Metastable MnBi$_2$Te$_4$ enabled by magnetic-field-assisted synthesis

TL;DR

This study demonstrates that applying a magnetic field during synthesis transforms MnBi$_2$Te$_4$ from an antiferromagnetic to a ferromagnetic state, altering its electronic properties.

Contribution

It introduces a magnetic-field-assisted synthesis method to control the magnetic ground state of MnBi$_2$Te$_4$, a topological insulator.

Findings

Field-grown MnBi$_2$Te$_4$ exhibits ferromagnetism with a Curie temperature of ~12.5 K.

Magnetic-field-assisted synthesis reconfigures the spin order without changing crystal structure.

Electronic properties are modified, evidenced by de Haas-van Alphen oscillations.

Abstract

Magnetic topological insulators provide a unique platform to explore the interplay between magnetism and topology. MnBi$_2$Te$_4$, known for its A-type antiferromagnetic (AFM) ground state, undergoes a striking transformation when single crystals are grown in an applied magnetic field. Despite retaining the same crystal structure, field-grown MnBi$_2$Te$_4$ exhibits a ferromagnetic (FM) ground state with a Curie temperature of $\sim$ 12.5 K, confirmed by magnetization, magnetic torque, electrical resistivity, and specific heat measurements. First-principles calculations support these findings, revealing that magnetic-field-assisted synthesis can effectively reconfigure the ground-state spin order and thereby modify the material's electronic properties, as reflected in the de Haas-van Alphen oscillation seen in the magnetic torque.