Polar magnetic oxides from chemical ordering: A new class of multiferroics

Abstract

Combining ferroelectricity and magnetism in the same material remains a challenge because it involves complex crystal chemistry and stringent symmetry requirements. In conventional ferroelectrics, the polarization arises from the second-order Jahn–Teller effect associated with cations of d0 or s2 lone pair electronic configuration. In contrast, the magnetism arises from cations with partially filled d or f electrons. Materials that incorporate these two kinds of cations in different crystallographic sites exhibit multiferroic properties but with weak coupling between magnetism and ferroelectricity. On the other hand, a strong cross-coupling occurs in some materials, where specific spin structures induce weak ferroelectricity below the magnetic ordering temperature. In this article, we discuss a new class of multiferroics where the polar distortion results from chemical ordering. These polar oxides are mainly pyroelectric in the entire temperature range and exhibit magnetoelectric coupling below the magnetic ordering temperatures.

Hybrid Multiferroic Behavior in the Double Perovskite (Ca0.5Mn1.5)MnWO6

“…A new group, type III multiferroics, was recently introduced to emphasize materials that are always polar. , In other words, polar structures are fixed by chemical orders in them and, therefore, they do not show temperature-driven ferroelectric (or nonpolar-to-polar structural) transitions. In many cases, they are not ferroelectric (as polarization cannot be switched by an external electric field), but they are pyroelectric.…”

Magnetocapacitance effect and magnetoelectric coupling in type-II multiferroic HoFeWO6

“…It was proposed that these compounds should be classified as type III, a new class of multiferroics, in order to distinguish them from type II, in which the paramagnetic region is centrosymmetric and the magnetic ordering breaks the inversion symmetry, inducing a spontaneous polarization that is coupled to the magnetic field [29].…”

Introduction to the Department of Cardiology in Nanjing First Hospital of Nanjing Medical University, China

“…Until recently, the polar magnets have been recognized as the promising playground to search for new multiferroics with large ME effects and emergent physical phenomena, such as giant thermal Hall effect [11], antiferromagnetic solutions [12,13], nonreciprocal effect [14,15], and topological quasiparticle skyrmions [16][17][18][19]. In contrast to the type-I multiferroics, e.g., BiFeO3 [20] and hexagonal YMnO3 [21], where the polar distortion is caused by nonmagnetic ions, the polar distortion in the polar ME materials is usually associated with the magnetic ions [22], thus strong magnetoelectric coupling can be expected.…”