The re-entrant ferromagnetism due to symmetric exchange bias in two septuple-layer MnBi2Te4 epitaxial films

TL;DR

This study reveals complex magnetic phenomena in ultra-thin MnBi2Te4 films, including re-entrant ferromagnetism driven by symmetric exchange bias caused by anti-site defects, expanding understanding of magnetic topological insulators.

Contribution

It uncovers re-entrant ferromagnetism in MnBi2Te4 films linked to symmetric exchange bias from anti-site defects, a novel magnetic behavior in this material.

Findings

Re-entrant ferromagnetism observed in two-septuple-layer MBT films.

Symmetric exchange bias effect attributed to Mn-on-Bi anti-site defects.

All MBT films exhibit spin-glass-like behaviors.

Abstract

MnBi2Te4 (MBT) is a typical magnetic topological insulator with an A-type antiferromagnetic (AFM) ground state. Here we prepared ultra-thin MBT films with controlled anti-site defects and observed rich doping-dependent magnetic behaviors. We find in one-septuple-layer MBT films a ferrimagnetic ground state and in two-septuple-layer ones a kind of re-entrant ferromagnetism (FM) that disappears with increased Bi-on-Mn doping in the FM Mn-layers. This re-entrant behavior is attributed to a kind of symmetric exchange-bias effect that arises in the presence of both AFM and FM sub-systems due to the introduction of high-dense Mn-on-Bi anti-site defects. Furthermore, all MBT films display spin-glass-like behaviors. Our work demonstrates rich magnetic behaviors originating from the competing magnetic interactions between Mn spins at different lattice positions in MBT.