Crystal structure and magnetism in layered Mn-Sb-Te and Mn-Ge-Sb-Te tellurides Effects of stoichiometry and site intermixing

This doctoral thesis investigates the crystal structure, phase formation, and magnetic properties of Mn–Sb and Mn–Ge–Sb tellurides, which are structurally related to the magnetic topological insulator MnBi₂Te₄. Improving magnetic ordering in these materials remains a key challenge for their application in quantum technologies, motivating a systematic study of compositional variation and cation intermixing.
The parent compound MnSb₂Te₄ is examined with respect to synthesis conditions and Mn/Sb cation intermixing. Its magnetic properties are highly sensitive to both factors, with ferrimagnetic ordering temperatures ranging from 27 to 46 K depending on Mn content and cation distribution.
The influence of Mn enrichment and cation intermixing in the Mn–Sb–Te family is then addressed. Increasing Mn content leads to new Mn-rich layered phases, including Mn_2.01Sb_1.19Te4 and Mn_1.90Sb_1.39Te4. These phases exhibit enhanced ferrimagnetic ordering temperatures up to 73 K, attributed to partial Mn occupation of the van der Waals gap.
In addition, the Mn–Ge–Sb–Te system is examined. Under certain conditions, phase separation into MnSb₂Te₄-like and GeSb₂Te₄-like structures occurs. A new Mn-rich cubic phase, Mn_0.56Ge_0.09Sb_0.23Te, is identified, showing antiferromagnetic ordering below 24 K.
In conclusion, chemical tuning in Mn–Sb and Mn–Ge–Sb tellurides enables distinct pathways beyond MnSb₂Te₄, leading to both Mn-rich layered ferrimagnets with enhanced ordering temperatures and a new three-dimensional cubic quaternary phase with low-temperature antiferromagnetic order. These findings establish cation intermixing as a key tool for controlling magnetic ground states in related materials.