Sahoo, M.; Rahn, M.C.; Kochetkova, E.; Renier, O.; Folkers, L.C.; Tcakaev, A.; Amigó, M.L.; Stier, F.M.; Pomjakushin, V.; Srowik, K.; Zabolotnyy, V.B.; Weschke, E.; Hinkov, V.; Alfonsov, A.; Kataev, V.; Büchner, B.; Wolter, A.U.B.; Facio, J.I.; Corredor, L.T.; Isaeva, A.: Tuning strategy for Curie-temperature enhancement in the van der Waals magnet Mn1+xSb2-xTe4. Materials Today Physics 38 (2023), p. 101265/1-13
10.1016/j.mtphys.2023.101265
Abstract:
The van-der-Waals antiferromagnetic topological insulator MnBi2Te4 is one of the few materials that realize the sought-after quantum anomalous Hall (QAH) state and quantized surface charge transport. To assess the relevance of its isostructural analog MnSb2Te4 as a potential QAH candidate, the roles of Mn/Sb site mixing and cationic vacancies need to be clarified. Recent findings have shown that non-stoichiometry in Mn1±xSb2∓xTe4 is an efficient tuning knob to achieve a net spin-polarized state and to raise the magnetic ordering temperature well above that of MnBi2Te4. Here, we report the crystal structure, the bulk and the surface magnetism of two new Mn1+xSb2−xTe4 samples: Mn1.08Sb1.92Te4(x ≈ 0.1) with TC = 44 K, and Mn2.01Sb1.19Te4(x ≈ 1.0) with the record TC = 58 K. We quantify the site mixing comprehensively by combining various structural probes on powders and single crystals, and then employ bulk, local (electron spin resonance), and spectroscopic (x-ray magnetic circular dichroism) probes to connect these insights to the magnetism of these materials. We demonstrate that Mn over-stoichiometry up to x = 1.0, in combination with a particular Mn/Sb intermixing pattern and the increasingly three-dimensional character of the magnetic order, push the TC upwards. The tendency towards more robust ferromagnetism mediated by stronger interlayer exchange in Mn1+xSb2−xTe4 upon increasing x is confirmed by bulk magnetometry and by a series of density-functional-theory calculations of model structures with varying intermixing.