Tuning the magnetism and band topology through antisite defects in Sb doped MnBi4Te7

TL;DR

This study demonstrates how Sb-doping in MnBi4Te7 tunes its magnetic states from antiferromagnetic to ferromagnetic and ferrimagnetic, while also modifying its band topology, enabling exploration of novel magnetic topological phases.

Contribution

It reveals the role of antisite defects in controlling magnetism and band topology in MnBi4Te7, combining experimental and first-principles calculations for the first time.

Findings

Sb-doping induces a transition from antiferromagnetic to ferromagnetic and ferrimagnetic states.

Antisite defects modify the band topology, enabling the realization of magnetic Weyl semimetals.

Doping series offers a platform for studying quantum anomalous Hall effect and Fermi arc states.

Abstract

The fine control of magnetism and electronic structure is crucial since the interplay between magnetism and band topology can lead to various novel magnetic topological states including axion insulators, magnetic Weyl semimetals and Chern insulators etc. Through crystal growth, transport, thermodynamic, neutron diffraction measurements, we show that with Sb-doping, the newly-discovered intrinsic antiferromagnetic topological insulator MnBi4Te7 evolves from antiferro-magnetic to ferromagnetic and then ferrimagnetic. We attribute this to the formation of Mn(Bi,Sb) antisites upon doping, which result in additional Mn sublattices that modify the delicate interlayer magnetic interactions and cause the dominant Mn sublattice to go from antiferromagnetic to ferro-magnetic. We further investigate the effect of antisites on the band topology using the first-principles calculations. Without considering antisites, the series evolves from antiferromagnetic topological insulator (x = 0) to ferromagnetic axion insulators. In the exaggerated case of 16.7% of periodic antisites, the band topology is modified and type-I magnetic Weyl semimetal phase can be realized at intermediate dopings. Therefore, this doping series provides a fruitful platform with continuously tunable magnetism and topology for investigating emergent phenomena, including quantum anomalous Hall effect, Fermi arc states, etc.