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 (T_c) 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.