Effects of Crystalline Disorder on Interfacial and Magnetic Properties of Sputtered Topological Insulator/Ferromagnet Heterostructures

Thin films of topological insulators (TIs) coupled with ferromagnets (FMs) are excellent candidates for energy-efficient spintronics devices. Here, the effect of the crystalline structural disorder of TI on the interfacial and magnetic properties of sputter-deposited TI/FM, Bi2Te3/Ni80Fe20, heterostructures is reported. Ni and a smaller amount of Fe from Py were found to diffuse across the interface and react with Bi2Te3. For improved crystalline c-axis-oriented Bi2Te3 films, a significant enhancement in Gilbert damping is observed, accompanied by an effective out-of-plane magnetic anisotropy and enhanced damping-like spin-orbit torque (DL-SOT), possibly due to the topological surface states (TSS) of Bi2Te3. Furthermore, a spontaneous exchange bias is observed in hysteresis loop measurements at low temperatures. This is caused by a topological antiferromagnetic interfacial layer formed due to a solid-state reaction between the diffused Ni with Bi2Te3 that couples with the FM, Ni80Fe20. For the increasing disorder of Bi2Te3, a significant weakening of the exchange interaction in the AFM interfacial layer is observed. These experimental results open the pathway for further exploration of crystalline-disordered TIs and their interfaces.