Interfacial Magnetoelectric Coupling Research Articles

First principles electron transport in magnetoelectric SrRuO3/BaTiO3/SrTiO3/SrRuO3interfaces.

Recently, all-oxide ferroelectric tunnel junctions, with single or composite potential barriers based on SrRuO3/BaTiO3/SrTiO3(SRO/BTO/STO) perovskites, have drawn a particular interest for high density low power applications, due to their highly tunable transport properties and device scaling down possibility to atomic size. Here, using first principles calculations and the NEGFs formalism, we explore the electronic structure and tunneling transport properties in magnetoelectric SRO/BTO/mSTO/SRO interfaces, (m= 0, 2, or 4 unit cells), considering both the RuO6octahedra tilts and magnetic SRO electrodes. Our main results may be summarized as follows: i) The band alignment schemes predict that polarization direction may determine both Schottky barrier or Ohmic contacts form(STO)=0, but only Schottky contacts form(STO)=2 and 4 junctions; ii) The tunnel electroresistance and tunnel magnetoresistance ratios are evaluated at 0 and 300 K; iii) The most magnetoelectric responsive interfaces are obtained for them(STO)=2 heterostructure, this system also showing co-existent giant tunnel electroresistance and tunnel magnetoresistance effects; iv) The interfacial magnetoelectric coupling is not strong enough to control the tunnel magnetoresistance by polarization switching, in spite of significant SRO ferromagnetism.

Visible-light controlled interfacial magnetoelectric coupling in SrRuO3/BaTiO3 heterostructure

Artificial multiferroics provide a tunable magnetoelastic and magnetoelectric coupling owing to the variety of combinations of ferroelectric and ferromagnetic layers, hence facilitate a better perspective for device applications such as magnetic field sensors and electric write magnetic -read memory devices. The intertwined physical properties can be controlled via external parameters such as electric field, temperature, and magnetic field. Here, we report an additional mode to manoeuvre the magnetoelastic and magnetoelectric coupling in an epitaxial SrRuO3/BaTiO3 multiferroic heterostructure using polarized visible light illumination. The light-induced ferroelastic (FE) domain wall motion in underlying BaTiO3 leads to photostriction and photodomain effects. Consequently, the change in the converse magnetoelastic effects leads to modify the magnetic properties of the above grown SrRuO3 layer. Besides this, we have observed a sharp and persistent changes in the SrRuO3/ BaTiO3 heterostructure, when the system is electrically biased owing to the change in the interfacial converse magnetoelectric coupling. Light controlled magnetization tunability in BaTiO3-based artificial multiferroic can open an alternate way for potential applications in several types of wireless devices and magnetic field sensors, electric write magnetic-read memory devices and other interesting optomechanical systems. Our findings in this context can be proven indeed as a novel prospective for opto-spintronics device applications.

Nonvolatile magnetoelectric coupling in two-dimensional van der Waals sandwich heterostructure CuInP2S6/MnCl3/CuInP2S6.

Electrical control of magnetism is of great interest for low-energy-consumption spintronic applications. Due to the recent experimental breakthrough in two-dimensional materials, with the absence of hanging bonds on the surface and strong tolerance for lattice mismatch, heterogeneous integration of different two-dimensional materials provides a new opportunity for coupling between different physical properties. Here, we report the realization of nonvolatile magnetoelectric coupling in vdW sandwich heterostructure CuInP2S6/MnCl3/CuInP2S6. Using first-principles calculations, we reveal that when interfacing with ferroelectric CuInP2S6, the Dirac half-metallic state of monolayer MnCl3 will be destroyed. Moreover, depending on the electrically polarized direction of CuInP2S6, MnCl3 can be a half-metal or a ferromagnetic semiconductor. We unveil that the obtained ferromagnetic semiconductor in MnCl3 can be attributed to the different gain and loss of electrons on the two adjacent Mn atoms due to the sublattice symmetry broken by interlayer coupling. The effects of interfacial magnetoelectric coupling on magnetic anisotropy and ferromagnetic Curie temperature of MnCl3 are also investigated, and a multiferroic memory based on this model is designed. Our work not only provides a promising way to design nonvolatile electrical control of magnetism but also renders monolayer MnCl3 an appealing platform for developing low-dimensional memory devices.

Ferroelectric control of band alignments and magnetic properties in the two-dimensional multiferroic VSe2/In2Se3

Our first-principles evidence shows that the two-dimensional (2D) multiferroic VSe2/In2Se3 experiences continuous change of electronic structures, i.e. with the change of the ferroelectric (FE) polarization of In2Se3, the heterostructure can possess type-I, -II, and -III band alignments. When the FE polarization points from In2Se3 to VSe2, the heterostructure has a type-III band alignment, and the charge transfer from In2Se3 into VSe2 induces half-metallicity. With reversal of the FE polarization, the heterostructure enters the type-I band alignment, and the spin-polarized current is turned off. When the In2Se3 is depolarized, the heterostructure has a type-II band alignment. In addition, influence of the FE polarization on magnetism and magnetic anisotropy energy of VSe2 was also analyzed, through which we reveal the interfacial magnetoelectric coupling effects. Our investigation about VSe2/In2Se3 predicts its wide applications in the fields of both 2D spintronics and multiferroics.

Reversal of the magnetoelectric effect at a ferromagnetic metal/ferroelectric interface induced by metal oxidation

Multiferroic materials composed of ferromagnetic and ferroelectric components are interesting for technological applications due to sizable magnetoelectric coupling allowing the control of magnetic properties by electric fields. Due to being compatible with the silicon-based technology, HfO2-based ferroelectrics could serve as a promising component in the composite multiferroics. Recently, a strong charge-mediated magnetoelectric coupling has been predicted for a Ni/HfO2 multiferroic heterostructure. Here, using density functional theory calculations, we systematically study the effects of the interfacial oxygen stoichiometry relevant to experiments on the magnetoelectric effect at the Ni/HfO2 interface. We demonstrate that the magnetoelectric effect is very sensitive to the interface stoichiometry and is reversed if an oxidized Ni monolayer is formed at the interface. The reversal of the magnetoelectric effect is driven by a strong Ni−O bonding producing exchange-split polarization-sensitive antibonding states at the Fermi energy. We argue that the predicted reversal of the magnetoelectric effect is typical for other 3d ferromagnetic metals, such as Co and Fe, where the metal-oxide antibonding states have an opposite spin polarization compared to that in the pristine ferromagnetic metals. Our results provide an important insight into the mechanism of the interfacial magnetoelectric coupling, which is essential for the physics and application of multiferroic heterostructures.

The dynamics of polarization and magnetization: Susceptibilities of magnetoelectric multiferroic heterostructure

The dynamic susceptibility is the crucial parameter of a material, especially when the material is needed to be applied in the electromagnetic applications. In this report, we discuss the magnetic and the electric susceptibilities of a magnetoelectric (ME) multiferroic heterostructure comprised of ferromagnetic (FM) and ferroelectric (FE) materials. Since the magnetoelectric couplings in multiferroic heterostructure have only existed at the interface between FM and FE, then the equation of motions in each lattice in every layer of FM and FE should be considered. The equations of motion in each lattice are solved simultaneously by employing entire-cell effective medium approximation. In numerical calculation, the parameters appropriate for Fe and BaTiO3 are used. We found that interfacial ME couplings shift down the resonance frequency for both FM and FE susceptibilities. We also noticed that the addition of the number of FE or FM layer, which raises the number of interface between FE and FM affects the susceptibility curves.

Self-assembled three-dimensional framework of PbTiO3:ε-Fe2O3 nanostructures with room temperature multiferroism

Hybrid multiferroic systems composed of complex oxides have drawn sustained attention for decades due to their intriguing physical effects and potential technological exploitations. Designing innovative nanostructures of multiferroic nanocomposites to overcome inherent shortcomings for conventional layered (e.g. clamping effect) and vertically aligned (e.g. leaky) films are instrumental to realize genuine multiferroic behaviors. Here the self-assembled architecture with three-dimensional (3D) framework of heterostructures is fabricated, wherein well-ordered multiferroic ε-Fe2O3 (ε-FO) nanoboats are embedded in a ferroelectric perovskite PbTiO3 (PTO) matrix. The biphasic system combines strong interfacial magnetoelectric couplings of vertically aligned heterostructure and addressed leakage issue via preferential epitaxy of a high-resistance transition layer of PTO. Additionally, the two phases maintain full lattice coherence along vertical interfaces allowing for efficient interfacial strain coupling. Ferroelectricity and piezoelectric switching of the 3D nanostructured PTO:ε-FO film have been corroborated macroscopically by polarization hysteresis (Ps ~ 45 μC cm−2) and locally by piezoresponse force microscopy, and strong magnetoelectric coupling has been manifested as a sizable modification of piezoelectric switching characteristics via applying a DC magnetic field, all conducting at room temperature. The novel 3D multiferroic-ferroelectric heterostructure offers great potential for nanoengineering of multiferroic composites, thus opens an avenue towards superior microelectronics and spintronics.

Electrical tuning of skyrmion dynamics in multiferroic composite thin films

A lack of space-inversion symmetry along with broken time-reversal symmetry at ferromagnetic/ferroelectric interfaces gives rise to the electric field control of the effective magnetic field and the Dzyaloshinskii-Moriya interaction, thus allowing for the formation of multiferroic skyrmions at room temperature. The electric-field-driven evolution of spin textures at the ferromagnetic/ferroelectric interface is investigated by means of Monte Carlo simulations. It is demonstrated that the skyrmion lattice can be stabilized by the moderate interfacial magnetoelectric couplings. The chirality, radius, position, and numbers of skyrmions are found to be tunable by an external the electric field. The nonequilibrium dynamics of skyrmions, however, strongly depends on the frequency of the applied time-oscillating electric field. With the increase of the frequency of the ac electric field, multiferroic skyrmions become unstable and after several periods they are, ultimately, damping down to the helimagnetic phase. Under microwavelike electric fields, the dynamic multiferroic response of the skyrmion lattice is anisotropic and inhomogeneous. The electric-field-induced resonance spectrum of the magnetic skyrmion with a distinct peak in the imaginary part of permeability is successfully simulated by the Fourier transformation of magnetization.

Interfacial Effect Enhanced Electric Field Control of the Magnetism in Pt/Fe/PMN-PT Heterostructures

The strain and charge comediated magnetoelectric coupling effect has been investigated in the Pt/Fe/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) heterostructures. An oxidized interfacial layer FeOx is formed at the Fe/PMN-PT interface, which assists in realizing the multistate magnetization by the electric field. The remnant magnetization variation under the positive polarization reaches ∼120% in the (011) Pt/Fe(2 nm)/PMN-PT heterostructure along the in-plane [01–1] direction, which is larger than that (∼67% and ∼1.8%) of the Pt/Fe/PMN-PT heterostructures with 5 and 11 nm Fe films. The enhanced electric field manipulation of magnetization variation as the thickness of the Fe film decreases indicates an interfacial dominant magnetoelectric coupling effect. Moreover, the asymmetrical magnetization variation under the positive and negative electric fields originates from the ferroelectric polarization induced carrier density change and redox–oxidation reactions based on the strain effect at the interfacial FeOx la...

Magnon-driven interfacial magnetoelectric coupling in Co/PMN-PT multiferroic heterostructures.

Magnon-driven interfacial magnetoelectric coupling in Co/PMN-PT multiferroic heterostructures is investigated at room temperature. The electric field controlled ferromagnetic resonance field possesses a loop-like curve, with a large resonance field shift between positive and negative remanent polarizations, which confirms a non-volatile strong magnetoelectric coupling. However, with a non-magnetic Ta layer inserted at the Co/PMN-PT interface, a piezostrain-induced butterfly-like curve of the resonance field versus applied electric field of the Co/Ta/PMN-PT multiferroic heterostructure is observed. Further, the non-volatile behavior of the resonance field changing with the applied electric field can be obtained, consistent with the result of polarization versus applied electric field curve, which can be attributed to the magnon-driven interfacial magnetoelectric coupling, showing a strong correlation of magnetization of Co thin film and the polarization of PMN-PT. The result is promising for the design of future multiferroic devices.

Distinguishing charge and strain coupling in ultrathin (001)-La0.7Sr0.3MnO3/PMN-PT heterostructures

Interfacial charge and strain distributions inside artificial perovskite ABO3 heterostructures often affect intriguing physical properties that are important to device performance. Normally, both charge and strain coexist across the interfaces, and their exact roles in determining the properties remain elusive. In the present work, La0.7Sr0.3MnO3 (LSMO) ultrathin films were grown on (001)-0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMNPT) single-crystal substrates to discriminate between the effect of charge and strain on the transport and magnetoelectric properties. In heterostructures with thicker LSMO films, the strain effect dominates the resistance and the magnetic moment depends on the external electric field. With the decreasing LSMO thickness, the butterfly-like resistance–electric-field (R-E) and magnetization–electric-field (M-E) curves become loop-like, indicating that charge effects dominate strain effects in determining the electric field that controls the transport and magnetic properties. Furthermore, soft-x-ray absorption spectra of 32 and 4 nm LSMO/PMNPT samples at the Mn L edge under an applied electric field of ±6 kV/cm indicate that orbital reconstruction also plays an important role in interfacial magnetoelectric coupling.

Improving Magnetoelectric Contactless Sensing and Actuation through Anisotropic Nanostructures

Flexible polymer-based magnetoelectric (ME) materials are developed based on novel CoFe2O4(CoFO) nanoellipsoids and poly[vinylidenefluoride-co-trifluoroethylene] [P(VDF-TrFE)]. The synthesized noncytotoxic CoFO nanoellipsoids (270 nm × 50 nm) show high magnetization, ≈170 emu·g–1, high magnetostriction, ≈300 ppm, and magnetic anisotropy that, coupled to the piezoelectric response of P(VDF-TrFE), |d33| = 21 ± 1 pC·N–1, lead to an interfacial ME coupling (α) of 1.50 mV·cm–1·Oe–1. Further, nanoellipsoid orientation within the polymer matrix allows an anisotropic ME response of the CoFO/P(VDF-TrFE) composite. Such a response is dependent on the angle between the dc magnetic field direction and the nanoellipsoids length direction. The proposed mechanism for the anisotropic behavior allows the tailoring of the ME response to contactless sensing applications.

Magnetic field-directed hybrid anisotropic nanocomposites

A facile bottom-up approach is developed to grow magnetic metallic Cu/FeCo (core/shell) nanowires, where their distribution and orientation can be controlled by magnetic field. The nanocomposites consisting of a ferroelectric polymer matrix and magnetic nanowire arrays exhibit the orientation-controlled anisotropy and interfacial magnetoelectric coupling effect.

The magnetic properties of CoFeB and CoFeB/Ag nanodot arrays fabricated by a template transfer imprinting method

In this study, a practical method for fabricating size-tunable and periodic CoFeB and CoFeB/Ag nanodot arrays on glass substrate was developed using a template transfer imprinting method, which consisted of nanoimprint lithography and vacuum magnetron sputtering. It was found that the coercivity could be distinctly enhanced by introducing periodic CoFeB nanodot arrays. Also, the coercivity of the CoFeB/Ag nanodot arrays could be flexibly tuned over a wide range by tailoring the thickness of the Ag layer, due to the interfacial magneto-electric coupling effect. Investigations such as those conducted in this study will provide promising references for the future fabrications of high performance nanostructured magnetic materials, which can be potentially utilized in many fields.

Ferroelectric domain switching dynamics and memristive behaviors in BiFeO3-based magnetoelectric heterojunctions

The ferroelectric domain reversal dynamics and the corresponding resistance switching as well as the memristive behaviors in epitaxial BiFeO3 (BFO, ~150 nm) based multiferroic heterojunctions were systematically investigated. The ferroelectric domain reversal dynamics could be described by the nucleation-limited-switching model with the Lorentzian distribution of logarithmic domain-switching times. By engineering the domain states, multi and even continuously tunable resistances states, i.e. memristive states, could be non-volatilely achieved. The resistance switching speed can be as fast as 30 ns in the BFO-based multiferroic heterojunctions with a write voltage of ~20 V. By reducing the thickness of BFO, the La0.6Sr0.4MnO3/BFO (~5 nm)/La0.6Sr0.4MnO3 multiferroic tunnel junction (MFTJ) shows an even a quicker switching speed (20 ns) with a much lower operation voltage (~4 V). Importantly, the MFTJ exhibits a tunable interfacial magnetoelectric coupling related to the ferroelectric domain switching dynamics. These findings enrich the potential applications of multiferroic BFO based devices in high-speed, low-power, and high-density memories as well as future neuromorphic computational architectures.

Gate-controlled magnon-assisted switching of magnetization in ferroelectric/ferromagnetic junctions

Interfacing a ferromagnet with a polarized ferroelectric gate generates a non-uniform, interfacial spin density coupled to the ferroelectric polarization allowing so for an electric field control of effective transversal field to magnetization. Here we study the dynamic magnetization switching behavior of such a multilayer system based on the Landau-Lifshitz-Baryakhtar equation, demonstrating that interfacial magnetoelectric coupling is utilizable as a highly localized and efficient tool for manipulating magnetism.

Self-Poling-Induced Magnetoelectric Effect in Highly Strained Epitaxial BiFeO3/La0.67Sr0.33MnO3-δ Multiferroic Heterostructures.

Highly strained epitaxial BiFeO3/La0.67Sr0.33MnO3-δ (BFO/LSMO) heterostructures were fabricated on LaAlO3 substrates by magnetron sputtering. The as-grown downward self-polarization of BFO capping layers was confirmed by piezoelectric force microscopy. Using the electrostatic field-induced charge screening, a hole depletion state was induced in ultrathin (8 nm) LSMO films. As a result of the interfacial charge coupling, appreciable saturated magnetization (MS) increase of about 500 and 100% can be observed in LSMO with BFO capping at 5 and 300 K, respectively. Besides, LSMO phase translations can be revealed by the BFO thickness-related exchange bias field (HE) and MS of the BFO/LSMO heterostructures. The results established a new approach in achieving interfacial magnetoelectric couplings with thin self-polarized multiferroic layers.

Quantitative Determination on Ionic-Liquid-Gating Control of Interfacial Magnetism.

Ionic-liquid gating on a functional thin film with a low voltage has drawn a lot of attention due to rich chemical, electronic, and magnetic phenomena at the interface. Here, a key challenge in quantitative determination of voltage-controlled magnetic anisotropy (VCMA) in Au/[DEME]+ [TFSI]- /Co field-effect transistor heterostructures is addressed. The magnetic anisotropy change as response to the gating voltage is precisely detected by in situ electron spin resonance measurements. A reversible change of magnetic anisotropy up to 219 Oe is achieved with a low gating voltage of 1.5 V at room temperature, corresponding to a record high VCMA coefficient of ≈146 Oe V-1 . Two gating effects, the electrostatic doping and electrochemical reaction, are distinguished at various gating voltage regions, as confirmed by X-ray photoelectron spectroscopy and atomic force microscopy experiments. This work shows a unique ionic-liquid-gating system for strong interfacial magnetoelectric coupling with many practical advantages, paving the way toward ion-liquid-gating spintronic/electronic devices.

Strain-controlled interfacial magnetization and orbital splitting in La2/3Sr1/3MnO3/tetragonal BiFeO3 heterostructures

The electronic and magnetic properties of La2/3Sr1/3MnO3(LSMO)/tetragonal BiFeO3(BFO) heterostructures with the xy-plane biaxial strain were investigated by first-principles calculations. As the xy-plane lattice constant is ranging from 3.619 to 3.921 Å, a large interfacial magnetoelectric coupling (IMEC) appears in the LaO/Fe-O2 and LaO/O2-Fe models. Particularly, the interfacial Mn in the LaO/O2-Fe model shows a large spin-down t2g orbital splitting at a strain from −2% to 6%, where the maximum splitting energy is 283 meV at 2%. Additionally, the LaO/O2-Fe model is half-metallic at a strain of 2%, 4%, and 6%. The results demonstrate that IMEC, orbital occupancy, and half-metallicity of LSMO/BFO heterostructures can be effectively engineered by the interfacial coupling and in-plane strain, which paves a way for designing the novel magnetoelectric devices.

Inversion of Ferrimagnetic Magnetization by Ferroelectric Switching via a Novel Magnetoelectric Coupling.

Although several multiferroic materials or heterostructures have been extensively studied, finding strong magnetoelectric couplings for the electric field control of the magnetization remains challenging. Here, a novel interfacial magnetoelectric coupling based on three components (ferroelectric dipole, magnetic moment, and antiferromagnetic order) is analytically formulated. As an extension of carrier-mediated magnetoelectricity, the new coupling is shown to induce an electric-magnetic hysteresis loop. Realizations employing BiFeO_{3} bilayers grown along the [111] axis are proposed. Without involving magnetic phase transitions, the magnetization orientation can be switched by the carrier modulation driven by the field effect, as confirmed using first-principles calculations.