Intermixing-driven surface and bulk ferromagnetism in the quantum anomalous Hall candidate MnBi$_6$Te$_{10}$

TL;DR

This study investigates the magnetic properties of MnBi$_6$Te$_{10}$, revealing robust ferromagnetism driven by Mn/Bi intermixing, with implications for realizing the quantum anomalous Hall effect at higher temperatures.

Contribution

The paper demonstrates the origin of ferromagnetism in MnBi$_6$Te$_{10}$ through experimental and theoretical analysis, highlighting the role of Mn/Bi intermixing and surface magnetism.

Findings

MnBi$_6$Te$_{10}$ exhibits ferromagnetism with $T_C \\approx 12$ K.

Surface magnetism remains intact with a large magnetic moment.

Intermixing of Mn and Bi drives the ferromagnetic properties.

Abstract

The recent realizations of the quantum anomalous Hall effect (QAHE) in MnBi$_2$Te$_4$ and MnBi$_4$Te$_7$ benchmark the (MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$ family as a promising hotbed for further QAHE improvements. The family owes its potential to its ferromagnetically (FM) ordered MnBi$_2$Te$_4$ septuple layers (SL). However, the QAHE realization is complicated in MnBi$_2$Te$_4$ and MnBi$_4$Te$_7$ due to the substantial antiferromagnetic (AFM) coupling between the SL. An FM state, advantageous for the QAHE, can be stabilized by interlacing the SL with an increasing number $n$ of Bi$_2$Te$_3$ layers. However, the mechanisms driving the FM state and the number of necessary QLs are not understood, and the surface magnetism remains obscure. Here, we demonstrate robust FM properties in MnBi$_6$Te$_{10}$ ($n = 2$) with $T_C \approx 12$ K and establish their origin in the Mn/Bi intermixing phenomenon by a combined experimental and theoretical study. Our measurements reveal a magnetically intact surface with a large magnetic moment, and with FM properties similar to the bulk. Our investigation thus consolidates the MnBi$_6$Te$_{10}$ system as perspective for the QAHE at elevated temperatures.