Mn-rich MnSb2Te4: A topological insulator with magnetic gap closing at high Curie temperatures of 45-50 K

TL;DR

This study demonstrates that Mn-rich MnSb2Te4 is a ferromagnetic topological insulator with a high Curie temperature of 45-50 K, featuring a Dirac cone, out-of-plane spin polarization, and a magnetically induced band gap closing at the Curie point.

Contribution

It reveals that MnSb2Te4 with Mn excess is a ferromagnetic topological insulator with record high Curie temperature, distinct from previous antiferromagnetic MnBi2Te4, and elucidates its electronic and magnetic properties.

Findings

Record high Curie temperature of 45-50 K for MnSb2Te4

Presence of a Dirac cone with the Dirac point near the Fermi level

Magnetically induced band gap closes at the Curie temperature

Abstract

Ferromagnetic topological insulators exhibit the quantum anomalous Hall effect that might be used for high precision metrology and edge channel spintronics. In conjunction with superconductors, they could host chiral Majorana zero modes which are among the contenders for the realization of topological qubits. Recently, it was discovered that the stable 2+ state of Mn enables the formation of intrinsic magnetic topological insulators with A1B2C4 stoichiometry. However, the first representative, MnBi2Te4, is antiferromagnetic with 25 K N\'eel temperature and strongly n-doped. Here, we show that p-type MnSb2Te4, previously considered topologically trivial, is a ferromagnetic topological insulator in the case of a few percent of Mn excess. It shows (i) a ferromagnetic hysteresis with record high Curie temperature of 45-50 K, (ii) out-of-plane magnetic anisotropy and (iii) a two-dimensional Dirac cone with the Dirac point close to the Fermi level which features (iv) out-of-plane spin polarization as revealed by photoelectron spectroscopy and (v) a magnetically induced band gap that closes at the Curie temperature as demonstrated by scanning tunneling spectroscopy. Moreover, it displays (vi) a critical exponent of magnetization beta~1, indicating the vicinity of a quantum critical point. Ab initio band structure calculations reveal that the slight excess of Mn that substitutionally replaces Sb atoms provides the ferromagnetic interlayer coupling. Remaining deviations from the ferromagnetic order, likely related to this substitution, open the inverted bulk band gap and render MnSb2Te4 a robust topological insulator and new benchmark for magnetic topological insulators.