Unconventional Proximity Driven Exchange Coupling Effects in Topological Insulator/ Ferromagnetic Insulator Bilayers

Experimental observations of emergent electronic states as a result of breaking time reversal symmetry in topological insulators (TIs)/ferromagnetic insulator (FI) bilayers are crucial to understand proximity driven effects in these systems. Often, the interface magnetic behavior is more robust than that of the adjoining FI as demonstrated in Bi2Se3/EuS [Nature 533, 516 (2016)]. We report unusual magneto-transport behavior in Bi2Te3/EuS bilayer; the exchange coupled system displays anisotropic effects through planar Hall effect (PHE) and anisotropic magnetoresistance (AMR) observations. The behavior of the charge carriers at respective magnetic field and temperature regimes reflect the above two effects, each dominating at different regimes. At magnetic field > 1 kOe we find that the PHE dominates and persists up to 200 K, while the AMR effect is only below 4 K and magnetic field < 250 Oe. The representative hysteresis loops are unconventional with symmetric hysteresis loops on either side of B=0 and exhibit topological features; which might be an interplay of spin-orbit coupling and exchange coupling effects; canted moments at the interface with respect to tilt of the Dirac cone.