  The antiferromagnetic topological insulator has attracted lots of attention
recently, as its intrinsic magnetism and topological property makes it a
potential material to realize the quantum anomalous Hall effect (QAHE) at
relative high temperature. Until now, only MnBi$_2$Te$_4$ is predicted and
grown successfully. The other MB$_2$T$_4$-family materials predicted
(MB$_2$T$_4$:M=transition-metal or rare-earth element, B=Bi or Sb, T=Te, Se, or
S) with not only antiferromagnetic topological property but also rich and
exotic topological quantum states and dynamically stable (or metastable)
structure have not been realized on experiment completely. Here, MnBi$_2$Te$_4$
single crystals have been grown successfully and tested. It shows typical
antiferromagnetic character, with Neel temperature of 24.5K and a spin-flop
transition at H$\thickapprox$35000 Oe, 1.8K. After obtaining MnBi$_2$Te$_4$
single crystals, we have tried to synthesize the other members of
MB$_2$T$_4$-family materials, but things are not going so well. Then it
inspires us to discuss the growth mechanism of MnBi$_2$Te$_4$. The growth mode
may be the layer-inserting growth mode based on symmetry, which is supported by
our X-ray photoelectron spectroscopy (XPS) measurement. The XPS measurement
combing with the $Ar^+$ ion sputtering is done to investigate the chemical
state of MnBi$_2$Te$_4$. Binding energies (BE) of the MnBi$_2$Te$_4$-related
contributions to Mn2p and Te3d spectra agree well with those of inserting
material $\alpha$-MnTe. Rising intensity of the Mn2p satellite for divalent Mn
(bound to chalcogen) with atomic number of ligand (from MnO to MnBi$_2$Te$_4$)
has been observed, thus suggesting classification of MnBi$_2$Te$_4$ as the
charge-transfer compound. Understanding the growth mode of MnBi$_2$Te$_4$ can
help us to grow the other members of MB$_2$T$_4$-family materials.
