Defect-Assisted Domain Nucleation Drives Unique Exchange Bias Phenomena in $\bf{MnBi_2Te_4}$

TL;DR

This paper uncovers a novel, defect-assisted exchange bias mechanism in ultrathin MnBi₂Te₄, demonstrating tunable magnetic properties through domain engineering, with implications for advanced spintronic device design.

Contribution

It reveals a new defect-mediated exchange bias phenomenon in MnBi₂Te₄, controllable without field cooling, combining experimental and theoretical insights.

Findings

Exchange bias magnitude and direction are tunable via magnetic field protocols.

Defect-induced pinning domains facilitate the observed exchange bias.

Temperature and thickness influence the exchange bias behavior.

Abstract

The study of the mechanism of exchange bias phenomena and the achievement of its efficient control are of great importance, as it promotes the revelation of unique exchange interactions and the development of exotic applications. However, it is challenging due to the elusive interface between magnetic phases. In this study, we report an unprecedented exchange bias phenomenon observed in ultrathin uncompensated antiferromagnetic MnBi$_2$Te$_4$. The magnitude and direction of the exchange field can be intentionally controlled by designing a magnetic field sweep protocol without a field cooling process. The combined experimental and theoretical simulation results indicate that the spin-flip process assisted by the ubiquitous defect-induced pinning domain sites with varying inner exchange interactions might give rise to the emergence and robustness of this peculiar exchange bias. The temperature and thickness dependence of the exchange bias phenomena are systematically investigated for further study and exploitation of its unique properties. This mechanism hold promise for highly tunable exchange bias in prevalent magnetic systems by engineering the properties of domain structures, and also offers promising avenues for the design of spintronic devices combing its topology based on MnBi$_2$Te$_4$.