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

Wenqing Liu,Koichi Murata,Liang He,Yan Zhou,Mehmet C Onbasli,Yongbing Xu,Rong Zhang,Yong Wang,Kang L Wang,Ying Jiang,Caroline A Ross

doi:10.1063/1.4943157

Abstract

One of the major obstacles of the magnetic topological insulators (TIs) impeding their practical use is the low Curie temperature (Tc). Very recently, we have demonstrated the enhancement of the magnetic ordering in Cr-doped Bi2Se3 by means of proximity to the high-Tc 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 Bi2−xCrxSe3/Y3Fe5O12 interface. We found that the Bi2−xCrxSe3 grown on Y3Fe5O12(111) predominately contains Cr3+ 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 Bi2−xCrxSe3 and the Y3Fe5O12.

Highlights

One of the major obstacles of the magnetic topological insulators (TIs) impeding their practical use is the low Curie temperature (Tc)
We have demonstrated the enhancement of the magnetic ordering in Cr-doped Bi2Se3 by means of proximity to the high-Tc 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
Within the growing family of magnetically doped TIs, ferromagnetism has been observed in Cr- and Mn-doped single crystals of Sb2Te3,11–13 Fe- and Mn-doped single crystals of Bi2Te3,14,15 and Mn- and Cr-doped thin films of Bi2Se3.16–18 Apart from transition metals, rare-earth metals such as Gd,[19] Dy, and Sm20 have been explored as an effective dopant to induce long-range magnetic ordering in Bi2Se3 or Bi2Te3.21 Growing TIs on top of ferromagnetic metals (FMs) and insulators (FMIs), or vice versa, has been shown to produce an exchange interaction affecting the SS of TIs