFe3(BO3)4 in the temperature range 20-500 K.

Neodymium iron borate NdFe3(BO3)4 is an intensively studied multiferroic with high electric polarization values controlled by a magnetic field. It is characterized by a large quadratic magnetoelectric effect, rigidity in the base plane and a rather strong piezoelectric effect. In this work, the atomic structure of (Nd0.91Bi0.09)Fe3(BO3)4 was studied by single-crystal X-ray diffraction in the temperature range 20-500 K (space group R32, Z= 3). The Bi atoms found in the composition partially substitute the Nd atoms in the 3a position; they entered the structure due to the growth conditions in the presence of Bi2Mo3O12. It was shown that in the temperature range 20-500 K there is no structural phase transition R32→P3121, which occurs in rare-earth iron borates (RE= Eu-Er, Y) with an effective rare-earth cation radius smaller than that of Nd. The temperature dependence of the unit-cell c parameter reveals a slight increase on cooling below 90 K, which is similar to the results obtained previously for iron borates of Gd, Y and Ho. The atomic distances (Nd,Bi)-O, (Nd,Bi)-B, (Nd,Bi)-Fe, Fe-O, Fe-B and Fe-Fe in the iron chains and between chains decrease steadily with decreasing temperature from 500 to 90 K, whereas the B1(3b)-O distance does not change and the average B2(9e)-O distance increases slightly. There is a uniform decrease in the atomic displacement parameters with decreasing temperature, with a more pronounced decrease for the Nd(3a) and O2(9e) atoms. The O2(9e) atoms are characterized by the maximum atomic displacement parameters and the most elongated atomic displacement ellipsoids. The characteristic Debye and Einstein temperatures, and the static component in the atomic displacements were determined for cations using multi-temperature diffraction data. It was shown that the Nd cations have the weakest bonds with the surrounding atoms and the B cations have the strongest.

Kinetic magnetoelectric effect in topological insulators

The kinetic magnetoelectric effect is an orbital analog of the Edelstein effect and offers an additional degree of freedom to control magnetization via the charge current. Here we theoretically propose a gigantic kinetic magnetoelectric effect in topological insulators and interpret the results in terms of topological surface currents. We construct a theory of the kinetic magnetoelectric effect for a surface Hamiltonian of a topological insulator, and show that it well describes the results by direct numerical calculation. This kinetic magnetoelectric effect depends on the details of the surface, meaning that it cannot be defined as a bulk quantity. We propose that Chern insulators and Z2 topological insulators can be a platform with a large kinetic magnetoelectric effect, compared to metals by 5–8 orders of magnitude, because the current flows only along the surface. We demonstrate the presence of said effect in a topological insulator, identifying Cu2ZnSnSe4 as a potential candidate.

Prediction of magnetoelectric properties of defect BiFeO3 thin films using Monte Carlo simulations

Magnetoelectric materials have received astonishing attention due to their great potential for nanotechnology and magnetoelectric applications. Herein, the ferroelectric, magnetic and magnetoelectric properties of multiferroic BiFeO3 (BFO) thin films have been carried out using Monte Carlo simulation investigations in the framework of the Heisenberg model. Exchange coupling interactions in magnetic and ferroelectric sublattices that correspond to the experimental critical temperature were estimated. Temperature dependence of the internal energy, specific heat, magnetization, electric polarization and their susceptibilities in BFO thin films have been systematically analyzed. Moreover, the effect of magnetoelectric coupling interaction Jme on M−H and P-H hysteresis loopsand magnetoelectric voltage coefficient were studied. A large magnetoelectric voltage coefficient of 104 mV/(cm.Oe) was predicted in BFO thin films with 25% defects. Furthermore, the defect mechanism can be used to control the polarization switching by the magnetic field in BFO system. The obtained results highlight the large magnetoelectric effect in BFO multiferroic thin films for multifunctional magnetoelectric devices.

Poly(vinylidene fluoride-trifluoroethylene)/cobalt ferrite composite films with a self-biased magnetoelectric effect for flexible AC magnetic sensors

With the rapid development of artificial intelligence and wearable devices, flexible magnetic sensors have attracted much attention in recent years. In this work, large self-biased 0–3 type poly(vinylidene fluoride-trifluoroethylene)/cobalt ferrite (P(VDF-TrFE)/CoFe2O4) flexible magnetoelectric (ME) composite films are proposed for the development of AC magnetic sensors. P(VDF-TrFE)/CoFe2O4 composite films with CoFe2O4 nanoparticle mass contents from 5 to 30% are successfully fabricated through the solution casting method. The results show that the nanoparticles are homogeneously dispersed in the P(VDF-TrFE) matrix, and the composite films have both excellent ferroelectric and ferromagnetic properties. The P(VDF-TrFE)/CoFe2O4 composite films all exhibit a large ME effect. The ME coefficient reaches 47.1 mV·cm−1·Oe−1 for the film with a CoFe2O4 nanoparticle mass content of 20% at resonance frequency. Moreover, the composite films have a large self-biased ME effect with a maximum value of 20.4 mV·cm−1·Oe−1, which is mainly due to the high remnant magnetization of CoFe2O4 nanoparticles. To evaluate the composite films for application in magnetic sensors, the response of the ME output voltage to an AC magnetic field without a bias DC magnetic field was measured. The good linear correlation coefficient, sensitivity and repeatability indicate that the proposed 0–3 type P(VDF-TrFE)/CoFe2O4 composite film is a promising material for flexible AC magnetic sensors.

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.

Ferroelectric, ferromagnetic, and magnetoelectric properties of Bi3.15Nd0.85Ti2.9Zr0.1O12–CoFe2O4 composite films with large magnetoelectric coupling effect

The magnetoelectric composite films of Bi3.15Nd0.85Ti2.9Zr0.1O12 (BNTZO)–CoFe2O4 (CFO) were deposited on the substrates of Pt/Ti/SiO2/Si (111) by means of the sol–gel method. The results show that, in the composite films, there are tri-axial compressive stresses in the CFO films. Nevertheless, there are bi-axial tensile stresses and uniaxial compressive stress in the BNTZO films. The composite films possess compact microstructure and flat interface without forming intermediate layer. The composite films have good magnetoelectric properties besides both good ferroelectric and ferromagnetic properties. When Hdc is 738 Oe, the composite film of BNTZO-CFO possesses the maximum of αE, 114 mV cm−1 Oe−1, which is helpful for the application in multi-functional devices.

Ferroelectrically tunable magnetism in BiFeO3/BaTiO3 heterostructure revealed by the first-principles calculations

The perovskite oxide interface has attracted extensive attention as a platform for achieving strong coupling between ferroelectricity and magnetism. In this work, robust control of magnetoelectric (ME) coupling in the BiFeO3/BaTiO3 (BFO/BTO) heterostructure (HS) was revealed by using the first-principles calculation. Switching of the ferroelectric polarization of BTO induce large ME effect with significant changes on the magnetic ordering and easy magnetization axis, making up for the weak ME coupling effect of single-phase multiferroic BFO. In addition, the Dzyaloshinskii-Moriya interaction (DMI) and the exchange coupling constants J for the BFO part of the HSs are simultaneously manipulated by the ferroelectric polarization, especially the DMI at the interface is significantly enhanced, which is three or four times larger than that of the individual BFO bulk. This work paves the way for designing new nanomagnetic devices based on the substantial interfacial ME effect.

Suppression of magnetoelectric effects in DyCrO4 by chemical doping

The scheelite-type DyCrO4 shows a large linear magnetoelectric effect and field-induced ferromagnetism and ferroelectricity. In this article, we investigate the Bi-doping effects on the crystal structure, magnetism, dielectric constant, and electric polarization for a Dy1−xBixCrO4 (x = 0, 0.05, 0.1) solid solution. The substitution of Bi for Dy up to 10% does not change the structure and antiferromagnetic ordering temperature very much. However, it remarkably suppresses the magnetodielectric effect from 14% in the parent phase to 3.2% in the x = 0.1 sample. More sharply, the maximum field-induced electric polarization is reduced from 320 μC/m2 (x = 0) to 10 μC/m2 (x = 0.1). The results reveal that Dy plays a crucial role in the origin of the large linear magnetoelectric effect of DyCrO4, so chemical doping on this site provides an effective method to manipulate the magnetodielectric and magnetoelectric properties.

Magnetoelectric effects in multiferroic Y-type hexaferrites Ba0.3Sr1.7CoxMg2−xFe12O22**Project supported by the National Natural Science Foundation of China (Grant No. 51725104) and Beijing Natural Science Foundation, China (Grant No. Z180009).

Y-type hexaferrites with tunable conical magnetic structures are promising single-phase multiferroics that exhibit large magnetoelectric effects. We have investigated the influence of Co substitution on the magnetoelectric properties in the Y-type hexaferrites Ba0.3Sr1.7CoxMg2−xFe12O22 (x = 0.0, 0.4, 1.0, 1.6). The spin-induced electric polarization can be reversed by applying a low magnetic field for all the samples. The magnetoelectric phase diagrams of Ba0.3Sr1.7CoxMg2−xFe12O22 are obtained based on the measurements of magnetic field dependence of dielectric constant at selected temperatures. It is found that the substitution of Co ions can preserve the ferroelectric phase up to a higher temperature, and thus is beneficial for achieving single-phase multiferroics at room temperature.

Enhancement of magnetoelectric coupling by insertion of Co atomic layer into Fe3Si/BaTiO3(001) interfaces identified by first-principles calculations

The insertion of a Co single atomic layer into multiferroic interfaces is examined from first principles taking interfaces between BaTiO3 and Fe3Si as an example. We demonstrate that insertion of a Co atomic layer strongly prevents Si from being exposed to the interface. This protecting effect of Co makes the interface magnetoelectric constant of Fe3Si/Co/BaTiO3(001) remarkably large with 1.4 as, which makes contrast with the reduction of the interface multiferroicity by Si at the Fe3Si/BaTiO3(001) interface. The stability of the Co monolayer and the origin of the large magnetoelectric effect are clarified.

Large linear magnetoelectric effect and field-induced ferromagnetism and ferroelectricity in DyCrO4

All the magnetoelectric properties of scheelite-type DyCrO4 are characterized by temperature- and field-dependent magnetization, specific heat, permittivity, electric polarization, and neutron diffraction measurements. Upon application of a magnetic field within ±3 T, the nonpolar collinear antiferromagnetic structure leads to a large linear magnetoelectric effect with a considerable coupling coefficient. An applied electric field can induce the converse linear magnetoelectric effect, realizing magnetic field control of ferroelectricity and electric field control of magnetism. Furthermore, a higher magnetic field (>3 T) can cause a metamagnetic transition from the initially collinear antiferromagnetic structure to a canted structure, generating a large ferromagnetic magnetization up to 7.0 μB f.u.−1. Moreover, the new spin structure can break the space inversion symmetry, yielding ferroelectric polarization, which leads to coupling of ferromagnetism and ferroelectricity with a large ferromagnetic component.

Ferroelectromagnetic pseudocubic BiFeO3-LaFeO3-PbFeO2.5: Leakage current, dielectric, and multiferroic properties at room temperature

The ternary solid solution 0.6BiFeO3-0.1LaFeO3-0.3PbFeO2.5 (0.6BFO-0.1LFO-0.3PFO) was studied to determine the origin of spontaneous magnetization and electrical properties for the development of single-phase ferroelectromagnetics. Rietveld refinement of the X-ray diffraction pattern of 0.6BFO-0.1LFO-0.3PFO ceramics reveals a pseudocubic structure. Investigation of the leakage current density revealed different conduction mechanisms at different electric fields. Dielectric loss as a function of frequency (log δ-f plot) was affected by the grain size and grain boundaries. The coexistence of ferromagnetism and ferroelectricity was observed; a pulsed remanent polarization of 0.4 μC/cm2, remanent magnetization of 0.5 emu/g, and saturation magnetization of 3 emu/g were determined for 0.6BFO-0.1LFO-0.3PFO. A large magnetoelectric coupling effect of 120 mV/cm·Oe was observed.

Giant non-volatile magnetoelectric effects via growth anisotropy in Co40Fe40B20 films on PMN-PT substrates

Uniaxial magnetic anisotropy was imposed on a CoFeB film by applying an in-plane magnetic field during growth. Electrically driven strain from a ferroelectric 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 (011) substrate resulted in giant magnetoelectric effects, whose coupling constant peaked at a record value of ∼8.0 × 10−6 s m−1. These large magnetoelectric effects arose due to non-volatile 90° rotations of the magnetic easy axis, reflecting a competition between the fixed growth anisotropy and the voltage-controlled magnetoelastic anisotropy. In contrast to previous work, our non-volatile rotations did not require the assistance of an applied magnetic field or the setting of an in-plane substrate polarization prior to deposition.

Large Magnetoelectric Effects in Electrodeposited Nanoporous Microdisks Driven by Effective Surface Charging and Magneto-Ionics.

A synergetic approach to enhance magnetoelectric effects (i.e., control of magnetism with voltage) and improve energy efficiency in magnetically actuated devices is presented. The investigated material consists of an ordered array of Co-Pt microdisks, in which nanoporosity and partial oxidation are introduced during the synthetic procedure to synergetically boost the effects of electric field. The microdisks are grown by electrodeposition from an electrolyte containing an amphiphilic polymeric surfactant. The bath formulation is designed to favor the incorporation of oxygen in the form of cobalt oxide. A pronounced reduction of coercivity (88%) and a remarkable increase of Kerr signal amplitude (60%) are observed at room temperature upon subjecting the microdisks to negative voltages through an electrical double layer. These large voltage-induced changes in the magnetic properties of the microdisks are due to (i) the high surface-area-to-volume ratio with ultranarrow pore walls (sub-10 nm) that promote enhanced electric charge accumulation and (ii) magneto-ionic effects, where voltage-driven O2- migration promotes a partial reduction of CoO to Co at room temperature. This simple and versatile procedure to fabricate patterned "nano-in-micro" magnetic motifs with adjustable voltage-driven magnetic properties is very appealing for energy-efficient magnetic recording systems and other magnetoelectronic devices.

Spin-driven ferroelectricity and large magnetoelectric effect in monoclinic MnSb2S4

We report a spin-driven ferroelectricity below the helical spin ordering temperature in a nonoxide mineral $\mathrm{MnS}{\mathrm{b}}_{2}{\mathrm{S}}_{4}$, which crystallizes in a centrosymmetric monoclinic $\mathrm{HgB}{\mathrm{i}}_{2}{\mathrm{S}}_{4}$ structure. At $\mathrm{T}\ensuremath{\sim}25\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, the dielectric constant shows an anomaly and the spontaneous electric polarization begins to develop. The polarization obtained from pyroelectric current measurement can be switched by reversing the direction of poling electric field. Interestingly, upon applying magnetic field parallel to the electric field, the polarization is enhanced nearly six times above a critical field $H||E\ensuremath{\sim}5\phantom{\rule{0.16em}{0ex}}\mathrm{T}$, demonstrating large magnetoelectric effect in this system. Below $\mathrm{T}\ensuremath{\sim}25\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, this compound is known to exhibit an unusual magnetic structure where the spiral spins lie in the ac plane but propagate along the $b$ axis with an angle of $\ensuremath{\sim}{133}^{\ensuremath{\circ}}$ between the adjacent magnetic moments. The origin of ferroelectric ordering has been attributed to the inverse Dzyaloshinskii-Moriya type interaction in accordance with local symmetry considerations.