Magnetoelectricity in multiferroics: a theoretical perspective

Abstract

The key physical property of multiferroic materials is the existence of a coupling between magnetism and polarization, i.e. magnetoelectricity. The origin and manifestations of magnetoelectricity can be very different in the available plethora of multiferroic systems, with multiple possible mechanisms hidden behind the phenomena. In this Review, we describe the fundamental physics that causes magnetoelectricity from a theoretical viewpoint.The present review will focus on the main stream physical mechanisms in both single phase multiferroics and magnetoelectric heterostructures. The most recent tendencies addressing possible new magnetoelectric mechanisms will also be briefly outlined.Magnetism and electricity are two fundamental physical phenomena which have been widely covered in elementary textbooks of electromagnetism and have led to a broad technological revolution within human civilization. Even today, these two crucial subjects remain at the frontier of active research, and are still attracting considerable attention within the scientific community for their indispensable scientific value and possible applications. In solids, magnetism and electricity originate from the spin and the charge degrees of freedom, respectively. The crossover between these two fascinating topics has much grown in recent years and it has developed into an emergent branch of Condensed Matter Physics calledGenerally speaking, magnetoelectric effects can exist in many systems, even in some that are nonmagnetic. In fact, the first example of a magnetoelectric effect was observed by Röntgen in 1888 in a dielectric material, which was magnetized when moving through an electric field [10]. Much more recently, the surface state of topological insulators was predicted to manifest magnetoelectric effects [11]. However, to develop magnetoelectricity of a large magnitude, and as a consequence of more considerable practical value, multiferroics seem to be the best playground. In multiferroics, both magnetic moments and electric dipole moments can be ordered, inducing robust macroscopic quantities such as magnetization and polarization. Moreover, crucially for applications, both moments are coupled. Then, these macroscopic quantities may be mutually controlled, for example modifying the magnetization by an electric voltage or modifying the polarization by a magnetic field, which is particularly useful to design new devices, such as for storage and sensors.However, conceptually the mere existence of multiferroics is highly non trivial [12]. For most magnetic materials, the magnetic moments arise from unpaired electrons in partially occupied d orbitals and/or f orbitals. However, the spontaneous formation of a charge dipole usually needs empty d orbitals as a condition of having a coordinate bond, i.e. the so-called d 0 rule. Thus, the key ions involved in typical magnetic materials and those in polar materials are different, making these two areas of research nearly isolated from each other. However, in 2003 the discovery of a large polarizatio...

Domains and domain walls in multiferroics

“…Additional functionalities arise at domain walls with a strong coupling between electric and magnetic degrees of freedom, enabling magnetic-field control of the local electronic charge state as discussed in Section 3 [36,39]. For a more comprehensive or more technical coverage of charged domain walls in ferroelectrics and multiferroics, we refer to recent reviews [40,56,62,63], and the specific studies highlighted in the following sections.…”

Topological Hall effect and emergent skyrmion crystal at manganite-iridate oxide interfaces

“…The presence of an interface DM interaction is supported by the small lattice mismatch at the interface (lattice constants of SIO and LSMO are 0.394 nm [27] and 0.388 nm [28], respectively) and a strain-dependent charge transfer [29]. Because of two approximate in-plane mirror symmetries, one mirror plane involves two Mn sites and another reflects two Mn sites, it is reasonable to expect that this DM vector lies in the plane of the interface [30,31]. Having an in-plane DM vector excludes the possibility of stabilizing a conical phase which typically appears in cubic systems such as MnSi [32,33].…”

Influence of XY anisotropy on a magnetoelectric effect in spin-1/2 XY chain in a transverse magnetic field

“…Magnetoelectrics are materials having both dielectric polarization and magnetization in a single phase and exhibiting a magnetoelectric effect (MEE), a vast class of phenomena of intercoupling of magnetization and polarization in matter [1][2][3][4]. These materials are particularly important for their application in spintronic devices [5,6].…”

“…In most interesting cases of non-trivial MEE, the magnetization (dielectric polarization) can be induced by only applying an electric (magnetic) field. Nowadays, several microscopic mechanisms of the MEE are known [1][2][3][4]. One of these mechanisms is based on the so-called spin-current model or inverse Dzyaloshinskii-Moriya (DM) model and was proposed in a seminal paper by Katsura, Nagaosa and Balatsky [7].…”