Compositional Control and Optimization of Molecular Beam Epitaxial Growth of (Sb2Te3)x(MnSb2Te4)y Magnetic Topological Insulators

Magnetic topological insulators such as MnBi2Te4 and MnSb2Te4 are promising hosts of novel physical phenomena such as quantum anomalous Hall effect and intrinsic axion insulator state, both potentially important for the implementation in topological spintronics and error-free quantum computing. In the bulk, the materials are antiferromagnetic but appropriate stacking with non-magnetic layers or excess Mn in the crystal lattice can induce a net ferromagnetic alignment. In this work we report the growth of (Sb2Te3)x(MnSb2Te4)y layers with varying Mn content by molecular beam epitaxy. The Mn flux fraction provided during growth controls the percent of MnSb2Te4 that is formed in the resulting layers by a self-assembly process. Highly crystalline layers with compositions varying between Sb2Te3 (y=0) and MnSb2Te4 (x=0) were obtained. The results show that Mn incorporates as a structural component to form MnSb2Te4, and as an impurity element both in Sb2Te3 and in MnSb2Te4. Two modifications of the growth conditions were implemented to enhance the incorporation of Mn as a structural element to form MnSb2Te4. Annealing of a thin portion of the layer at the beginning of growth (pre-anneal step), and increasing the growth temperature, both result in a larger percent of MnSb2Te4 for similar Mn flux fractions during growth. Samples having at least a few percent of MnSb2Te4 layers exhibit ferromagnetic behavior likely due to the excess Mn in the system which stabilizes on Sb sites as MnSb antisite defects.