Computation of Torques in Magnetic Tunnel Junctions through Spin and Charge Transport Modeling

Spin-transfer torque based devices are among the most promising candidates for emerging nonvolatile memory. Reliable simulation tools can help understand and improve the design of such devices. In this paper, we extend the drift-diffusion approach for coupled spin and charge transport, commonly applied to determine the torque in metallic valves, to the case of magnetic tunnel junctions, which constitute the cell of modern spin-transfer torque memories. We demonstrate that, by introducing a magnetization dependent conductivity and properly choosing the spin diffusion coefficient in the tunnel barrier, the expected behavior of both, the electric current and the spin accumulation, is properly reproduced. The spin torque values' dependence on the system parameters is investigated. As a unique set of equations is used for the entire memory cell, this constitutes the basis of an efficient finite element based approach to rigorously describe the magnetization dynamics in emerging spin-transfer torque memories.