Very High Curie temperature (MnSb2Te4)x(Sb2Te3)1-x Magnetic Topological Insulator Structures Grown by Molecular Beam Epitaxy*

Previously, it was shown that we can control the composition (x) of the magnetic topological materials (MnSb2Te4)x(Sb2Te3)1-x by adjusting the Mn flux ratio during MBE growth.1 We learned that Mn incorporates as a structural element to form MnSb2Te4 septuple layers (SL) or as anti-site defects. Samples with 70-80% SLs (x = 0.7-0.8) exhibited Curie temperatures (Tc) as high as 80K. Here we report further enhancement of the Tc by modifying two MBE growth parameters: Mn beam equivalent pressure (BEP) ratios and growth rates (GR). We observed that, for samples with 70 – 80 % SLs, gradually increasing the Mn BEP ratio from 0.04 to 0.09 led to higher Tc values (from 20K to 80K). Furthermore, at very low BEP ratios there was evidence for the coexistence of ferromagnetic and antiferromagnetic phases. This suggests the approach to stoichiometric MnSb2Te4 growth and low Tc values at low Mn contents, while excess substitutional Mn in the structures promoted the higher Tc values. Samples grown at a constant Mn BEP ratio of 0.09 with a reduced GR of 0.5-0.6 nm/min (compared to 0.9-1.0 nm/min used previously) resulted in structures with ~80% SLs that exhibit even higher Tc values of 100K and above. These Tc values are higher than any values reported to date for these materials. EDX analysis suggests significantly increased Mn(Te) and Mn(Sb) substitutions for samples with reduced GR. We will present these results as they relate to the (MnSb2Te4)x(Sb2Te3)1-x structural properties, as well as the details of the proposed growth mechanism.