magnetic topological insulators with high Curie temperatures*

Magnetic topological insulators such as MnBi₂Te₄ and MnSb₂Te₃ were predicted to show intrinsic axion insulator behavior and quantum anomalous Hall (QAH) effect. While a single layer of the material, a septuple layer (SL), is ferromagnetic (FM), the SLs couple antiferromagnetically when stacked into the bulk, making it difficult to achieve zero field QAH conductance. Studies have shown that Mn/Sb antisites foster FM behavior. We have previously grown (Sb₂Te₃)_x(MnSb₂Te₄)_y by molecular beam epitaxy. High crystalline quality materials with compositions varying between 0 and 100% SLs were achieved. Samples with more than a few %SL are FM. Hall resistance measurements show that most of the samples exhibit a Curie temperature (T_C) of 20-30K. A subset of the samples having 70-80% SLs show a second FM component with T_C values as high as 80K. Preliminary magnetization measurements support the presence of the high T_C component in those samples. Possible mechanisms will be considered based on the variations in the distribution of SLs in the samples that may lead to regions of higher T_C. Variations of the growth conditions that result in more controlled Mn incorporation, and their effect on the resulting magnetic properties will also be presented. (NSF Grant Nos. DMR-2011738 and HRD-2112550)