The Magnetocaloric Effect in Magnetic Topological Insulators

Ferromagnetic exchange in magnetically-doped topological insulators (TIs) can break time-reversal symmetry and open a gap in the quasiparticle Dirac spectrum of the two-dimensional surface states^[1-2]. 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 (Bi_0.29Sb_0.71)_1.89V_0.11Te₃ films. We find that sweeping the external magnetic field beyond the coercive field and back to zero field lowers the sample temperature, while magnetization reversal around zero field results in a prominent heating effect. We rule out the influence of eddy current heating and show that the possible origin of the heating and cooling is the magnetocaloric effect from the film. In the demagnetization process we demonstrate that the film can reach a temperature below the base temperature of the dilution refrigerator.