Strong Magnetoelectric Coupling Research Articles

Exploring the Structural, Morphological, and Multiferroic Properties of Al3+ Modified (1-x)BCZT-(x)CFO Ceramic Composites

Abstract Multiferroics with strong magnetoelectric coupling can be created by improving the magnetostriction of the ferrite phase and combining it with the best known piezoelectric. Herein, the ferromagnetic CoFe2O4 was modified with Al3+ ions (CAF) to further improve the resistivity, magnetic, and magnetostrictive properties and then combined with (0.5)Ba(Zr0.2Ti0.8)O3−(0.5)(Ba0.7Ca0.3)TiO3(BCZT) with different weight percentages. XRD results revealed the presence of a mixed spinel cubic phase for CAF (Fd-3m), whereas BCZT crystallized in a tetragonal structure (Amm2) in composite systems. Composites exhibited well-developed hysteresis loops with no feature of leakage current and dielectric response was consistent with ferroelectric properties. The magnetic response of CAF sample improved significantly which is attributed to preference of Al3+ ions on tetrahedral sites. The magnetization of composites increased as the nonmagnetic BCZT component increased and (0.75)CAF-(0.25)BCZT system had the highest saturation magnetization. We anticipate that these systems will have significantly improved magnetoelectric characteristics than unmodified CF-BCZT system.

Two-Dimensional Os2Se3 Nanosheet: A Ferroelectric Metal with Room-Temperature Ferromagnetism.

Two-dimensional (2D) ferroelectric metals (FEMs) possess intriguing characteristics, such as unconventional superconductivity and the nonlinear anomalous Hall effect. However, their occurrence is exceedingly rare due to mutual repulsion between ferroelectricity and metallicity. In addition, further incorporating other features like ferromagnetism into FEMs to enhance their functionalities poses a significantly greater challenge. Here, via first-principles calculations, we demonstrate a case of an FEM that features a coexistence of room-temperature ferromagnetism, ferroelectricity, and metallicity in a thermodynamically stable 2D Os2Se3. It presents a vertical electric polarization of 3.00 pC/m that exceeds those of most FEMs and a moderate polarization switching barrier of 0.22 eV per formula unit. Moreover, 2D Os2Se3 exhibits robust ferromagnetism (Curie temperature TC ≈ 527 K) and a sizable magnetic anisotropy energy (-30.87 meV per formula unit). Furthermore, highly magnetization-dependent electrical conductivity is revealed, indicative of strong magnetoelectric coupling. Berry curvature calculation suggests that the FEM might exhibit nontrivial band topology.

First-principles study on the p-orbital multiferroicity of single-layer XN (X = Ge, Sn, Pb)

Two-dimensional (2D) multiferroic materials have triggered a burst of interest owing to their wide applications in nanoelectronics. Specifically, p-orbital multiferroicity is strongly desired but has been very few reported. Here, based on first-principles calculations, we unveil a new type of 2D multiferroic material: the single-layer (SL) XN (X = Ge, Sn, Pb). Our findings show these materials are ferromagnetic semiconductors with strong magnetoelectric coupling and wide bandgaps. The multiferroicity is related to the unpaired p-orbital electrons of N atoms and the buckled crystal structure. All the single layers show easy-plane magnetocrystalline anisotropy, and the magnetic anisotropy energy increases significantly with the atomic number increasing. Our Monte Carlo simulations suggest the Curie temperature TC is 205.44 K, 200.45 K, and 287.88 K for SL GeN, SnN, and PbN, respectively. By applying tensile strain, the TC can be further increased to 225.39 K, 245.35 K, 369.99 K, respectively. Additionally, biaxial strain can induce semiconductor-to-half-metal and ferroelectricity-to-paraelectricity transition in the single layers. We aspire that our work contributes to the exploration of room-temperature p-orbital multiferroicity.

Single or Vortex Ferroelectric and Ferromagnetic Domain Nanodot Array of Magnetoelectric BiFe0.9Co0.1O3.

Nanodots composed of multiferroic cobalt-substituted BiFeO3, a ferroelectric ferromagnet at room temperature, are fabricated by pulsed laser deposition using anodized porous alumina as masks. The obtained nanodots are approximately 60 nm in diameter, more than 10 nm in thickness, and approximately 70 Gbit/in.2 in density. Piezoresponse and magnetic force microscopies show both ferroelectricity and ferromagnetism with a single-domain nature. It is also found that the dot with 190 nm diameter had multidomain vortex ferroelectric and magnetic structures indicating the strong magnetoelectric coupling. The single-domain cobalt-substituted BiFeO3 nanodots are suitable for verifying magnetization reversal by the electric field, which is the first step in the development of low-power-consumption nonvolatile magnetic memory devices.

First-Principles Study on Evolution of Magnetic Domain in Two-Dimensional BaTiO3 Ultrathin Film Doped with Co under Electric Field.

The magnetization mechanism of Co-doped BaTiO3 ultrathin films is a subject of debate, which results in difficulties with the design of new multiferroics based on BaTiO3 matrixes. With the aid of a first-principles approach, it was observed that when the interstitial site and Ti vacancy were filled with Co, the configuration behaved in a nonmagnetic manner, indicating the significance of the Co content. Moreover, in the case of Co substituting two neighboring Ti atoms, when a direct current field was applied in the [100] direction, the magnetic domains excluding those in the [100], [010], and [001] directions were directed away. Further, the magnetoelectric constant was evaluated at ~449.3 mV/cmOe, showing strong magnetoelectric coupling at room temperature. Clearly, our study indicates that strict control of Ba, Ti, O, and Co stoichiometry can induce an electric and magnetic field conversion in two-dimensional BaTiO3 and may provide a new candidate for single-phase multiferroics for application in next-generation multifunctional devices.

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.

Ptychographic Nanoscale Imaging of the Magnetoelectric Coupling in Freestanding BiFeO3.

Understanding the magnetic and ferroelectric ordering of magnetoelectric multiferroic materials at the nanoscale necessitates a versatile imaging method with high spatial resolution. Here, soft X-ray ptychography is employed to simultaneously image the ferroelectric and antiferromagnetic domains in an 80nm thin freestanding film of the room-temperature multiferroic BiFeO3 (BFO). The antiferromagnetic spin cycloid of period 64nm is resolved by reconstructing the corresponding resonant elastic X-ray scattering in real space and visualized together with mosaic-like ferroelectric domains in a linear dichroic contrast image at the Fe L3 edge. The measurements reveal a near perfect coupling between the antiferromagnetic and ferroelectric ordering by which the propagation direction of the spin cycloid is locked orthogonally to the ferroelectric polarization. In addition, the study evinces both a preference for in-plane propagation of the spin cycloid and changes of the ferroelectric polarization by 71°between multiferroic domains in the epitaxial strain-free, freestanding BFO film. The results provide a direct visualization of the strong magnetoelectric coupling in BFO and of its fine multiferroic domain structure, emphasizing the potential of ptychographic imaging for the study of multiferroics and non-collinear magnetic materials with softX-rays.

Non-volatile voltage-controlled magnetization in single-phase multiferroic ceramics at room temperature

Single-phase multiferroics (MFs) exhibiting ferroelectricity and ferromagnetism and the strong magnetoelectric (ME) coupling effect at room temperature are seen as key to the development of the next-generation of spintronic devices, multi-state memories, logic devices and sensors. Herein, the single-tetragonal phase (1–x) (Sr0·3Bi0·35Na0·329Li0.021)TiO3-xBiFeO3 (x = 0.2 or 0.4) system was designed to study the intrinsic ME coupling effect at room temperature and high frequencies. The polarization arises from the cooperative displacement of both Fe3+ and Ti4+ relative to the oxygen sublattice in the tetragonally distorted perovskite structure, and the magnetization stems from indirect exchange magnetic interaction between adjacent iron ions. A switchable voltage-controlled magnetization was confirmed by a change of the coercive magnetic field, Hc, and remnant magnetization, Mr, in the x = 0.4 component subjected to an external electric field at room temperature and was possibly attributed to a strain-mediated ME coupling effect. In addition, resonance behaviours of the complex magnetic permeability and complex dielectric permittivity in the GHz band indicate that this ME effect is intrinsic in nature and could broaden the applications of multiferroics to devices operating at microwave frequencies.

Spin-Chirality-Driven Multiferroicity in van der Waals Monolayers.

Driven by the expected contribution of two-dimensional multiferroic systems with strong magnetoelectric coupling to the development of multifunctional nanodevices, here we propose, by means of first-principles calculations, vanadium-halide monolayers as a new class of spin-chirality-driven van der Waals multiferroics. The frustrated 120-deg magnetic structure in the triangular lattice induces a ferroelectric polarization perpendicular to the spin-spiral plane, whose sign is switched by a spin-chirality change. It follows that, in the presence of an applied electric field perpendicular to the monolayers, one magnetic chirality can be stabilized over the other, thereby allowing the long-sought electrical control of spin textures. Moreover, we demonstrate the remarkable role of spin-lattice coupling on magnetoelectricity, which adds to the expected contribution of spin-orbit interaction determined by an anion. Indeed, such compounds exhibit sizeable spin-driven structural distortions, thereby promoting the investigation of multifunctional spin-electric-lattice couplings.

Two-Dimensional Asymmetric Multiferroics: Unique Way toward Strong Magnetoelectric Coupling and Multistate Memory.

Two-dimensional (2D) materials have provided a fascinating platform for exploring novel multiferroics and emergent magnetoelectric coupling mechanisms. Here, a novel 2D asymmetric multiferroic based on Janus 2D multiferroic MXene-analogous oxynitrides (InTlNO2) is presented by using first-principles calculations. We find three inequivalent phases for InTlNO2, including two metallic phases (p1 and p2) and one semiconducting phase (p3) with a band gap of 0.88 eV. All phases are room-temperature multiferroics with different Curie temperatures, leading to tunability by phase transitions. We show that there is a 90° rotation of the magnetic anisotropy easy axis between p1 and p2, where p1 favors the in-plane and p2 the out-of-plane easy axis. Therefore, the magnetic anisotropy can be tuned by reversing the out-of-plane polarization. Our strategy provides a unique way toward strong magnetoelectric coupling and multistate memory.

Epitaxial Stabilization and Persistent Nucleation of the 3C Polymorph of Ba0.6Sr0.4MnO3.

Ba-rich compositions in the BaxSr1-xMnO3 (BSMO) cubic perovskite (3C) system are magnetic ferroelectrics and are of interest for their strong magnetoelectric coupling. Beyond x = 0.5, they only form in hexagonal polymorphs. Here, the 3C phase boundary is pushed to Ba0.6Sr0.4MnO3 for the thin films. Using regular pulsed laser deposition (rPLD), 3C Ba0.6Sr0.4MnO3 could be epitaxially stabilized on DyScO3 (101)o substrates by using a 0.1% O2/99.9% N2 gas mixture. However, the 3C phase was mixed with the 4H polymorph for films 24 nm thick and above, and the films were relatively rough. To improve flatness and phase purity, changes in growth kinetics were investigated and interval PLD (iPLD) was especially effective. In iPLD, deposition is interrupted after completion of approximately one monolayer, and the deposit is annealed for a specific period of time before repeating. Both film flatness and, more importantly, the volume of the 3C polymorph improved with iPLD, resulting in 40 nm single-phase films. The results imply that iPLD improves the persistent nucleation of highly metastable phases and offers a new approach to epitaxial stabilization of novel materials, including more Ba-rich BSMO compositions in the 3C structure.

Emergent ultrasmall multiferroics in paraelectric perovskite oxide by hole polarons.

Ultimately small multiferroics with coupled ferroelectric and ferromagnetic order parameters have drawn considerable attention for their tremendous technological potential. Nevertheless, these ferroic orders inevitably disappear below the critical size of several nanometers in conventional ferroelectrics or multiferroics. Here, based on first-principles calculations, we propose a new strategy to overcome this limitation and create ultrasmall multiferroic elements in otherwise nonferroelectric CaTiO3 by engineering the interplay of oxygen octahedral rotations and hole polarons, though both of them are generally believed to be detrimental to ferroelectricity. It is found that the hole doped in CaTiO3 spontaneously forms a localized polaronic state. The lattice distortions associated with a hole polaron interacting with the intrinsic oxygen octahedral rotations in CaTiO3 effectively break the inversion symmetry and create atomic-scale ferroelectricity beyond the critical size limitation. The hole polaron also causes highly localized magnetism attributed to the associated spin-polarized electric state and thus manifests as a multiferroic polaron. Moreover, the hole polaron exhibits high hopping mobility accompanied by rich switching of polarization and magnetic directions, indicating strong magnetoelectric coupling with a mechanism dissimilar from that of conventional multiferroics. The present work provides a new mechanism to engineer inversion symmetry and opens avenues for designing unusual multifunctional materials.

Magneto-electric coupling beyond van der Waals interaction in two-dimensional multiferroic heterostructures

Exploring two-dimensional (2D) multiferroic systems with strong magneto-electric coupling properties holds significant application value in nanoscale spintronics devices. However, due to the weak interlayer van der Waals interactions, strong magneto-electric coupling in 2D heterostructures is relatively rare. By using first-principles simulations, we demonstrate that in the NiPS3/Sc2CO2 heterostructure, the ferroelectric polarization switching of the Sc2CO2 layer induces a transition in the magnetic ground state of the NiPS3 layer from the ferromagnetic state to antiferromagnetic ordering, accompanied by a transformation from a semiconductor to a half-metallic state. This magnetic phase transition is caused by a novel magneto-electric coupling mechanism: the polarization switching changes the band alignment between the two materials and then induces a significant interlayer charge transfer, leading to the emergence of Stoner itinerant ferromagnetism. In addition, the polarization switching can also change the magnetic anisotropy from an easy magnetization plane to an easy magnetization axis. These results not only offer a promising multiferroic heterostructure for nonvolatile memory devices and magnetic sensors but also provide a feasible approach for designing multiferroic system with strong magneto-electric coupling.

Out-of-plane ferroelectricity and robust magnetoelectricity in quasi-two-dimensional materials.

Thin-film ferroelectrics have been pursued for capacitive and nonvolatile memory devices. They rely on polarizations that are oriented in an out-of-plane direction to facilitate integration and addressability with complementary metal-oxide semiconductor architectures. The internal depolarization field, however, formed by surface charges can suppress the out-of-plane polarization in ultrathin ferroelectric films that could otherwise exhibit lower coercive fields and operate with lower power. Here, we unveil stabilization of a polar longitudinal optical (LO) mode in the n = 2 Ruddlesden-Popper family that produces out-of-plane ferroelectricity, persists under open-circuit boundary conditions, and is distinct from hyperferroelectricity. Our first-principles calculations show the stabilization of the LO mode is ubiquitous in chalcogenides and halides and relies on anharmonic trilinear mode coupling. We further show that the out-of-plane ferroelectricity can be predicted with a crystallographic tolerance factor, and we use these insights to design a room-temperature multiferroic with strong magnetoelectric coupling suitable for magneto-electric spin-orbit transistors.

First-principles investigation of the magnetoelectric properties of Ba7Mn4O15

Type-II multiferroics, in which the magnetic order breaks inversion symmetry, are appealing for both fundamental and applied research due their intrinsic coupling between magnetic and electrical orders. Using first-principles calculations we study the ground state magnetic behaviour of Ba7Mn4O15 which has been classified as a type-II multiferroic in recent experiments. Our constrained moment calculations with the proposed experimental magnetic structure shows the spontaneous emergence of a polar mode giving rise to an electrical polarisation comparable to other known type-II multiferroics. When the constraints on the magnetic moments are removed, the spins self-consistently relax into a canted antiferromagnetic ground state configuration where two magnetic modes transforming as distinct irreducible representations coexist. While the dominant magnetic mode matches well with the previous experimental observations, the second mode is found to possess a different character resulting in a non-polar ground state. Interestingly, the non-polar magnetic ground state exhibits a significantly strong linear magnetoelectric (ME) coupling comparable to the well-known multiferroic BiFeO3, suggesting strategies to design new linear MEs.

CO2 -Induced Spin-Lattice Coupling for Strong Magnetoelectric Materials.

The preparation of 2D magnetoelectric (ME) nanomaterials with strong ME coupling is crucial for the fast reading and writing processes in the next generation of storage devices. Herein, 2D BaTiO3 (BTO)-CoFe2 O4 (CFO) ME nanocomposites are prepared through a substrate-free coupling strategy using supercritical CO2 . Such 2D BTO-CFO with strong coupling is built through alternating in-plane and out-of-plane epitaxy stacking, leading to remarkable mutual biaxial strain effects for spin-lattice coupling. As a results, such strain effect significantly enhances the ferroelectricity of BTO and the ferrimagnetism of CFO, where an unexceptionally high ME coupling coefficient of (325.8mVcm-1 Oe-1 ) is obtained for the BTO-CFO nanocomposites.

Linear magnetoelectric coupling and type-II multiferroic order in NiMn2O4

We report an unexplored type-II multiferroic order in NiMn2O4, exhibiting strong linear magnetoelectric coupling above liquid-nitrogen (LN) temperature. The compound becomes ferroelectric at ∼100 K, coinciding with ferrimagnetic ordering, with a polarization value of ∼535 μC/m2 for a poling field of 5 kV/cm. At LN temperature, the polarization value increases linearly (∼21%) with a magnetic field up to 30 kOe. Rietveld refinement of neutron diffraction patterns reveals a ferrimagnetic model with antiparallel moments at tetrahedral and octahedral sites, as well as a canting of octahedral moment persisting up to ∼100 K. Low-temperature synchrotron diffraction confirms a step-like oxygen displacement during multiferroic ordering, suggesting that the Dzyaloshinskii–Moriya interaction polarizes the intervening oxygen atoms through magnetostriction, providing a microscopic mechanism for spontaneous electric polarization in this linear magnetoelectric multiferroic compound.

Improvement of leakage, magnetic and magnetodielectric properties in cobalt doped gallium ferrite

Gallium ferrite (GFO) is a magnetoelectric (ME) material, capturing growing attention due to its strong ME coupling at room temperature. However, the application of the material in practical use is hindered due to its high leakage. In this work, the effects of cobalt (Co) substitution at the iron (Fe) sites of GaFe1−x Co x O3 (0.0 ⩽ x ⩽ 0.1) polycrystals on the structure, electric and magnetic properties are investigated in detail. 5 at. wt.% substitution (x = 0.05) with cobalt ions achieves a reduction in leakage current density by four orders of magnitude due to reduced hopping between Fe3+ and Fe2+ ions and suppression of the oxygen vacancy formation. This is supported by higher dielectric constant and lower dielectric loss, as well as a significant difference between grain and grain boundary resistances. Two-phase-like magnetic behavior in magnetic hysteresis loop with enhanced magnetization and two magnetic transition temperatures are observed in the doped samples. All samples exhibited an increase in the magnetodielectric factor, indicating enhanced coupling between magnetic and electrical parameters. By concurrently increasing dielectric, magnetic, and coupling between them, this study describes a viable technique for lowering the most significant impediment to GFO’s usage as a ME device.

Application of the Lock-In Technique in Magnetoelectric Coupling Measurements of the PZT/Terfenol-D Composite

This paper presents a study of magnetoelectric (ME) properties of the PZT/Terfenol-D composite with a varying number of layers. The composite consists of piezoelectric and magnetostrictive phases that are mechanically coupled. The purpose of this setup is to gain control over the electric polarization of a material via an external magnetic field. Unlike most similar composites, our samples utilize a commercial piezoelectric patch instead of pure PZT. At present, researchers face two main problems regarding magnetoelectric materials: (i) the effect is observed far below room temperature for single-phase materials, and (ii) the ME coupling is too weak to be commercially viable. Our research was carried out via the lock-in technique on two PZT/Terfenol-D samples we synthesized. Relatively strong room-temperature magnetoelectric coupling between piezoelectric and magnetostrictive phases was observed for both samples. Two types of characteristics were investigated: (i) ME voltage versus magnetic AC field frequency, and (ii) ME voltage versus magnetic DC field. We detected multiple, grouped signal peaks ascribed to different resonance modes. Uniquely, the peaks form band-like characteristics which might be an important step in bringing the materials closer to wider commercial use.

Optical and magnetoelectric coupling studies of ErCrO3

ErCrO3 samples were synthesized by solid state method. The structure, optical, magnetic, dielectric and low-temperature pyroelectric properties of the system were investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that the sample has an orthorhombic structure with the Pbnm space group, and an average particle size of 641 nm. Optical studies show that the optical band gaps are 2.1 eV and 3.2 eV for the sample. DC and AC magnetization indicate that ErCrO3 undergoes three magnetic phase transitions near TN (Cr3+), TSR, and TN(Er3+). Interestingly, another hump is observed in the range of 50–70 K during the AC magnetization measurements. Dielectric and pyroelectric measurements demonstrate significant anomalies in the dielectric permittivity and pyroelectricity around TN, TSR and the corresponding temperature of the hump. This suggests a close correlation between the dielectric and pyroelectric properties with the magnetic transition. Furthermore, the pyroelectric measurements at low temperatures prove that the magnetic field could regulate the electric polarization, a further proof of the strong magnetoelectric coupling effect in the system. These properties of ErCrO3 make it have significant applications in optoelectronic devices, storage devices, sensors, and so on.