Guiding novel magnetic ground states of MnBi₂Te₄ via an external magnetic field

MnBi₂Te₄ is a well-known magnetic topological insulator with an antiferromagnetic (AFM) ground state, though other magnetic states lie close in energy. This raises the question: can these alternative states be accessed via an external magnetic field? We synthesized and post-treated single-crystalline MnBi₂Te₄ under various conditions, resulting in novel magnetic ground states. By annealing the single crystals at 600 K at 10 Tesla, a superparamagnetic state is stabilized. Growing MnBi₂Te₄ single crystals under 9 Tesla results in the same structure as the AFM phase but exhibiting a ferromagnetic (FM) ground state with a Curie temperature of approximately 12 K. Magnetization, magnetic torque, and specific heat measurements confirm its magnetic properties, supported by first-principles and spin dynamics calculations. These findings show that applying a magnetic field during synthesis or post annealing can reconfigure the ground-state spin structure, thereby influencing the material’s topological properties.