Linear Magnetoelectric Effect Research Articles

Magnetoelectric hysteresis loops in Cr2O3at room temperature

We revisit the room-temperature linear magnetoelectric effect in Cr${}_{2}$O${}_{3}$ single crystals. It was found that the temperature dependence of dielectric constants in a magnetic field $H$ shows a \ensuremath{\lambda}-shaped peak at the N\'eel temperature (\ensuremath{\approx}307 K) and that electric polarization induced by applying $H$ is reversed with a hysteresis by sweeping an electric field $E$. Similar reversal and hysteretic behaviors were also observed in the $H$ dependence of magnetization induced by applying $E$. These results imply that Cr${}_{2}$O${}_{3}$ behaves as a typical ferroelectric (ferromagnet) in finite $H$ ($E$) even at room temperature. We discuss the ferroic behaviors observed in the linear magnetoelectric system in the context of recent studies on multiferroics.

Domain non-reciprocity of electromagnetic waves in a centrosymmetric TbMnO3

The polariton spectrum in a centrosymmetric TbMnO3 is considered at low temperatures in a commensurate antiferromagnetic state after the spin-flop transition in a magnetic field. It is shown that a linear dependence of the electric polarization P on a magnetic field H, observed in this state, is caused by ordering spins of the terbium ions. The magnetoelectric energy PGH (G is the antiferromagnetic vector of terbium) induces in a centrosymmetric TbMnO3 without a linear magnetoelectric effect the non-reciprocal spectrum of TM and TE polaritons. In antiferromagnetic 180° terbium domains, the speed of electromagnetic waves turns out to be different, and directions of the electric field precession and the polarization plane rotation have opposite signs. The order of these effects were found to be 10−3.

Resonance mixing of alternating current magnetic fields in a multiferroic composite

Theory for nonlinear mixing of harmonic magnetic fields in a ferromagnetic-ferroelectric composite structure has been developed and compared with data. In the voltage response of the composite, the model predicts a dc voltage proportional to the magnetostriction λ and its second derivative p with respect to the bias field H, an ac voltage due to linear magnetoelectric effect that is proportional to the piezomagnetic coefficient q, and a third term due to nonlinear mixing of the ac magnetic fields that is proportional to p. Doubling of the frequency and generation of voltages with sum and difference frequencies are expected due to nonlinearity of λ (H). The theoretically predicted effects are investigated in a sample of amorphous ferromagnetic film FeBSiC and a bimorph of lead zirconate titanate. Both the efficiency of frequency doubling and nonlinear mixing of the ac magnetic fields are found to be proportional to p. The effects discussed here are of interest for magnetic field sensors and signal processing devices such as mixers, frequency doublers, frequency dividers, and modulators.

Linear Magnetoelectric Effect by Orbital Magnetism

We use symmetry analysis and first-principles calculations to show that the linear magnetoelectric effect can originate from the response of orbital magnetic moments to the polar distortions induced by an applied electric field. Using LiFePO(4) as a model compound we show that spin-orbit coupling partially lifts the quenching of the 3d orbitals and causes small orbital magnetic moments (μ((L)) ≈ 0.3 μ(B)) parallel to the spins of the Fe(2+) ions. An applied electric field E modifies the size of these orbital magnetic moments inducing a net magnetization linear in E.

Limit on the Electron Electric Dipole Moment Using Paramagnetic FerroelectricEu0.5Ba0.5TiO3

We report on the results of a search for the electron electric dipole moment d(e) using paramagnetic ferroelectric Eu(0.5)Ba(0.5)TiO(3). The electric polarization creates an effective electric field that makes it energetically favorable for the spins of the seven unpaired 4f electrons of the Eu(2+) to orient along the polarization, provided that d(e) ≠ 0. This interaction gives rise to sample magnetization, correlated with its electric polarization, and is therefore equivalent to a linear magnetoelectric effect. A SQUID magnetometer is used to search for the resulting magnetization. We obtain d(e) = (-1.07 ± 3.06(stat) ± 1.74(syst)) × 10(-25) ecm, implying an upper limit of |d(e)|<6.05 × 10(-25) ecm (90% confidence).

First-order multi-kphase transitions and magnetoelectric effects in multiferroic Co3TeO6

A theoretical description of the sequence of magnetic phases in Co3TeO6 is presented. The strongly first-order character of the transition to the commensurate multiferroic ground state, induced by coupled order parameters corresponding to different wavevectors, is related to a large magnetoelastic effect with an exchange energy critically sensitive to the interatomic spacing. The monoclinic magnetic symmetry C2' of the multiferroic phase permits spontaneous polarization and magnetization as well as the linear magnetoelectric effect. The existence of weakly ferromagnetic domains is verified experimentally by second harmonic generation measurements.

Magnetoelectric effect in NdCrTiO5

We have measured the dielectric constant and the pyroelectric current of orthorhombic (space group $Pbam$) NdCrTiO${}_{5}$ polycrystalline samples. The dielectric constant and the pyroelectric current show features associated with ferroelectric transitions at the antiferromagnetic transition temperature (${T}_{N}$ $=$ 21 K). The effect of magnetic fields is to enhance the features almost linearly up to the maximum measured field (7 T) with a spontaneous polarization value of $\ensuremath{\sim}$3.5 $\ensuremath{\mu}$C/m${}^{2}$. Two possible scenarios, the linear magnetoelectric effect and multiferroicity (antiferromagnetism plus ferroelectricity), are discussed as possible explanations for the observations.

Nonlinear–Linear Transition of Magnetoelectric Effect in Magnetic Graphene Nanoflakes on Substrates

Linear magnetoelectric (ME) effect provides an ideal way to control magnetism by an external electric field and has long been pursued in spintronics. However, the essential conditions for linear ME effects are still not well understood, especially for the newly emerged metal-free ME systems. Here, using density functional theory calculations, we reveal a novel nonlinear–linear transition of the ME effect in graphene nanoflakes (GNFs) placed on substrates with different chemical activities. We show that the ME effect is nonlinear in a magnetic GNF on graphene substrate. Interestingly, the ME effect in the same GNF becomes highly linear with markedly increased ME coefficient when an h-BN sheet is inserted between the GNF and graphene layer. We reveal that the weak electronic hybridization between the GNFs and substrate is the essential mechanism for the linear ME behavior in the graphene-based magnets. The tunable nonlinear–linear transition in ME coupling opens up new opportunities to fabricate and manipulate high-quality ME devices.

(Invited) Properties of Oxide Heterostructures

We present theoretical and experimental studies of three oxide heterostructures: LaAlO3/EuO heterojunction, Fe/BaTiO3/Pt superlattice and epitaxial LaCoO3 on (100)-oriented silicon. We use density functional theory (DFT) to predict the physical properties of the heterostucture and molecular beam epitaxy (MBE) to realize it in practice. We predict spin polarized two dimensional electron gas at the LaAlO3/EuO interface, linear magnetoelectric effect in a Fe/BaTiO3/Pt superlattice, and predict and demonstrate experimentally strain stabilized ferromagnetism in LaCoO3 on silicon.

Studies on multiferroic materials in high magnetic fields

In this article, studies on the magnetoelectric effects of multiferroic materials in high magnetic fields, particularly pulsed magnetic fields, are discussed and results for some representative materials are presented. In the discussions on representative materials, the relationship between the crystallographic symmetry and the linear magnetoelectric effect in Cr2O3 is introduced. Then drastic changes in polarization caused by magnetic transitions are discussed through a case study of manganites with a perovskite-type structure. In addition, high field studies on the magnetoelectric effects in BiFeO3, which is an exceptional multiferroic material, are presented and discussed in the framework of the Landau-Ginzburg theory.

The magnetic structure of multiferroicBaMnF4

The multiferroic material BaMnF4 has been investigated with unpolarized and polarized neutron diffraction. The structurehas been shown to be antiferromagnetic. The magnetic moments are aligned at12° to theb directionin the bc plane, 3° different from the previously determined value. The ferromagnetic component that isindicative of the linear magnetoelectric effect was not observed.

Spin-Driven Ferroelectricity and Magneto-Electric Effects in Frustrated Magnetic Systems

The interplay between magnetism and electricity in matter has become a central issue of condensed-matter physics. This review focuses on the ferroelectricity induced by magnetic order mostly in frustrated magnets, which is nowadays referred to as magneto-electric (ME) multiferroic, or often only as multiferroic. Some distinct types of microscopic origins relevant to the spin-driven ferroelectricity are discussed in detail. Then one sees that the frustration-based spin-driven ferroelectrics can exhibit nonlinear and giant ME responses of phase-transition type and of domain-control type, in contrast to the conventional magnetoelectrics hosting linear ME effects.

Magnetoelectric coupling in MnTiO3

We give general arguments that show that the linear magnetoelectric effect in antiferromagnetic materials gives rise to a magnetocapacitance anomaly---a divergence of the dielectric constant at the magnetic ordering temperature ${T}_{N}$ that appears in an applied magnetic field. The measurement of magnetodielectric response thus provides a definitive and experimentally accessible method to recognize antiferromagnetic linear magnetoelectric materials, circumventing the experimental difficulties often involved in measuring electric polarization. We confirm this result experimentally using the example of MnTiO${}_{3}$, which we show to exhibit the linear magnetoelectric effect. No dielectric anomaly is observed at ${T}_{N}$ in the absence of an applied magnetic field. However, a sharp peak in the dielectric constant appears here when a magnetic field is applied along the $c$ axis, reflecting a linear coupling of the polarization $P$ with the antiferromagnetic order parameter $L$. In accordance with our theoretical analysis, the dielectric constant close to ${T}_{N}$ increases with the square of the magnetic field.

Surface Effects on Morin Transition, Exchange Bias, and Enchanced Spin Reorientation in Chemically Synthesized DyFeO3 Nanoparticles

A giant linear magnetoelectric effect was observed by Y. Tokura’s group recently in multiferroic DyFeO3, which demands a detailed investigation of its magnetic properties. Additionally, there is little information on the changes of chemical and physical properties of these materials with the reduction in particle size in spite of the potential applications of these materials in nanoscale devices. As the wet-chemical synthesis of these materials in nanosize and getting a control over crystallinity and stoichiometry is nontrivial and poses a serious challenge prohibiting the study of their size-dependent properties. Here, we report the synthesis of DyFeO3 nanoparticles using a surfactantless hydrothermal method with a detailed magnetic property measurement. The as-synthesized DyFeO3 nanoparticles showed excellent crystallinity with average particle size in the range 50−60 nm. The structural analysis indicated that they are of a distorted orthorhombic pervoskite crystal structure. Detailed dc magnetization m...

Complete Symmetry Analyses of the Surface-Induced Piezomagnetic, Piezoelectric and Linear Magnetoelectric Effects

The impact of the surface on the magnetic symmetry is studied. It is shown how symmetry breaking transforms the “seeding” 90 bulk magnetic classes, which include 66 piezomagnetic classes and 58 magnetoelectric classes, into the 21 surface-induced magnetic classes, which all are piezomagnetic, piezoelectric and 19 of them are linear magnetoelectric. So, the new piezomagnetic, piezoelectric properties and linear magnetoelectric coupling should appear in nanosystems, where the impact of surface dominates over the bulk properties.

Multiferroic and magnetoelectric materialsߞnovel developments and perspectives

Magnetoelectric (ME) materials are of utmost interest in view of both fundamental understanding and novel desirable applications. Despite its smallness, the linear ME effect has been shown to control spintronic devices very efficiently, e.g., by using the classic ME antiferromagnet Cr₂O₃. Similar nano-engineering concepts exist also for type-I multiferroic single phase materials like BiFeO₃ and BiMnO₃. Record high ME response has been realized in stress-strain coupled multiphase magnetoelectrics like PZT/FeBSiC composites, enabling applications in sensors. In type-II multiferroics, whose ferroelectricity is due to modulated magnetic ordering, the ME coupling is of fundamental interest. Higher-order ME response characterizes disordered systems, which extend the conventional multiferroic scenario toward ME multiglass (e.g., Sr(1-x)MnxTiO₃).

Temperature-Dependent Magnetoelectric Effect from First Principles

We show that nonrelativistic exchange interactions and spin fluctuations can give rise to a linear magnetoelectric effect in collinear antiferromagnets at elevated temperatures that can exceed relativistic magnetoelectric responses by more than 1 order of magnitude. We show how symmetry arguments, ab initio methods, and Monte Carlo simulations can be combined to calculate temperature-dependent magnetoelectric susceptibilities entirely from first principles. The application of our method to Cr2O3 gives quantitative agreement with experiment.

Surface-induced piezomagnetic, piezoelectric, and linear magnetoelectric effects in nanosystems

Using symmetry theory we explore how symmetry breaking inevitably present in the vicinity of any surface gives rise to spontaneous surface piezomagnetic, piezoelectric, and magnetoelectric effects. The large surface-to-volume ratio makes the surface symmetry effects dominant in small enough nanosystems. As a result piezomagnetism, piezoelectricity, and strong size-dependent linear magnetoelectric coupling are predicted in nanomaterials, which are nonpiezomagnetic and/or nonpiezoelectric in the bulk, but belong to the one of the existing 90 bulk magnetic classes, e.g., among a wide class of cubic binary oxides such as MnO, FeO, CoO, NiO, EuO, PrO, and ${\text{Er}}_{2}{\text{O}}_{3}$.

Magnetoelectricity in the ferrimagnetic Cu2OSeO3: symmetry analysis and Raman scattering study

sublattices ferrimagnet Cu2OSeO3 with a cubic symmetry and a linear magnetoelectric effect. There is no spectroscopic evidence for structural lattice distortions below TC=60K, which are expected due to magnetoelectric coupling. Using symmetry arguments we explain this observation by considering a special type of ferrimagnetic ground state which does not generate a spontaneous electric polarization. Interestingly, Raman scattering shows a strong increase of electric polarization of media through a dynamic magnetoelectric effect as a remarkable enhancement of the scattering intensity below TC. New lines of purely magnetic origin have been detected in the magnetically ordered state. A part of them are attributed as scattering on exchange magnons. Using this observation and further symmetry considerations we argue for strong Dzyaloshinskii–Moriya interaction existing in the Cu2OSeO3.

Symmetry and magnetoelectric interactions in BaMnF4

Symmetry analysis is used to study magnetic anisotropy and magnetoelectric interactions in the ferroelectric antiferromagnet BaMnF4 theoretically. It is shown that symmetry admits the existence in this material of a nonuniform magnetoelectric interaction (flexomagnetoelectric type) with a specific dependence on the magnitude and orientation of the external magnetic field. With increasing magnetic field this interaction can cause a phase transition into a magnetic incommensurate phase with a characteristic jump of the electric polarization. The linear and quadratic magnetoelectric effects and the question of the relativistic canting of the sublattices, which is due to the magnetoelectric interaction, are examined. The proposed approach is a natural generalization of the method of constructing invariants from the magnetic modes of the crystal to the case of phase transitions with a doubled unit cell of the crystal and can be used for symmetry analysis of other ferroelectric magnetic compounds.