Investigating the temperature dependent electronic and magnetic properties of ferromagnetic topological insulators (Cr_xSb_1-x)₂Te₃

We have investigated the bulk Cr 3d electronic and magnetic properties of ferromagnetic topological insulators (Cr_xSb_1-x)₂Te₃ by using soft x-ray absorption spectroscopy (XAS) and x-ray circular magnetic dichroism (XMCD). (Cr_xSb_1-x)₂Te₃ exhibits a relatively high Curie temperature with Tc ~100 K and ~200 K for Cr concentration x ~0.15 and x ~0.35, respectively. We have carried out temperature (T) dependent (25 K - 300 K) Cr L-edge XAS and XMCD measurements which show systematic changes and an unconventional T-dependent leading edge shift across Tc, associated with a magnetic gap opening in the unoccupied Cr 3d bulk states. The XMCD signal and magnetic gap as a function of T follow a power-law behaviour, consistent with bulk magnetization experiments and mean-field theory results. Full-multiplet charge transfer cluster model simulations of the Cr L-edge XAS and XMCD spectra are in good agreement with the experiment and indicate (Cr_xSb_1-x)₂Te₃ is a negative charge transfer system.