Do topology and ferromagnetism cooperate at the EuS/Bi2Se3 interface?

We probe the local magnetic properties of interfaces between the insulating ferromagnet EuS and the topological insulator Bi2Se3 using low energy muon spin rotation (LE-μSR). We compare these to the interface between EuS and the topologically trivial metal, titanium. Below the magnetic transition of EuS, we detect strong local magnetic fields which extend several nm into the adjacent layer and cause a complete depolarization of the muons. However, in both Bi2Se3 and titanium we measure similar local magnetic fields, implying that their origin is mostly independent of the topological properties of the interface electronic states. In addition, we use resonant soft x-ray angle resolved photoemission spectroscopy (SX-ARPES) to probe the electronic band structure at the interface between EuS and Bi2Se3. By tuning the photon energy to the Eu antiresonance at the Eu M5 pre-edge we are able to detect the Bi2Se3 conduction band, through a protective Al2O3 capping layer and the EuS layer. Moreover, we observe a signature of an interface-induced modification of the buried Bi2Se3 wave functions and/or the presence of interface states.