Ferromagnetism of magnetically doped topological insulators in Cr_xBi_2-xTe₃ thin films

We investigated the effect of magnetic doping on magnetic and transport properties of Bi₂Te₃ thin films. Cr_xBi_2-xTe₃ thin films with x = 0.03, 0.14, and 0.29 were grown epitaxially on mica substrate with low surface roughness (∼0.4 nm). It is found that Cr is an electron acceptor in Bi₂Te₃ and increases the magnetization of Cr_xBi_2-xTe₃. When x = 0.14 and 0.29, ferromagnetism appears in Cr_xBi_2-xTe₃ thin films, where anomalous Hall effect and weak localization of magnetoconductance were observed. The Curie temperature, coercivity, and remnant Hall resistance of thin films increase with increasing Cr concentration. The Arrott-Noakes plot demonstrates that the critical mechanism of the ferromagnetism can be described better with 3D-Heisenberg model than with mean field model. Our work may benefit for the practical applications of magnetic topological insulators in spintronics and magnetoelectric devices.