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Vapor transport growth of MnBi2Te4 and related compounds

Motivated by fine tuning of the magnetic and topological properties of MnBi$_2$Te$_4$ via defect engineering, in this work, we report the crystal growth of MnBi$_2$Te$_4$ and related compounds using vapor transport method and characterization of vapor transported crystals by measuring elemental analysis, magnetic and transport properties, and scanning tunneling microscopy. For the growth of MnBi$_2$Te$_4$ single crystals, I$_2$, MnI$_2$ , MnCl$_2$, TeCl$_4$, or MoCl$_5$ are all effective transport agents; chemical transportation occurs faster in the presence of iodides than chlorides. MnBi$_2$Te$_4$ crystals can be obtained in the temperature range 500$^\circ$C-590$^\circ$C using I$_2$ as the transport agent. We further successfully grow MnSb$_2$Te$_4$, MnBi$_{2-x}$Sb$_x$Te$_4$, and Sb-doped MnBi$_4$Te$_7$ crystals. A small temperature gradient $<$20$^\circ$C between the hot and cold ends of the growth cmpoule is critical for the successful crystal growth of MnBi$_2$Te$_4$ and related compounds. Compared to flux grown crystals, vapor transported crystals tend to be Mn stoichiometric, and Sb-bearing compositions have more Mn/Sb site mixing. The vapor transport growth provides a new materials synthesis approach to fine tuning the magnetic and topological properties of these intrinsic magnetic topological insulators.