Phase-controlled growth of 2D crystals of the MB2T4 family via a flux-assisted method.

Van der Waals materials of the MB2T4 family (M = transition metal or rare-earth metal, B = Bi or Sb, T = Te, Se, or S) have attracted wide interest for their exotic topological and magnetic properties, as well as potential spintronic applications. However, the direct growth of 2D ternary MB2T4 remains challenging due to multiple competing phases and complex atomic arrangements. Here, we report a flux-assisted, phase-controlled growth strategy to directly grow six distinct 2D MB2T4 crystals. Using MB2T4 bulk powder as precursor, its dissolution into the cosolvent ensures stoichiometric control, while thermodynamic-kinetic equilibrium suppresses phase separation. Taking MnSb2Te4 as an example, we obtained highly ordered septuple layers, with superconducting quantum interference device (SQUID) and reflective magnetic circular dichroism (RMCD) measurements confirming layer-dependent ferromagnetism and Curie temperature (Tc) ranging from 12.3 to 33.7 K. This strategy provides an effective route for synthesizing complex layered crystals and offers versatile platforms for advancing spintronic applications.