Abstract

Ferromagnetic exchange in magnetically-doped topological insulators (TI) can break time-reversal symmetry and open a gap in the quasiparticle Dirac spectrum of the two-dimensional surface states. The quantum anomalous Hall (QAH) effect can be observed when the Fermi level is inside the exchange gap [1-2]. In addition, tuning the Fermi level out of the exchange gap repopulates the surfaces, resulting in changes in temperature with magnetization that can be considerable at millikelvin temperatures [3]. We study this magnetocaloric effect by performing magnetization loops while simultaneously monitoring the resistance and temperature of the (Bi0.29Sb0.71)1.89V0.11Te3 films. We find that sweeping the external magnetic field beyond the coercive field of the film and then back to zero field lowers the sample temperature. The possible origin of the cooling is the magnetocaloric effect from the film. In the demagnetization process the film can reach a temperature below the base temperature of the dilution refrigerator.