Evidence for ferromagnetic coupling at the doped topological insulator/ferrimagnetic insulator interface

Abstract

One of the major obstacles of the magnetic topological insulators (TIs) impeding their practical use is the low Curie temperature (T[subscript c] ). Very recently, we have demonstrated the enhancement of the magnetic ordering in Cr-doped Bi₂Se₃ by means of proximity to the high-T[subscript c] ferrimagnetic insulator (FMI) Y₃Fe₅O₁₂ and found a large and rapidly decreasing penetration depth of the proximity effect, suggestive of a different carrier propagation process near the TI surface. Here we further present a study of the interfacial magnetic interaction of this TI/FMI heterostrucutre. The synchrotron-based X-ray magnetic circular dichroism (XMCD) technique was used to probe the nature of the exchange coupling of the Bi[subscript 2-x] Cr [subscript x] Se₃/Y₃Fe₅O₁₂ interface. We found that the Bi[subscript 2-x] Cr [subscript x] Se₃ grown on Y₃Fe₅O₁₂ (111) predominately contains Cr ³⁺ cations, and the spin direction of the Cr³⁺ is aligned parallel to that of tetrahedral Fe³⁺ of the YIG, revealing a ferromagnetic exchange coupling between the Bi [subscript 2-x] Cr [subscript x] Se₃ and the Y₃Fe₅O₁₂.