Large Magnetoelectric Coupling Research Articles

Substrate clamping effect onto magnetoelectric coupling in multiferroic BaTiO3-CoFe2O4 core-shell nanofibers via coaxial electrospinning

We report large lateral magnetoelectric (ME) coupling coefficients α31 of and in substrate bonded and free-standing multiferroic BaTiO3-CoFe2O4 (BTO-CFO) core-shell nanofibers (NFs) with and without substrate clamping effect, respectively. The BTO-CFO core-shell NFs were synthesised by a sol-gel coaxial electrospinning technique, and their ME coupling was directly observed by demonstrating the evolution of piezoelectric coefficient (d33), ferroelectric domain, and phase contrast induced by an external magnetic field. These impressed α31 coefficients originated from the nanoconfinement of the interphase elastic interaction between the ferromagnetic core fiber and the ferroelectric shell interlayer, as well as the strain transformation at the one-dimensional (1D) fiber boundary. This means that the decreasing substrate clamping effect results in an enhanced ME coupling in multiferroic NFs, which is similar to that of thin films. These findings make people understand the substrate clamping effect and enable nanoscale ME device applications.

Giant magnetoelectric coupling interaction in BaTiO3/BiFeO3/BaTiO3 trilayer multiferroic heterostructures

Multiferroic trilayer thin films of BaTiO3/BiFeO3/BaTiO3 were prepared by RF-magnetron sputtering technique at different thicknesses of BiFeO3 layer. A pure phase polycrystalline growth of thin films was confirmed from X-ray diffraction results. The film showed maximum remnant electric polarization (2Pr) of 13.5 μC/cm2 and saturation magnetization (Ms) of 61 emu/cc at room temperature. Thermally activated charge transport dominated via oxygen vacancies as calculated by their activation energy, which was consistent with current–voltage characteristics. Magnetic field induced large change in resistance and capacitance of grain, and grain boundary was modeled by combined impedance and modulus spectroscopy in the presence of varied magnetic fields. Presence of large intrinsic magnetoelectric coupling was established by a maximum 20% increase in grain capacitance (Cg) with applied magnetic field (2 kG) on trilayer having 20 nm BiFeO3 layer. Substantially higher magnetoelectric coupling in thinner films has been observed due to bonding between Fe and Ti atoms at interface via oxygen atoms. Room temperature magnetoelectric coupling was confirmed by dynamic magnetoelectric coupling, and maximum longitudinal magnetoelectric coupling of 515 mV/cm-Oe was observed at 20 nm thickness of BiFeO3. The observed magnetoelectric properties are potentially useful for novel room temperature magnetoelectric and spintronic device applications for obtaining higher voltage at lower applied magnetic field.

Manipulating pseudospin-polarized state of light in dispersion-immune photonic topological metacrystals

We proposed a group-theory method to calculate topological invariant in bi-isotropic photonic crystals invariant under crystallographic point group symmetries. Spin Chern number has been evaluated by the eigenvalues of rotation operators at high symmetry k-points after the pseudo-spin polarized fields are retrieved. Topological characters of photonic edge states and photonic band gaps can be well predicted by total spin Chern number. Nontrivial phase transition is found in large magnetoelectric coupling due to the jump of total spin Chern number. Light transport is also issued at the {\epsilon}/{\mu} mismatching boundary between air and the bi-isotropic photonic crystal. This finding presents the relationship between group symmetry and photonic topological systems, which enables the design of photonic nontrivial states in a rational manner.

Self-Biased Magnetoelectric Composites: An Overview and Future Perspectives

Abstract Self-biased magnetoelectric (ME) composites, defined as materials that enable large ME coupling under external AC magnetic field in the absence of DC magnetic field, are an interesting, challenging and practical field of research. In comparison to the conventional ME composites, eliminating the need of DC magnetic bias provides great potential towards device miniaturization and development of components for electronics and medical applications. In this review, the current state-of-the-art of the different self-biased structures, their working mechanisms, as well as their main characteristics are summarized. Further, the nature and requirement of the self-biased magnetoelectric response is discussed with respect to the specific applications. Lastly, the remaining challenges as well as future perspective of this research field are discussed.

Magneto-electric coupling in Ca3CoMnO6 thin films

We report on the growth and magneto-electric (ME) coupling of Ca3CoMnO6 thin films deposited by pulsed laser deposition technique. Ca3CoMnO6 is interesting because of its tunable inter-chain magnetic interactions that affect its ME coupling. An optical band gap of 1.73eV was estimated by UV visible spectroscopy. The magnetic transition is surprisingly increased to 40K, much above its bulk value (15K). The increase in magnetic transition temperature is possibly due to stronger inter-chain interaction and strain caused by lattice mismatch. Due to canting the thin films show weak ferromagnetic like behavior at low temperature. The dielectric measurements show anomaly at 10K and 40K which are clearly visible at the first derivative of dielectric data. From direct polarization measurements we associate the 10K transition to a magnetic structure driven ferroelectric phase. The magnetocapacitance data at 5K shows substantial change in dielectric constant with magnetic field. The large ME coupling is also verified by polarization measurement, where a 5% change in polarization is observed on the application of 5T external magnetic field.

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.

Electric field mediated non-volatile tuning magnetism at the single-crystalline Fe/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 interface.

We report non-volatile electric-field control of magnetism modulation in Fe/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) heterostructure by fabricating an epitaxial Fe layer on a PMN-PT substrate using a molecular beam epitaxy technique. The remnant magnetization with a different electric field shows a non-symmetric loop-like shape, which demonstrates a change of interfacial chemistry and a large magnetoelectric coupling in Fe/PMN-PT at room temperature to realize low loss multistate memory under an electric field. Fitting with the angular-dependence of the in-plane magnetization reveals that the magnetoelectric effect is dominated by the direct electric-field effect rather than the strain effect at the interface. The magnetoelectric effect and the induced surface anisotropy are found to be dependent on the Fe film thickness and are linear with respect to the applied electric field.

Novel properties of 5d transition metal oxides

The spin-orbit coupling (SOC) in the 5d transition metal element is expected to be strong due to the large atomic number and ability to modify the electronic structure drastically. On the other hand, the Coulomb interaction in 5d transition is non-negligible. Hence, the interplay of electron correlations and strong spin-orbit interactions make the 5d transition metal oxides (TMOs) specially interesting for possible novel properties. In this paper, we briefly summarize our theoretical studies on the 5d TMO. In section 2, we systematically discuss pyrochlore iridates. We find that magnetic moments at Ir sites form a non-colinear pattern with moment on a tetrahedron pointing to all-in or all-out from the center. We propose that pyrochlore iridates be Weyl Semimetal (WSM), thus providing a condensed-matter realization of Weyl fermion that obeys a two-component Dirac equation. We find that Weyl points are robust against perturbation and further reveal that WSM exhibits remarkable topological properties manifested by surface states in the form of Fermi arcs, which is impossible to realize in purely two-dimensional band structures. In section 3, based on density functional calculation, we predict that spinel osmates (AOs2O4,A=m Ca,Sr) show a large magnetoelectric coupling characteristic of axion electrodynamics. They show ferromagnetic order in a reasonable range of the on-site Coulomb correlation U and exotic electronic properties, in particular, a large magnetoelectric coupling characteristic of axion electrodynamics. Depending on U, other electronic phases including a 3D WSM and Mott insulator are also shown to occur. In section 4, we comprehensively discuss the electronic and magnetic properties of Slater insulator NaOsO3, and successfully predict the magnetic ground state configuration of this compound. Its ground state is of a G-type antiferromagnet, and it is the combined effect of U and magnetic configuration that results in the insulating behavior of NaOsO3 We also discuss the novel properties of LiOsO3, and suggest that the highly anisotropic screening and the local dipole-dipole interactions are the two most important keys to forming LiOsO3-type metallic ferroelectricity in section 5. Using density-functional calculations, we systematically study the origin of the metallic ferroelectricity in LiOsO3. We confirm that the ferroelectric transition in this compound is order-disorder-like. By doing electron screening analysis, we unambiguously demonstrate that the long-range ferroelectric order in LiOsO3 results from the incomplete screening of the dipole-dipole interaction along the nearest-neighboring Li-Li chain direction.

Self-biased large magnetoelectric coupling in co-sintered Bi0.5Na0.5TiO3 based piezoelectric and CoFe2O4 based magnetostrictive bilayered composite

In this work, magnetoelectric properties of a co-sintered bilayered composite of non-lead based piezoelectric 0.97(Bi0.5Na0.5TiO3)–0.03(K0.47Na0.47Li0.06Nb0.74Sb0.06Ta0.2O3) and magnetostrictive Co0.6Zn0.4Fe1.7Mn0.3O4 are presented. Similar optimal sintering conditions of the individual components lead to a very clean interface as evidenced in the scanning electron microscopy, angle dispersive X-ray diffraction, and energy-dispersive X-ray (EDX) results. Clean interface results in strong intimate mechanical coupling between both components and causes a maximum transfer of induced strain, leading to a large magnetoelectric coupling ∼142 mV/cm·Oe measured in longitudinally magnetized-transversely polarized configuration (L-T mode). Remnant polarization ∼32 μC/cm2, remnant magnetization ∼0.50 emu/g, and sufficiently high self biased magnetoelectricity ∼135 mV/cm Oe (L-T mode) were observed for this composite.

Orbital-ordering-driven multiferroicity and magnetoelectric coupling in GeV₄S₈.

We report here the discovery of multiferroicity and large magnetoelectric coupling in the type I orbital order system GeV₄S₈. Our study demonstrates that this clustered compound displays a para-ferroelectric transition at 32 K. This transition originates from an orbital ordering which reorganizes the charge within the transition metal clusters. Below the antiferromagnetic transition at 17 K, the application of a magnetic field significantly affects the ferroelectric polarization, revealing thus a large magnetoelectric coupling. Our study suggests that the application of a magnetic field induces a metamagnetic transition which significantly affects the ferroelectric polarization thanks to an exchange striction phenomenon.

A theoretical study of the nonlinear thermo-magneto-electric coupling effect in magnetoelectric laminates

For the tri-layer symmetric magnetoelectric (ME) laminates made of giant magnetostrictive materials and piezoelectric materials, we established a theoretical model for the nonlinear thermo-magneto-electric coupling effect in laminates. This model was nonlinear and calculated in an iterative approach. It adopted the nonlinear magneto-thermo-mechanical magnetostrictive constitutive and the linear mechanical-thermo-electric piezoelectric constitutive and introduced the interface coupling factor to describe the strain transfer efficiency between layers. The predictions of ME coefficient versus temperature curves coincide well with experiments qualitatively and quantitatively. This model then was adopted to predict the influences of the temperature, interface coupling factor and thermal expansion coefficient of the giant magnetostrictive materials on ME coupling. It showed that: the laminates had the strongest ME effect at 0 °C; increasing the coupling factor would contribute to obtaining a larger ME coupling in a smaller bias magnetic field and lowering the ME effect attenuation caused by temperature variations; a smaller thermal expansion coefficient was also conducive to obtaining a larger ME coupling in a smaller bias magnetic field and decreasing the ME effect attenuation caused by temperature variations. This model can provide a theoretical basis for the preparation and application of ME devices under different temperature conditions.

ChemInform Abstract: Multiferroics and Magnetoelectrics: A Comparison Between Some Chromites and Cobaltites

AbstractReview: 64 refs.

Magnetic-field-induced spin flop transition and magnetoelectric effect inCa2Fe2−xAlxO5

Magnetic-field-induced spin flop transition and magnetoelectric effect in noncentrosymmetric ${\text{Ca}}_{2}$${\text{Fe}}_{2\ensuremath{-}x}$${\text{Al}}_{x}$${\text{O}}_{5}$ (0.5 $\ensuremath{\le}$ $x$ $\ensuremath{\le}$ 1) single crystals have been investigated. Temperature dependence of magnetic susceptibility shows that the compounds have antiferromagnetic transition temperatures ${T}_{N}$ above room temperature. The spin easy axis varies from the $c$ axis to the $a$ axis with increasing Al content $x$. When a magnetic field is applied along the spin easy axis, a spin flop transition takes place, accompanied by anomalies in the electric polarization and dielectric constant. The anomalies can be ascribed to a noncollinear spin arrangement in the domain walls between two magnetic phases and/or the spin direction dependent modulation of the metal-ligand hybridization. Such a polarization change with a spin flop transition in polar antiferromagnets may provide a route to realize large magnetoelectric coupling at high temperatures.

Frequency Response of Longitudinal Magnetoelectric Effect in Piezoelectric-Magnetostrictive Clamping Structure Coupled through Normal Stress

Magnetoelectric (ME) materials have attracted continuous attention due to their potential applications in the fields of sensors, actuators, and transducers. A large ME coupling originated from a clamping structure was reported. ME coefficient of 0.95V cm1Oe1was obtained without amplifier at the planar acoustic frequency 60 KHz. The results show that large ME coupling can be obtained in the clamping structure through normal stress, and longitudinal ME effect could be better than transverse ME effect.

Large magnetoelectric coupling in ferromagnetic/ferroelectric superlattices with asymetric interfaces

In this Letter, we investigate an attractive approach providing large and cumulative magnetoelectric coupling in ferromagnetic/ferroelectric superlattice by inserting a monolayer of different metal (ferromagnetic or normal metal) at one interface. Using first-principles calculations on FeM/PbTiO3 (M=Ni, Pt and Ag) as a model system, the recorded high magnetoelectric coefficients are obtained in one unit cell with the insertion of Ni and Pt monolayer. A carefully analysis reveals that the large magnetoelectric effects are determined by combinations of several different mechanisms including interface bonding, spin-dependent screening, and distinct type of magnetic interactions.

Peculiar magnetism of BiFeO3 nanoparticles with size approaching the period of the spiral spin structure

Size effect of multiferroics is important for its potential applications in new type miniaturized multifunctional devices and thus has been widely studied. However, is there special size effect in the materials with spiral modulated spin structure (such as BiFeO3)? It is still an issue to be investigated. In this report, structural, magnetic and magnetoelectric coupling properties are investigated for sol-gel prepared BiFeO3 nanoparticles with various sizes. It is found that a structural anomaly arises for the particles with size close to the 62 nm period of the spiral modulated spin structure, which induces an obviously increased ferromagnetism. In addition, large magnetoelectric coupling effect is observed in 62 nm BiFeO3 nanoparticles. Our result provides another insight into the size effect of BiFeO3, and also a clue to the magnetic structure at nanoscale.

Multiferroics and Magnetoelectrics: A Comparison between Some Chromites and Cobaltites

Oxides containing magnetic 3d transition metals offer a large family of structures with frustrated magnetic networks. Some of those incommensurate antiferromagnetic structures are responsible for the local breaking of inversion symmetry so that these oxides are called spin-induced ferroelectrics. As listed in the introduction of this short review, the number of these multiferroics continues to increase. As for applications, the coupling between these ferroisms is needed; some magnetic oxides, despite a lack of ferroelectric ground state, exhibit large magnetoelectric coupling with a magnetic-field-induced polarization. Thus, they are classified as “magnetoelectrics”. In the present review, we focus on recently studied systems showing ferroelectric-like behaviors or large magnetoelectric coefficients. This will be illustrated by chromites with the comparison between ceramics of CuCrO2 and AgCrS2: they exhibit different antiferromagnetic ground states, centrosymmetric and noncentrosymmetric. For the magnetoelectrics, the example of the cobaltite, CaBaCo4O7, which is a polar ferrimagnet, is taken to illustrate the existence of large magnetoelectric coefficients in crystals. Then, the existence of spin-induced ferroelectricity in centrosymmetric orthochromites (RECrO3 with RE = Lu or Er) is discussed. Through this selection of potential multiferroics or magnetoelectrics, it is clear that many magnetic materials in different forms (bulk/crystal/thin film) remain to be studied.

Novel NiZnAl-ferrites and strong magnetoelectric coupling in NiZnAl-ferrite/PZT multiferroic heterostructures

Magnetic/piezoelectric multiferroic heterostructures with strong magnetoelectric (ME) coupling have recently attracted considerable interest. Since the ratio of magnetostriction λs over saturation magnetization Ms is a key factor to achieve strong magnetoelectric coupling in ferrite/piezoelectric multiferroic heterostructures, here we find a solution to tune λs/Ms by aluminum doping. We report aluminum-substituted NiZn-ferrites with different compositions (Ni0.65Zn0.35Fe2−xAlxO4, x = 0, 0.1, 0.3, 0.4, 0.6, 0.8 and 1) fabricated by a solid-state sintering process. The saturation magnetization of these NiZnAl-ferrites was reduced from 6000 to 900 G with increased Al doping, which was accompanied by a significantly narrowed ferromagnetic resonance linewidth from 1870 to 340 Oe. Meanwhile, saturation magnetostriction of these NiZnAl-ferrites was reduced from 6.67 to 1.40 ppm with increased amount of Al doping. Strong ME coupling was demonstrated in the NiZnAl-ferrites/PZT multiferroic heterostructures. A large piezoelectric deformation induced ferromagnetic resonance field change up to 42 Oe was observed in Ni0.65Zn0.35Fe1.2Al0.8O4/PZT heterostructures, corresponding to a large microwave ME coefficient of 4.2 Oe cm kV−1. These AlNiZn-ferrites and NiZnAl-ferrites/PZT heterostructures with large ME coupling provide a great opportunity for electrical tuning microwave devices.

Large Longitudinal Magnetoelectric Effect in Clamping Structure of TbDyFe Flake, Pb(Zr,Ti)O<sub>3</sub> Ring

Longitudinal magnetoelectric (ME) effect has been studied in a clamping structure of a magnetostrictive TbDyFe (Terfenol-D), a piezoelectric Pb(Zr,Ti)O3(PZT) ceramic ring. The ME coupling originates from the magnetic-mechanical-electric transform of the magnetostrictive effect in Terfenol-D and the piezoelectric effect in PZT by endpoint bonding, without adhesive layer. In such a clamping structure, Large induced voltage was measured without amplifier, Large longitudinal ME coefficient of 0.12V cm-1Oe-1was obtained at f =1 kHz, which is about 3 times larger than transverse ME coefficient of conventional layered Terfenol-D/PZT composites under the same measuring conditions. The ME coefficient reaches a maximum value at the dc bias magnetic field (Hdc) =280 Oe, which is lower than Hdc =350 Oe in conventional layered composites. The results show that large ME coupling can be achieved without adhesive layer, and longitudinal ME effect can be better than transverse ME effect.

Room-temperature magnetoelectric properties of Fe doped BaZr0.05Ti0.95O3

To explore the magnetoelectric effect in lead free bulk ceramics, solid solutions of BaZr0.05(FexTi1−3x/4)0.95O3 have been synthesized using conventional solid state reaction route with x = 0.000 to 0.020 in steps of 0.005. A small amount of Fe content shows an immense effect on properties of barium zirconium titanate. Room temperature X-ray diffraction studies substantiate the formation and purity of these polycrystalline samples in an orthorhombic crystal system. Temperature dependent dielectric study revealed a decrease in ferroelectric Curie temperature with a decrease in dielectric constant values as x varied from 0.000 to 0.020. Ferroelectricity is still maintained and well saturated loops are observed with Fe substitution at these levels; although the remnant polarization Pr values decrease substantially with increasing Fe content. The best value of magnetoelectric coupling coefficient (α) at room temperature is found to be 145.30 mV/cm.Oe for x = 0.015 sample. In conclusion, in a non-Pb based simple perovskite system a reasonably large magnetoelectric coupling is demonstrated.