Odd-even layer-number effect and layer-dependent magnetic phase diagrams in MnBi2Te4

TL;DR

This study reveals an odd-even layer-number effect in MnBi2Te4's magnetic properties, demonstrating layer-dependent magnetic phase diagrams and surface magnetization phenomena crucial for quantum applications.

Contribution

It provides the first detailed experimental and theoretical analysis of layer-dependent magnetism in MnBi2Te4, highlighting the odd-even layer effect and magnetic phase evolution.

Findings

Oscillations in coercivity and spin-flop transition with layer number

Anomalous magnetic hysteresis in even-layer septuples

Layer-dependent magnetic phase diagrams mapped to temperature and field

Abstract

The intrinsic magnetic layered topological insulator MnBi2Te4 with nontrivial topological properties and magnetic order has become a promising system for exploring exotic quantum phenomena such as quantum anomalous Hall effect. However, the layer-dependent magnetism of MnBi2Te4, which is fundamental and crucial for further exploration of quantum phenomena in this system, remains elusive. Here, we use polar reflective magnetic circular dichroism spectroscopy, combined with theoretical calculations, to obtain an in-depth understanding of the layer-dependent magnetic properties in MnBi2Te4. The magnetic behavior of MnBi2Te4 exhibits evident odd-even layer-number effect, i.e. the oscillations of the coercivity of the hysteresis loop (at {\mu}0Hc) and the spin-flop transition (at {\mu}0H1), concerning the Zeeman energy and magnetic anisotropy energy. In the even-number septuple layers, an anomalous magnetic hysteresis loop is observed, which is attributed to the thickness-independent surface-related magnetization. Through the linear-chain model, we can clarify the odd-even effect of the spin-flop field and determine the evolution of magnetic states under the external magnetic field. The mean-field method also allows us to trace the experimentally observed magnetic phase diagrams to the magnetic fields, layer numbers and especially, temperature. Overall, by harnessing the unusual layer-dependent magnetic properties, our work paves the way for further study of quantum properties of MnBi2Te4.