Effects of FM/NM Interfaces on Spin Accumulation in Free Layer of Pseudo-Spin-Valve Structure
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0998-J02-03
Effects of FM/NM Interfaces on Spin Accumulation in Free Layer of Pseudo-Spin-Valve Structure Jiuning Hu, Min Ren, Lei Zhang, Ning Deng, Hao Dong, and Peiyi Chen Institute of Microelectronics, Tsinghua University, Beijing, 100084, China, People's Republic of ABSTRACT The ferromagnetic/nonmagnetic (FM/NM) interfacial effects on the spin accumulation in the free layer were studied in a pseudo-spin-valve structure (PSVs) consisting of two FM layers separated by a NM spacer layer. We developed a spin current model for the current-induced magnetic switching (CIMS) effect based on the spin diffusion equations and appropriate boundary conditions, and derived a new formula for the spin-dependent electrochemical potentials that are related to the spin-dependent density of states. The results indicate that the spin accumulation in the free layer mainly depends on the interfacial spin asymmetry coefficient ξ which originates from the spin-dependent interfacial conductance. In the parallel (anti-parallel) configuration of the magnetization direction for the free and fixed layer, the positive (negative) electron current (electrons from the free layer to the fixed layer and vice versa) drives the spin current polarization factor at the interface between the top electrode and the free layer to vary from ξ (-ξ ) to 0, while at the interface between the free layer and the spacer layer the spin current polarization factor vary from ξ (0) to ξ /2, which means the total spin current polarization factor in the free layer varies from 0 (ξ ) to ξ /2. These results show that the anti-parallel configuration has a less critical switching current than that of the parallel configuration. Thus, we can design PSVs with symmetrical critical current based on the model. INTRODUCTION Since the first theoretical prediction of the CIMS effect by Slonczewski [1] and Berger [2] in 1996, extensive endeavor has been devoted to both the theoretical [3-5] and experimental [6-8] study of the CIMS effect. In most theoretical models, the spin transfer torque carried by the itinerate electrons acting on the magnetization of the FM layer plays a crucial role in the switching mechanism [9-10], which causes the spin accumulation in the free layer. While the electron current density perpendicular to the layers exceeds some threshold, the magnetization reversal of the free layer occurs. Since the relaxation time of the itinerate electrons in the FM layer is far less than the spin relaxation time, the spin accumulation of the itinerate electrons in the free layer adiabatically follows the movement of the magnetization. This physical picture allows us to focus on the spin accumulation in the free layer and demonstrate the CIMS mechanism. The model presented in this work consists of the diffusion equation [11] and resistance boundary conditions [12,13], and it also takes the asymmetry of the DOS and the diffusion constants for the two spin species in the FM layer into account. The arrangement of the paper is organized as follows. In the theory part, the fo
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