Magnetization reversal through an antiferromagnetic state

TL;DR

This paper introduces a novel magnetization reversal pathway mediated by an antiferromagnetic state, revealing atomic-scale magnetization compensation at coercive fields in Fe$_2$Mo$_3$O$_8$, with implications for advanced magnetization control.

Contribution

It demonstrates a new reversal mechanism involving an antiferromagnetic phase, supported by experimental and microscopic theoretical analysis, distinct from traditional domain-based processes.

Findings

Antiferromagnetic phase emerges at coercive fields.

Reappearance of magnon mode during reversal.

Atomic-scale magnetization compensation observed.

Abstract

Magnetization reversal in ferro- and ferrimagnets is a well-known archetype of non-equilibrium processes, where the volume fractions of the oppositely magnetized domains vary and perfectly compensate each other at the coercive magnetic field. Here, we report on a fundamentally new pathway for magnetization reversal that is mediated by an antiferromagnetic state. Consequently, an atomic-scale compensation of the magnetization is realized at the coercive field, instead of the mesoscopic or macroscopic domain cancellation in canonical reversal processes. We demonstrate this unusual magnetization reversal on the Zn-doped polar magnet Fe$_2$Mo$_3$O$_8$. Hidden behind the conventional ferrimagnetic hysteresis loop, the surprising emergence of the antiferromagnetic phase at the coercive fields is disclosed by a sharp peak in the field-dependence of the electric polarization. In addition, at the magnetization reversal our THz spectroscopy studies reveal the reappearance of the magnon mode that is only present in the pristine antiferromagnetic state. According to our microscopic calculations, this unusual process is governed by the dominant intralayer coupling, strong easy-axis anisotropy and spin fluctuations, which result in a complex interplay between the ferrimagnetic and antiferromagnetic phases. Such antiferro-state-mediated reversal processes offer novel concepts for magnetization control, and may also emerge for other ferroic orders.