Proximity effects on magnetic properties of Ni by the adjacent topological insulator

Topological insulator (TI) are a new class of quantum matter that shows a surface state with spin-momentum locking property. While this unique property was intensely investigated by using TI/ferromagnet (FM) structures, modification of magnetic properties of the FM layer by the adjacent TI has not been systematically investigated. In order to investigate the effect of TI layer on the magnetic properties of FM layer, we have chosen a Ni and a Bi₂Se₃ as FM and TI materials, respectively. We have prepared two series of Ni-based structures: one is deposited on Bi₂Se₃, and the other is deposited on ZnSe. Both Bi₂Se₃ and ZnSe layers were grown by molecular beam epitaxy on (111)B GaAs substrate. Bi₂Se₃ and ZnSe layers were mounted in an e-beam evaporator chamber at the same time, and the Ni films were deposited. The magnetization measured at 5 K with an in-plane magnetic field revealed that a coercive field of Ni on both films decrease with Ni increasing thickness up to 20 nm, but increasing again for further increase in thickness. However, when the magnetic field was applied in an out-of-plane direction, the coercive field of Ni decreased with increasing thickness in both series of samples. On the other hand, the saturation magnetization of Ni/Bi₂Se₃ was always smaller than Ni/ZnSe.