Manipulating the magnetic properties of MnBi₂Te₄ through electrochemical organic molecule intercalation

MnBi₂Te₄, 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 Bi₂Te₃ can tune its magnetism, synthesizing pure-phase MnBi₂Te₄ with uniform Bi₂Te₃ intercalation remains challenging, and the fixed interlayer spacing of Bi₂Te₃ limits magnetic coupling tunability. Here, we utilize electrochemical organic molecule intercalation to expand the van der Waals gap of MnBi₂Te₄ and modulate its magnetic properties. Through x-ray diffraction (XRD) characterizations, we confirm that the interlayer spacing of MnBi₂Te₄ 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-MnBi₂Te₄ 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-MnBi₂Te₄ shows robust ferromagnetism, with a Curie point (T_C) of 15 K, similar to that of the MnBi₂Te₄ monolayer. These results demonstrate that remarkable changes in the magnetic properties of MnBi₂Te₄ can be achieved via electrochemical intercalation, providing new insights into manipulating magnetism in layered magnetic materials.