Manipulating the magnetic properties of MnBi ₂ Te ₄ through electrochemical organic molecule intercalation

Abstract MnBi 2 Te 4 , which is emerging as an intrinsic antiferromagnetic (AFM) topological insulator, provides a unique platform to investigate the interplay between magnetism and topology. Modulating its magnetic properties enables the observation of exotic quantum phenomena such as the quantum anomalous Hall effect, axion insulator states, and Majorana fermions. While the intercalation of Bi 2 Te 3 can tune its magnetism, synthesizing pure-phase MnBi 2 Te 4 with uniform Bi 2 Te 3 intercalation remains challenging, and the fixed interlayer spacing of Bi 2 Te 3 limits magnetic coupling tunability. Here, we utilize electrochemical organic molecule intercalation to expand the van der Waals gap of MnBi 2 Te 4 and modulate its magnetic properties. Through x-ray diffraction (XRD) characterizations, we confirm that the interlayer spacing of MnBi 2 Te 4 is expanded from 13.6 Å to 30.5 Å and 61.0 Å by intercalating quaternary ammonium cations (THA + and CTA + ), respectively. The THA-MnBi 2 Te 4 exhibits dual complex magnetic behavior, combining AFM ordering with a Néel temperature ( T N ) of 12 K and a small ferromagnetic hysteresis loop at 2 K. The CTA-MnBi 2 Te 4 shows robust ferromagnetism, with a Curie point ( T C ) of 15 K, similar to that of the MnBi 2 Te 4 monolayer. These results demonstrate that remarkable changes in the magnetic properties of MnBi 2 Te 4 can be achieved via electrochemical intercalation, providing new insights into manipulating magnetism in layered magnetic materials.