Resonance spin-transfer torque in ferromagnetic/normal-metal/ferromagnetic spin-valve structure of topological insulators

We theoretically study the spin current and spin-transfer torque generation in a conventional spin- valve hybrid structure of type ferromagnetic/normal metal/ferromagnetic (FM/NM/FM) made of the topological insulator (TI), in which a gate voltage is attached to the normal layer. We demonstrate the penetration of the spin-transfer torque into the right ferromagnetic layer and show that, unlike graphene spin-valve junction, the spin-transfer torque in TI is very sensitive to the chemical potential of the NM region. As an important result, by changing the chemical potential of the NM spacer and magnetization directions, one can control all components of the STT. Interestingly, both the resonance spin current and the resonance spin-transfer torque appear for energies determined from a resonance equation. By increasing the chemical potential of the NM spacer, the amplitude of the STTs decreases while at large chemical potentials of $μ_N$ there are intervals of chemical potential in which both the spin current and the spin-transfer torque become zero. These findings could open new perspectives for applications in spin-transfer torque magnetic random access memory (STT-MRAM) devices based on TI.