Electrically Controlled Anomalous Hall Effect and Orbital Magnetization in Topological Magnet MnBi2Te4

TL;DR

This paper investigates the intrinsic mechanisms behind the anomalous Hall effect and orbital magnetization in MnBi2Te4 thin films, revealing even-odd layer effects, magnetic transitions, and electrical switching phenomena.

Contribution

It introduces a microscopic model explaining the even-odd layer dependence and electrical switching in MnBi2Te4, highlighting the role of anti-ferromagnetic states and axion electrodynamics.

Findings

Opposite signs of anomalous Hall resistance in even and odd layers.

Identification of two magnetic transitions in even-layer films.

Observation of even-odd oscillation in magnetoelectric coefficient.

Abstract

In this work, we propose an intrinsic mechanism to understand the even-odd effect, namely the opposite signs of the anomalous Hall resistance and the different shapes of hysteresis loops for even and odd septuple layers (SLs), of MBE-grown MnBi2Te4 thin films with electron doping. In particular, we show that the non-zero hysteresis loops in the anomalous Hall and magnetic circular dichroism measurements for even-SLs MnBi2Te4 films are originated from two different anti-ferromagnetic (AFM) states with opposite magnetoelectric coefficients that give rise to different energies of zeroth Landau levels of the surface states in this model. The complex form of the anomalous Hall hysteresis loop in even-SLs MnBi2Te4 films can be understood from two magnetic transitions, a transition from one AFM state to the other AFM state followed by a second transition to the ferromagnetic state. Our model also provides a microscopic understanding of the electrical switching between two AFM states via the axion electrodynamics in even-SL MnBi2Te4 films. We further study orbital magnetization and magnetoelectric coefficient in MnBi2Te4 films, and find an even-odd oscillation behavior of the magnetoelectric coefficient.