High-temperature ferromagnetic topological crystalline insulating state induced by proximity effect in a EuS/SnTe heterostructure*

Ferromagnetic topological insulators attract much attention because they enable us to realize the quantum anomalous Hall effect (QAHE), possibly useful for low-energy-consumption devices by using the chiral edge state. However, the temperature for QAHE is still low mostly due to degradation of crystallinity by doping magnetic atoms. To prevent it, using ferromagnetic proximity effect is one of the solutions [1,2]. We made and measured a EuS/SnTe heterostructure. As a result, intriguingly, the perpendicular magnetization (PM) reaches minimum at ~100 K and then increases with increasing temperature and keeps up to room temperature. A similar behavior was reported in EuS/Bi₂Se₃[1], and the explanation is that after disappearance of bulk magnetization in EuS (T_C=17 K), the direction of the interface magnetization becomes perpendicular from oblique with increasing temperature. On the other hand, when we use a trivial insulator PbTe: EuS/PbTe, the PM monotonically decreases with increasing temperature. This suggests that the anomalous interface ferromagnetism is induced by the non-trivial nature in SnTe. [1] F. Katmis et al., nature 533, 513 (2016). [2] R. Akiyama et al., arXiv 1910.10540 (2019).