Electric Field Control Research Articles

Enhancement of spin Hall angle in semimetallic materials α -Sn under voltage regulation

Utilizing current-induced spin–orbit torque (SOT) to control magnetization is essential for the advancement of spintronics. SOT offers high energy efficiency and rapid operation speed. The ideal SOT material should have a high charge-to-spin conversion efficiency and excellent electrical conductivity. Recently, there has been a focus on topological insulator materials with topological surface states in SOT research due to their controllability in spin–orbit coupling, conductivity, and energy band topology. While topological Dirac semimetallic materials show promise for SOT applications, research on voltage regulation of their spin Hall angle is still in its early stages. This paper investigates the multilayer structure of a Dirac semimetallic material. In an α-Sn/Ag bilayer, the voltage regulation effect can increase the spin Hall angle by five times by adjusting the strain on the Fermi level. Experiments explore the role of a silver layer as a transport layer in the electric field control of multilayer films. This material system can enhance its effects under electric field regulation and offer insight for achieving regulation in new spintronic devices.

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.

Electric field control of the energy gap in ZnO and BaSnO3 films grown on PMN-PT

ZnO and BaSnO3 (BSO) thin films grown on Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) substrates have been studied using electrical resistance and photoconductivity (PC) spectra measurements under different applied electric fields on the substrate. The behavior of the resistance and the energy gap (EG) extracted from the PC spectra are modified by the polarization state of the substrate in the case of the ZnO film, while for BSO, these physical parameters depend on the strain imposed by the substrate when a voltage is applied on the PMN-PT. In the latter case, an in-plane tensile (compressive) strain leads to a reduction (increase) in the resistance and the energy gap when an external electric field is applied on the substrate. The behavior of ZnO and BSO can be explained by the different crystalline structure in both films and by the fact that ZnO is also a piezoelectric material. In ZnO, a change in the polarization state of the substrate is associated with an imposed strain and an induced polarization on the film that leads to a modification of the band bending and hence of the energy gap. In the case of BSO, a shift of the impurity and conduction band generates a modification of the energy gap for the different types of strain.

Electric field enhancement of the superconducting spin-valve effect via strain-transfer across a ferromagnetic/ferroelectric interface

In a ferromagnet/superconductor/ferromagnet (F/S/F) superconducting spin-valve (SSV), a change in the magnetization alignment of the two F layers modulates the critical temperature (Tc) of the S layer. The Tc-switching effect (the SSV effect) is based on the interplay between superconductivity and magnetism. The fast and large resistive switching associated with Tc-switching is suitable for nonvolatile cryogenic memory applications. However, the external magnetic field-based operation of SSVs is hindering their miniaturization, and therefore, electric field control of the SSV effect is desired. Here, we report epitaxial growth of a La0.67Ca0.33MnO3/YBa2Cu3O7/La0.67Ca0.33MnO3 SSV on a piezo-electric [Pb(Mg0.33Nb0.67)O3]0.7-[PbTiO3]0.3 (001) substrate and demonstrate electric field control of the SSV effect. Electric field-induced strain-transfer from the piezo-electric substrate increases the magnetization and Tc of the SSV and leads to an enhancement of the magnitude of Tc-switching. The results are promising for the development of magnetic-field-free superconducting spintronic devices, in which the S/F interaction is not only sensitive to the magnetization alignment but also to an applied electric field.

Electric field control of spin-orbit torque in annealed Ta/CoFeB/HfO x heterostructures via interfacial oxidation modulation

Electric field control of spin-orbit torque (SOT) exhibits promising potential in advanced spintronic devices through interfacial modulation. In this work, we investigate the influence of electric field and interfacial oxidation on SOT efficiency in annealed Ta/CoFeB/HfO x heterostructures. By varying annealing temperatures, the damping-like SOT efficiency reaches its peak at the annealing temperature of 320 °C, with an 80% field-free magnetization switching ratio induced by SOT having been demonstrated. This enhancement is ascribed to the annealing-induced modulation of oxygen ion migration at the CoFeB/HfO x interface. By applying voltages across the Ta/CoFeB/HfO x heterostructures, which drives the O2‒ migration across the interface, a reversible, bipolar, and non-volatile modulation of SOT efficiency was observed. The collective influence of annealing temperature and electric field effects on SOT carried out in this work provides an effective approach into facilitating the optimization and control of SOT in spintronic devices.

Electric field control of a quantum spin liquid in weak Mott insulators

Electric field control of a quantum spin liquid in weak Mott insulators

Novel 3D textile structures and geometries for electrofluidics.

The integration of microfluidics with electric field control, commonly referred to as electrofluidics, has led to new opportunities for biomedical analysis. The requirement for closed microcapillary channels in microfluidics, typically formed via complex microlithographic fabrication approaches, limits the direct accessibility to the separation processes during conventional electrofluidic devices. Textile structures provide an alternative and low-cost approach to overcome these limitations via providing open and surface-accessible capillary channels. Herein, we investigate the potential of different 3D textile structures for electrofluidics. In this study, 12 polyester yarns were braided around nylon monofilament cores of different diameters to produce functional 3D core-shell textile structures. Capillary electrophoresis performances of these 3D core-shell textile structures both before and after removing the nylon core were evaluated in terms of mobility and bandwidth of a fluorescence marker compound. It was shown that the fibre arrangement and density govern the inherent capillary formation within these textile structures which also impacts upon the solute analyte mobility and separation bandwidth during electrophoretic studies. Core-shell textile structures with a 0.47mm nylon core exhibited the highest fluorescein mobility and presented a narrower separation bandwidth. This optimal textile structure was readily converted to different geometries via a simple heat-setting of the central nylon core. This approach can be used to fabricate an array of miniaturized devices that possess many of the basic functionalities required in electrofluidics while maintaining open surface access that is otherwise impractical in classical approaches.

Stabilizing perpendicular magnetic anisotropy with strong exchange bias in PtMn/Co by magneto-ionics

Electric field control of magnetic properties offers a broad and promising toolbox for enabling ultra-low power electronics. A key challenge with high technological relevance is to master the interplay between the magnetic anisotropy of a ferromagnet and the exchange coupling to an adjacent antiferromagnet. Here, we demonstrate that magneto-ionic gating can be used to achieve a very stable out-of-plane (OOP) oriented magnetization with strong exchange bias in samples with as-deposited preferred in-plane (IP) magnetization. We show that the perpendicular interfacial anisotropy can be increased by more than a factor 2 in the stack Ta/Pt/PtMn/Co/HfO2 by applying −2.5 V gate voltage over 3 nm HfO2, causing a reorientation of the magnetization from IP to OOP with a strong OOP exchange bias of more than 50 mT. Comparing two thicknesses of PtMn, we identify a notable trade-off: while thicker PtMn yields a significantly larger exchange bias, it also results in a slower response to ionic liquid gating within the accessible gate voltage window. These results pave the way for post-deposition electrical tailoring of magnetic anisotropy and exchange bias in samples requiring significant exchange bias.

Voltage Control of Multiple Electrochemical Processes during Lithium Ion Migration in NiFe2O4 Ferrite.

Li-ion-based electric field control has been attracting significant attention, since it is able to penetrate deep into materials to exhibit diverse and controllable electrochemical processes, which offer more degrees of freedom to design multifunctional devices with low power consumption. As opposed to previous studies that mainly focused on single lithiation/delithiation mechanisms, we reveal three Li-ion modulation mechanisms in the same NiFe2O4 spinel ferrite by in situ magnetometry, i.e., intercalation, conversion, and space charge, which are respectively demonstrated in high, medium, and low voltage range. During the intercalation stage, the spinel structure is preserved, and a reversible modulation of magnetization arises from the charge transfer-induced variation of Fe valence states (Fe2+/Fe3+). Conversion-driven change in magnetization is the largest up to 89 emu g-1, due to the structural and magnetic phase transitions. Although both intercalation and conversion exhibit sluggish kinetics and long response times, the space charge manifests a faster switching speed and superior durability due to its interface electrostatic effect. These results not only provide a clear and comprehensive understanding on Li-based modulation mechanisms but also facilitate multifunctional and multiscenario applications, such as multistate memory, micromagnetic actuation, artificial synapse, and energy storage.

Electric field control of 180° magnetization reversal in a spin-valve multiferroic heterostructure

Electrical tuning of magnetism, rather than a spin current or magnetic field, has attracted much attention due to its great potential for designing energy-efficient spintronic devices. However, pure electric field (E-field) control of 180° magnetization reversal is still challenging. Thus, we report an E-field-controlled 180° magnetization reversal in a spin valve (SV)/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) multiferroic heterostructure. Via the converse magnetoelectric coupling effect in CoFe/PMN-PT heterostructures, the magnetic anisotropy and coercive field of the CoFe film can be tremendously modulated by an E-field. We fabricated an optimized SV grown on the PMN-PT substrate, in which the magnetic moments of the free and pinned layers are parallel to each other at the initial state. By applying an E-field, the coercive field of the free layer was enhanced, exhibiting an antiparallel configuration between the free and pinned layers. Based on the theoretical and experimental results, a complete 180° magnetization reversal of the free layer can be obtained without a magnetic field. Accordingly, an E-field-controlled giant, reversible and repeatable magnetoresistance modulation can be achieved. This work proposes a feasible strategy to achieve E-field-controlled 180° magnetization reversal, which is critical for exploring ultralow power consumption magnetic memory devices.

Electrical Control Grain Dimensionality with Multilevel Magnetic Anisotropy.

In alignment with the increasing demand for larger storage capacity and longer data retention, the electrical control of magnetic anisotropy has been a research focus in the realm of spintronics. Typically, magnetic anisotropy is determined by grain dimensionality, which is set during the fabrication of magnetic thin films. Despite the intrinsic correlation between magnetic anisotropy and grain dimensionality, there is a lack of experimental evidence for electrically controlling grain dimensionality, thereby impairing the efficiency of magnetic anisotropy modulation. Here, we demonstrate an electric field control of grain dimensionality and prove it as the active mechanism for tuning interfacial magnetism. The reduction in grain dimensionality is associated with a transition from ferromagnetic to superparamagnetic behavior. We achieve a nonvolatile and reversible modulation of the coercivity in both the ferromagnetic and superparamagnetic regimes. Subsequent electrical and elemental analysis confirms the variation in grain dimensionality upon the application of gate voltages, revealing a transition from a multidomain to a single-domain state, accompanied by a reduction in grain dimensionality. Furthermore, we exploit the influence of grain dimensionality on domain wall motion, extending its applicability to multilevel magnetic memory and synaptic devices. Our results provide a strategy for tuning interfacial magnetism through grain size engineering for advancements in high-performance spintronics.

Photon-Dipole-Spin Interactions in M(TCNE)x/P(VDF-TrFE) Multiferroic Heterostructure Available for Bimodal Control of Multistate Data-Storage.

Organic multiferroic heterostructure is one of the most promising structures for the future design of high-density flexible energy-efficient data storage. Here, organic ferromagnetic metal(tetracyanoethylene) (M(TCNE))x/ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) multiferroic heterostructures are fabricated, where the excited state in M(TCNE)x interacted with localized dipole in P(VDF-TrFE) provides a key link for the interfacial coupling. Thus, aligned dipoles in P(VDF-TrFE) by external electric field can affect the magnetization of Fe(TCNE)x effectively to result in a pronounced magnetization-voltage (M-V) hysteresis loop. Moreover, light-induced electron-hole pairs in Fe(TCNE)x with long lifetime effectively interact with the dipoles in P(VDF-TrFE) to lead to an effect in external light control of electric polarization of P(VDF-TrFE). Overall, the organic multiferroic heterostructure provides the possibility of realizing two storage modes, light control of dipole as well as electric field control of spin, which can broaden multifunctional applications of organic multiferroic materials in the area of multistate storage.

Coherent electric field control of orbital state of a neutral nitrogen-vacancy center

The coherent control of the orbital state is crucial for realizing the extremely-low power manipulation of the color centers in diamonds. Herein, a neutrally-charged nitrogen-vacancy center, NV0, is proposed as an ideal system for orbital control using electric fields. The electric susceptibility in the ground state of NV0 is estimated, and found to be comparable to that in the excited state of NV−. Also, the coherent control of the orbital states of NV0 is demonstrated. The required power for orbital control is three orders of magnitude smaller than that for spin control, highlighting the potential for interfacing a superconducting qubit operated in a dilution refrigerator.

In situ electric-field control of ferromagnetic resonance in the low-loss organic-based ferrimagnet V[TCNE]x∼2

We demonstrate indirect electric-field control of ferromagnetic resonance (FMR) in devices that integrate the low-loss, molecule-based, room-temperature ferrimagnet vanadium tetracyanoethylene (V[TCNE]x∼2) mechanically coupled to PMN-PT piezoelectric transducers. Upon straining the V[TCNE]x films, the FMR frequency is tuned by more than 6 times the resonant linewidth with no change in Gilbert damping for samples with α = 6.5 × 10−5. We show this tuning effect is due to a strain-dependent magnetic anisotropy in the films and find the magnetoelastic coefficient |λs| ∼ (1–4.4) ppm, backed by theoretical predictions from density-functional theory calculations and magnetoelastic theory. Noting the rapidly expanding application space for strain-tuned FMR, we define a new metric for magnetostrictive materials, magnetostrictive agility, given by the ratio of the magnetoelastic coefficient to the FMR linewidth. This agility allows for a direct comparison between magnetostrictive materials in terms of their comparative efficacy for magnetoelectric applications requiring ultra-low loss magnetic resonance modulated by strain. With this metric, we show V[TCNE]x is competitive with other magnetostrictive materials, including YIG and Terfenol-D. This combination of ultra-narrow linewidth and magnetostriction, in a system that can be directly integrated into functional devices without requiring heterogeneous integration in a thin film geometry, promises unprecedented functionality for electric-field tuned microwave devices ranging from low-power, compact filters and circulators to emerging applications in quantum information science and technology.

Nonreciprocal and Nonvolatile Electric-Field Switching of Magnetism in van der Waals Heterostructure Multiferroics.

Multiferroic materials provide robust and efficient routes for the control of magnetism by electric fields, which have been diligently sought after for a long time. Construction of two-dimensional (2D) vdW multiferroics is a more exciting endeavor. To date, the nonvolatile manipulation of magnetism through ferroelectric polarization still remains challenging in a 2D vdW heterostructure multiferroic. Here, we report a van der Waals (vdW) heterostructure multiferroic comprising the atomically thin layered antiferromagnet (AFM) CrI3 and ferroelectric (FE) α-In2Se3. We demonstrate anomalously nonreciprocal and nonvolatile electric-field control of magnetization by ferroelectric polarization. The nonreciprocal electric control originates from an intriguing antisymmetric enhancement of interlayer ferromagnetic coupling in the opposite ferroelectric polarization configurations of α-In2Se3. Our work provides numerous possibilities for creating diverse heterostructure multiferroics at the limit of a few atomic layers for multistage magnetic memories and brain-inspired in-memory computing.

Electric-field control of nonvolatile resistance state of perpendicular magnetic tunnel junction via magnetoelectric coupling.

Magnetic tunnel junctions (MTJs) are the core elements of spintronic devices. Now, the mainstream writing operation of MTJs mainly relies on electric current with high energy dissipation, which can be greatly reduced if an electric field is used instead. In this regard, strain-mediated multiferroic heterostructure composed of MTJ and ferroelectrics are promising with the advantages of room temperature and magnetic field-free as already demonstrated by MTJ with in-plane magnetic anisotropy. However, there is no such report on the perpendicular MTJs (p-MTJs), which have been commercialized. Here, we investigate electric-field control of resistance state of MgO-based p-MTJs in multiferroic heterostructures. A remarkable and nonvolatile manipulation of resistance is demonstrated at room temperature without magnetic field assistance. Through various characterizations and micromagnetic simulation, the manipulation mechanism is uncovered. Our work provides an effective avenue for manipulating p-MTJ resistance by electric fields and is notable for high density and ultralow power spintronic devices.

A universal strategy for electric field control of nonvolatile magnetization reversal

Achieving electric field control of nonvolatile magnetization reversal in van der Waals magnetic tunnel junctions (vdW MTJs) is of paramount importance for nanoscale spintronic devices with ultralow-power consumption and high-density storage. Here, a new and universal design strategy is proposed to realize nonvolatile magnetization reversal, which is based on electric field control of interlayer coupling. The nonvolatility benefits from the proposed special principle of vdW MTJ, in which the dependence of interlayer coupling energy on electric field strength follows a continuous odd function in mathematics. The feasibility of proposed strategy is proved by the MnBi2Te4/h-BN/Fe3GaTe2/h-BN/MnBi2Te4 junction. The magnetization state of Fe3GaTe2 can be reversed 180° by changing electric field directions. Moreover, the magnetization states can be preserved after removing electric field, demonstrating the nonvolatile magnetization reversal. Therefore, the present strategy provides an alternative approach to realize electric control of nonvolatile magnetization reversal in vdW MTJs for next-generation spintronic devices.

Nonvolatile Electric Control of Antiferromagnet CrSBr.

van der Waals magnets are emerging as a promising material platform for electric field control of magnetism, offering a pathway toward the elimination of external magnetic fields from spintronic devices. A further step is the integration of such magnets with electrical gating components that would enable nonvolatile control of magnetic states. However, this approach remains unexplored for antiferromagnets, despite their growing significance in spintronics. Here, we demonstrate nonvolatile electric field control of magnetoelectric characteristics in van der Waals antiferromagnet CrSBr. We integrate a CrSBr channel in a flash-memory architecture featuring charge trapping graphene multilayers. The electrical gate operation triggers a nonvolatile 200% change in the antiferromagnetic state of CrSBr resistance by manipulating electron accumulation/depletion. Moreover, the nonvolatile gate modulates the metamagnetic transition field of CrSBr and the magnitude of magnetoresistance. Our findings highlight the potential of manipulating magnetic properties of antiferromagnetic semiconductors in a nonvolatile way.

Electric field control of perpendicular magnetic tunnel junctions with easy-cone magnetic anisotropic free layers.

Magnetic tunnel junctions (MTJs) are the core element of spintronic devices. Currently, the mainstream writing operation of MTJs is based on electric current with high energy dissipation, and it can be notably reduced if an electric field is used instead. In this regard, it is promising for electric field control of MTJ in the multiferroic heterostructure composed of MTJ and ferroelectrics via strain-mediated magnetoelectric coupling. However, there are only reports on MTJs with in-plane anisotropy so far. Here, we investigate electric field control of the resistance state of MgO-based perpendicular MTJs with easy-cone anisotropic free layers through strain-mediated magnetoelectric coupling in multiferroic heterostructures. A remarkable, nonvolatile, and reversible modulation of resistance at room temperature is demonstrated. Through local reciprocal space mapping under different electric fields for Pb(Mg1/3Nb2/3)0.7Ti0.3O3 beneath the MTJ pillar, the modulation mechanism is deduced. Our work represents a crucial step toward electric field control of spintronic devices with non-in-plane magnetic anisotropy.

Study on the as-cast microstructure and mechanical properties of 35CrMo steel based on electric field control

Herein, the effect of current on the solidification microstructure and properties of 35CrMo structural steel has been studied. The effect of an electric field on the solidification structure of an ingot was investigated by immersing two parallel electrodes into the free surface of molten steel. Using the interaction between the current and melt as well as the Lorentz force generated by its own induced magnetic field, the whole region of the melt was covered with an eddy current. The numerical simulation of the ingot solidification process has been carried out and its influence on the inner flow field during the ingot solidification control process discussed. The results showed that an applied electric field caused turbulence inside the ingot, which drove the molten alloys to rotate and stir, refined the solidification structure, reduced the solidification defects, such as shrinkage cavity and segregation, and increased from 549.9 MPa at the top edge of the ingot and 411.4 MPa at the middle edge to 560.2 and 510.2 MPa, respectively. In addition, the electric field made the hardness and strength of each part of the ingot more uniform and improved the quality of its rigidity for the steel production process.