Study of the effect of Mn:Bi ratio in the growth of MnBi2Te4 bulk crystals

The antiferromagnetic topological insulator MnBi 2 Te 4 has drawn great interest in recent years. However, techniques for the growth of sizeable single crystals still need to be improved. Mn:Bi ratio or MnTe:Bi 2 Te 3 ratio in the starting material is an important factor that affects the outcome of synthesis. We employed a relatively simple self-flux method that uses the three elements directly and involves only one sintering procedure. We systematically studied the crystals obtained with different Mn:Bi ratio, from 1:2 (the stoichiometric ratio) to 1:20. Structural characterization shows the shift in the chemical compositions, from entirely MnBi 2 Te 4 septuple-atomic layers, to the MnBi 4 Te 7 structure and finally to Mn-doped Bi 2 Te 3 . Hybrid crystals with multiple types of structures are found among them. The relation between the results and the starting material ratios is summarized, and can provide useful reference for the crystal growth and future researches in this area.