First-principles study of spin-transfer torques in layered systems with noncollinear magnetization

An efficient first-principles method was developed to calculate spin-transfer torques in layered system with noncollinear magnetization. The complete scattering wave function is determined by matching the wave function in the scattering region with the Bloch states in the leads. The spin-transfer torques are obtained with the aid of the scattering wave function. We applied our method to the ferromagnetic spin valve and found that the material (Co, Ni, and,Ni80Fe20) dependence of the spin-transfer torques could be well understood by the Fermi surfaces. Ni has much longer spin injection penetration length than Co. Interfacial disorder is also considered. It is found that the spin-transfer torques could be enhanced by the interfacial disorder in some system.