Topological solitons and bulk polarization switch in collinear type II multiferroics

TL;DR

This paper presents a microscopic model for collinear multiferroics that explains magnetic frustration, lattice distortions, and dipolar interactions, leading to a switchable bulk polarization driven by magnetic fields, with topological magnetic excitations ensuring robustness.

Contribution

It introduces a new microscopic model capturing the interplay of magnetic frustration, lattice distortions, and dipolar interactions in multiferroics, revealing a topologically robust polarization switching mechanism.

Findings

Lattice dimerization induces a spontaneous Z2 ferrielectric polarization.

Magnetic field above a critical value switches off the polarization.

Topological magnetic excitations confer robustness to the mechanism.

Abstract

We introduce a microscopic model for collinear multiferroics capable to reproduce, as a consequence of magnetic frustration and easy-axis anisotropy, the so-called "uudd" (or antiphase) magnetic ordering observed in several type II multiferroic materials. The crucial role of lattice distortions in the multiferroic character of these materials is entered into the model via an indirect magnetoelectric coupling, mediated by elastic degrees of freedom through a pantograph mechanism. Long range dipolar interactions set electric dipoles in the antiferroelectric order. We investigate this model by means of extensive DMRG computations and complementary analytical methods. We show that a lattice dimerization induces a spontaneous Z2 ferrielectric bulk polarization, with a sharp switch off produced by a magnetic field above a critical value. The topological character of the magnetic excitations makes this mechanism robust.