Magnetic and transport study of magnetic topological insulators

We have successfully synthesized three magnetic topological insulators for our study: Mn₂Bi₂Te₅, MnBi₂Te₄, and MnBi₄Te₇. Till now, thickness-dependent magnetic behavior, Quantum anomalous effect, and Axion insulator state have been observed in MnBi₂Te₄. We obtained a good fit with the reported result from Rietveld's analysis. The percentage of a secondary phase of MnTe was observed, which was below 4% in all cases. From the scanning electron microscopy (SEM) measurement, we have confirmed the layered nature of the samples. Elemental analysis verified that the molar percentage of Mn: Bi: Te was 1: 2.2: 4.07 for MnBi₂Te₄, which is very close to the desired result. For, Mn₂Bi₂Te₅ and MnBi₄Te_7, we got a satisfactory result. From HRTEM and SAED, we deduced the lattice spacing. We micro-mechanically exfoliated the 2D sheets and performed HRTEM. The selected area of electron diffraction gave information regarding all the highly oriented crystals. From the Curie-Weiss fitting of M-T data, we obtained a transition temperature for Mn₂Bi₂Te₅, MnBi₂Te₄, and MnBi₄Te₇ at 11K, 24K, and 13 K (out of plane),  respectively. Differential conductance vs voltage measurements at different temperatures revealed the increment in the conductivity as we lowered the temperature below the transition temperature, which also agreed well with the resistivity vs temperature measurements.