Electrical Control Of Magnetic Properties Research Articles

Recent advances in electric field-controlled magnetism using perovskite multiferroic heterostructures for spintronics applications

This review article presents the recent advances in electric field-controlled magnetism using multiferroic heterostructures. Electric field-manipulated spin magnetic moments are important from both basic science and application points of view. Multiferroic materials, where ferroelectricity and magnetic orderings coexist, offer exciting and novel prospects of electric control of magnetic properties. Electric field control of magnetism is essential to developing energy-efficient and versatile spintronic devices that can revolutionize data storage, magnetic sensing, and many other applications. Thus, we will review recent progress in electric field control of magnetism in multiferroic heterostructures and its advanced characterization to identify potential applications, remaining challenges, and future prospects. Through this review, we hope the reader will gain knowledge on the recent advances in electric field-controlled magnetism and its challenges that can lead to the practical realization of new generation devices in the future.

Control of Compensation Temperature in CoGd Films through Hydrogen and Oxygen Migration under Gate Voltage.

Electrical control of magnetic properties is crucial for low-energy memory and logic spintronic devices. We find that the magnetic properties of ferrimagnetic CoGd can be altered through ionic liquid gating. Gate voltages manipulate the opposite magnetic moments in Co and Gd sublattices and induce a giant magnetic compensation temperature change of more than 200 K in Pt/CoGd/Pt heterostructures. The electrically controlled dominant magnetic sublattice allows voltage-induced magnetization switching. Both experiments and theoretical calculations demonstrate that the significant modulations of compensation temperature are relevant to the reduced Gd moments due to the presence of hydrogen ions at positive voltages as well as the enhanced Co moments and reduced Gd moments due to the injection of oxygen ions at negative voltages. These findings expand the possibilities for all-electric and reversible magnetization control in the field of spintronics.

Ferroelectric polarization tailored interfacial charge distribution to modify magnetic properties of two-dimensional Janus FeBrI/In2S3 heterostructures

The discovery of two-dimensional magnetic and ferroelectric materials provides a feasible opportunity to realize the nonvolatile electrical control of magnetic properties in van der Waals multiferroic heterostructures. Here, based on the density of functional theory, we study the electronic structures and magnetic properties of the Janus FeBrI/In2S3 multiferroic heterostructure. The Curie temperature and magnetic anisotropy energy (MAE) can be modulated by the ferroelectric polarization due to the interfacial charge redistribution. According to the orbital-resolved magnetocrystalline anisotropy energy (EMCA) and the second-order perturbation theory, the difference of EMCA mainly stems from the change in electronic states near the Fermi level, which is associated with interfacial charge redistribution in different ferroelectric polarization directions. These findings not only reveal the physical mechanism of the change of MAE in detail but also suggest a feasible strategy to modulate the magnetic properties.

Electric control of magnetic properties in epitaxially grown FeRh/MgO/PMN-PT heterostructures

We epitaxially grew the metamagnetic FeRh films on ferroelectric PMN-PT(001) substrates and investigated the electric control of magnetic properties. An MgO buffer layer is inserted to reduce the considerably large lattice mismatch of 5.44% between FeRh and PMN-PT, leading to a nice epitaxial growth with a relationship of FeRh[110](001)||MgO[100](001)||PMN-PT[100](001). The as-grown FeRh film shows a typical antiferromagnetic-to-ferromagnetic phase transition by means of varying the temperature. Because a growth-induced uniaxial magnetic anisotropy is superimposed on the in-plane four-fold magnetocrystalline anisotropy, the epitaxial FeRh film displays different kinds of multi-step hysteresis loops at various field orientations. An electric field applied on the PMN-PT substrate can remarkably increase the coercivity of FeRh film, which presents a butterfly type shape, indicating a strain-mediated magnetoelectric coupling. Because of the inhibitory effect of the remnant compressive strain on the phase transition, the critical transition temperature and the magnetization are obviously enhanced and reduced, respectively, after removing the electric effect.

Ferroelectric control of single-molecule magnetism in 2D limit

The electric control of magnetic properties based on magnetoelectric effect is crucial for the development of future data storage devices. Here, based on first-principles calculations, a strong magnetoelectric effect is proposed to effectively switch on/off the magnetic states as well as alter the in-plane/perpendicular easy axes of metal-phthalocyanine molecules (MPc) by reversing the electric polarization of the underlying two-dimensional (2D) ferroelectric α-In2Se3 substrate with the application of an external electric field. The mechanism originates from the different hybridization between the molecule and the ferroelectric substrate in which the different electronic states of surface Se layer play a dominant role. Moreover, the magnetic moments and magnetic anisotropy energies (MAE) of OsPc/In2Se3 can be further largely enhanced by a functionalized atom atop the OsPc molecule. The I-OsPc/In2Se3 system possesses large MAE up to 30 meV at both polarization directions, which is sufficient for room-temperature applications. These findings provide a feasible scheme to realize ferroelectric control of magnetic states in 2D limit, which have great potential for applications in nanoscale electronics and spintronics.

Charge-Transfer-Induced Interfacial Exchange Coupling at the Co/BiFeO3 Interface

The interplay between ferroelectricity and magnetism in multiferroic materials is of great scientific and technological interest, allowing magnetic control of ferroelectric properties and electric control of magnetic properties through the magnetoelectric coupling from interfacial strain, exchange bias, or charge-transfer process. We report the charge transfer at the Co/BiFeO3 interface from which the interfacial exchange coupling is achieved with the formation of Fe2+. The x-ray linear dichroism and x-ray magnetic circular dichroism results reveal that the strain as well as the exchange coupling J(ex) in BiFeO3 (BFO) with periodic 109 degrees domains are stronger than that in BFO with 71 degrees domains, resulting in the higher coercive field of Co/BFO with 109 degrees domain samples. The possible electric field control of the charge-transfer process at the Co/BFO interface enables an alternative class of electrically controllable magnetization, exchange bias, and giant magnetoresistive response of spintronic devices.

Electric field control of magnetic properties in FeRh/PMN-PT heterostructures

We investigated electric control of magnetic properties in FeRh/PMN-PT heterostructures. An electric field of 1 kV/cm applied on the PMN-PT substrate could increase the coercivity of FeRh film from 60 to 161 Oe at 360 K where the FeRh antiferromagnetic to ferromagnetic phase transition occurs. The electric field dependent coercive field reveals a butterfly shape, indicating a strain-mediated magnetoelectric coupling across the FeRh/PMN-PT interface. However, the uniaxial magnetic anisotropy of FeRh is almost unchanged with the applied electric field on the PMN-PT substrate, which suggests the change of coercivity in FeRh films is mainly due to the shift of the magnetic transition temperature under the electric field.

Magnetoelectric coupling and external field modulation of a composite multiferroic chain

Multiferroics, can simultaneously exhibit multiple ferroic orders, including magnetic order, electric order and elastic order. Among these orders there exist intimately coupling effects. Multiferroics is significant for technological applications and fundamental research. The interplay between ferroelectricity and magnetism allows a magnetic control of ferroelectric properties and an electric control of magnetic properties, which can yield new device concepts. Recent experimental research shows that the Fe/BaTiO<sub>3</sub> compound exhibits a prominent magnetoelectric effect, which originates from a change in bonding at the ferroelectric-ferromagnet interface that changes the interface magnetization when the electric polarization reverses, and thus offering a new route to controlling the magnetic properties of multilayer compound heterostructures by the electric field. Motivated by recent discoveries, in this paper we investigate theoretically the thermodynamics of a finite ferroelectric-ferromagnetic chain. A microscopic Heisenberg spin model is constructed to describe magnetoelectric properties of this composite chain, in which electric and magnetic subsystem are coupled through interfacial coupling. However, this vector model is not integrable in general. Therefore, one has to resort to numerical calculations for the thermodynamic properties of such a system. A uniform discrete spin vector is adopted here to approximate the original continuous one, and then the transfer-matrix method is employed to derive the analytical expression. To verify its rationality and effectiveness, the zero-field specific heat of a classical spin chain is solved based on this simplified model, and compared with the exact solution. It demonstrates that the main characteristics obtained by previous research are well reproduced here, and the whole variant trend is also identical. And then the quantities concerned in this paper are calculated, including the magnetization, polarization, magnetoelectric susceptibility, and specific heat. The influence of interfacial coupling, external field, and single-ion anisotropy on the magnetoelectric effect of the composite chain are examined in detail. The results reveal that the interfacial coupling enhances the magnetization and polarization. And in the magnetic field driven magnetoelectric susceptibility, the large magnetoelectric correlation effects are observed, indicating that the magnetic behaviors can be effectively controlled by an external electric field. Meanwhile, it is also found that the external field and single-ion anisotropy both suppress the magnetoelectric susceptibility. In addition, interestingly, the specific heat of system presents a three-peak structure under high electric field, which stems from the thermal excitation of spin states as well as dipole moment caused jointly by electric field and temperature.

Nonlinear magnetoelectric effect in paraelectric state of Co4Nb2O9 single crystal

We report the structural, magnetoelectric (ME), magnetic and electric control of magnetic properties in Co4Nb2O9 (CNO) single crystal. A detailed ME measurement reveals a nonlinear ME effect instead of a linear ME effect in CNO single crystal. By fitting the magnetization-electric field (M-E) curve, it can be found that the linear ({alpha }_{e}) and quadratic (γ) coefficients equal to ~8.27 ps/m and ~−6.46 ps/MV for upper branch, as well as ~8.38 ps/m and ~6.75 ps/MV for the lower branch. More importantly, a pronounced response was observed under a small cooling magnetic field, which cannot even cause the spin flop. This suggests a magnetoelectric effect can occur at paraelectric state for CNO single crystal. Furthermore, we also found that the magnetization of every axis responds to electric field applied along a-axis, but fails to do so when the electric field is applied c-axis. Such findings supply a direct evidence to the magnetic structure and ME coupling mechanism indirectly reflected by our neutron experiment.

Spin-polarized current injection induced magnetic reconstruction at oxide interface

Electrical manipulation of magnetism presents a promising way towards using the spin degree of freedom in very fast, low-power electronic devices. Though there has been tremendous progress in electrical control of magnetic properties using ferromagnetic (FM) nanostructures, an opportunity of manipulating antiferromagnetic (AFM) states should offer another route for creating a broad range of new enabling technologies. Here we selectively probe the interface magnetization of SrTiO3/La0.5Ca0.5MnO3/La0.7Sr0.3MnO3 heterojunctions and discover a new spin-polarized current injection induced interface magnetoelectric (ME) effect. The accumulation of majority spins at the interface causes a sudden, reversible transition of the spin alignment of interfacial Mn ions from AFM to FM exchange-coupled, while the injection of minority electron spins alters the interface magnetization from C-type to A-type AFM state. In contrast, the bulk magnetization remains unchanged. We attribute the current-induced interface ME effect to modulations of the strong double-exchange interaction between conducting electron spins and local magnetic moments. The effect is robust and may serve as a viable route for electronic and spintronic applications.

Artificial multiferroic heterostructures for an electric control of magnetic properties

The control of magnetism by electric fields is an important goal for future low-power spintronics devices. This partly explains the intensified recent interest for magnetoelectric multiferroic materials and heterostructures. The lack of ferro- or ferrimagnetic–ferroelectric materials with large magnetoelectric coupling between the two orders has spurred intensive research on artificial multiferroics combining ferroelectric or piezoelectric materials and ferromagnets. In this paper we review synthetically the potential of thin-film-based heterostructures in which a magnetic film is in contact with a ferroelectric or piezoelectric one to obtain an electric control of magnetic properties. This electric control either results from a strain-induced magnetoelectric coupling, a charge-driven one, or from the modulation of an interfacial exchange-bias interaction. Contrôler électriquement les propriétés magnétiques des matériaux et réaliser ainsi de nouveaux composants faiblement consommateurs en énergie est un des enjeux de la future électronique de spin. Ceci explique l'intérêt considérable porté aux matériaux et architectures multiferroïques. Malgré des recherches intenses, le graal d'un composé à la fois ferroélectrique et ferro- ou ferrimagnétique à température ambiante avec un fort couplage magnétoélectrique entre ces deux propriétés n'a pas encore été trouvé. Pour pallier ce manque, de nombreux travaux ont porté sur les multiferroïques artificiels, hétérostructures combinant un matériau ferroélectrique ou piézoélectrique et un composé ferromagnétique. Cet article constitue une revue succincte du potentiel de ces hétérostructures en géométrie planaire pour obtenir un contrôle électrique des propriétés magnétiques. Un tel contrôle peut être obtenu par un effet magnétoélectrique indirect basé sur un couplage d'origine élastique, de façon directe par une modulation des charges dans le ferromagnétique induite par la ferroélectricité ou encore en exploitant le couplage d'échange à l'interface entre un multiferroïque et un matériau magnétique.

Electrical Writing of Magnetic and Resistive Multistates in CoFe Films Deposited Onto Pb[ZrxTi1-x]O3

Electric control of magnetic properties is an important challenge for modern magnetism and spintronic development. In particular, an ability to write magnetic state electrically would be highly beneficial. Among other methods, the use of electric field induced deformation of piezoelectric elements is a promising low-energy approach for magnetization control. We investigate the system of piezoelectric substrate Pb[ZrxTi1-x]O3 with CoFe overlayers, extending the known reversible bistable electro-magnetic coupling to surface and multistate operations, adding the initial state reset possibility. Increasing the CoFe thickness improves the magnetoresistive sensitivity, but at the expenses of decreasing the strain-mediated coupling, with optimum magnetic thin film thickness of the order of 100nm. The simplest resistance strain gauge structure is realized and discussed as a multistate memory cell demonstrating both resistive memory (RRAM) and magnetoresistive memory (MRAM) functionalities in a single structure.

Thermally assisted electric field control of magnetism in flexible multiferroic heterostructures.

Thermal and electrical control of magnetic anisotropy were investigated in flexible Fe81Ga19 (FeGa)/Polyvinylidene fluoride (PVDF) multiferroic heterostructures. Due to the large anisotropic thermal deformation of PVDF (α1 = −13 × 10−6 K−1 and α2 = −145 × 10−6 K−1), the in-plane uniaxial magnetic anisotropy (UMA) of FeGa can be reoriented 90° by changing the temperature across 295 K where the films are magnetically isotropic. Thus, the magnetization of FeGa can be reversed by the thermal cycling between 280 and 320 K under a constant magnetic field lower than coercivity. Moreover, under the assistance of thermal deformation with slightly heating the samples to the critical temperature, the electric field of ± 267 kV cm−1 can well align the UMA along the two orthogonal directions. The new route of combining thermal and electrical control of magnetic properties realized in PVDF-based flexible multiferroic materials shows good prospects in application of flexible thermal spintronic devices and flexible microwave magnetic materials.

Magnetoelectric Devices for Spintronics

The control of magnetism by electric fields is an important goal for the future development of low-power spintronics. Various approaches have been proposed on the basis of either single-phase multiferroic materials or hybrid structures in which a ferromagnet is influenced by the electric field applied to an adjacent insulator (usually having a ferroelectric, piezoelectric, or multiferroic character). The electric field effect on magnetism can be driven by purely electronic or electrostatic effects or can occur through strain coupling. Here we review progress in the electrical control of magnetic properties (anisotropy, spin order, ordering temperature, domain structure) and its application to prototype spintronic devices (spin valves, magnetic tunnel junctions). We tentatively identify the main outstanding difficulties and give perspectives for spintronics and other fields.

Magnetoelectric interfaces and spin transport

Engineered heterostructures designed for electric control of magnetic properties, the so-called magnetoelectric interfaces, present a novel route towards using the spin degree of freedom in electronic devices. Here, we review how a subset of such interfaces, namely ferromagnet-ferroelectric heterostructures, display electronically mediated control of magnetism and, in particular, emphasis is placed on how these effects manifest themselves as detectable spin-dependent transport phenomena. Examples of these effects are given for a variety of material systems on the basis of ferroelectric oxides, manganese and ruthenium magnetic complex oxides and elemental ferromagnetic metals. Results from both theory and experiment are discussed.

Electrical control of the ferromagnetic phase transition in cobalt at room temperature

Electrical control of magnetic properties is crucial for device applications in the field of spintronics. Although the magnetic coercivity or anisotropy has been successfully controlled electrically in metals as well as in semiconductors, the electrical control of Curie temperature has been realized only in semiconductors at low temperature. Here, we demonstrate the room-temperature electrical control of the ferromagnetic phase transition in cobalt, one of the most representative transition-metal ferromagnets. Solid-state field effect devices consisting of a ultrathin cobalt film covered by a dielectric layer and a gate electrode were fabricated. We prove that the Curie temperature of cobalt can be changed by up to 12 K by applying a gate electric field of about ±2 MV cm(-1). The two-dimensionality of the cobalt film may be relevant to our observations. The demonstrated electric field effect in the ferromagnetic metal at room temperature is a significant step towards realizing future low-power magnetic applications.

Tunability of magnetization in lateral few electron double quantum dots

We demonstrate theoretically a pathway for electrical control of magnetic properties of tunable lateral double InAs quantum dots containing two-electrons, subjected to spin-orbit interaction (SOI), vertical electrical and magnetic fields. In the regime of low temperature and weak magnetic field, interplay of interdot tunnel coupling and hybridized magnetoelectric effect induces “s”-like behavior of magnetization and a peak of susceptibility which are very sensitive to interdot barrier voltage (VB) and interdot distance (d). Sweeping VB and adjusting d not only impact magnetic phase transition, but also switch electronic and magnetic properties from atomic to molecular in nature. Furthermore, SOI broadens the magnetic field interval of paramagnetic phase and changes magnitude of magnetization and susceptibility.

Spin-Sensitive Conductance in Magnetically Contacted Graphene Flakes

The aim of this study is to gain a deeper insight into the impact of geometrical dimensions (aspect ratio) and current direction (zigzag vs. armchair) on transport characteristics. It is found that there is a pronounced dependence of the giant magnetoresistance (in setups with 2 ferromagnetic electrodes), as well as the spin polarization of current (in the case of one paramagnetic and one ferromagnetic electrode) on the bias and gate voltages, meaning a possible electrical control of magnetic properties of these quantities.