SL/QL sequences*

Recent predicted intrinsic magnetic topological materials in the MB₂T₄-family (where M = V, Mn, Ni or Eu, B = Bi or Sb, T = Te, Se, or S) show a great promise for realizing intrinsic axion insulators and quantum anomalous Hall (QAH) insulators. These materials modify the B₂T₃ crystal structure forming septuple layers (SL) in the form of T-B-T-M-T-B-T. Not all of the listed magnetic TI candidates have been yet explored, and thus far out-of-plane surface magnetization was only found in MnBi₂Te₄ and MnSb₂Te₄. Both materials are antiferromagnetic (AFM) in the bulk and not suitable for QAH unless they have odd number of SLs. Recent studies in MnBi₂Te₄ have shown that separating SLs with Bi₂Te₃ quintuple layers (QL) turns an AFM into a ferromagnet (FM). Here we show that through layer-by-layer growth using molecular beam epitaxy (MBE) we can control the SL/QL sequence. We describe the conditions for which MnSb₂Te₄/Sb₂Te₃ sequence is ferromagnetic with T_c higher than that in the Bi-based SL/QL sequence, as witnessed by large anomalous Hall signal with coercive field ~0.1 T at 2 K. The structural (TEM and HR-XRD) characterization and the optimization of the SL/QL sequence will be presented.