Coupled spin and charge drift-diffusion approach applied to magnetic tunnel junctions. (December 2021)

• Record Type: Journal Article
• Authors: Fiorentini, S.; Ender, J.; Selberherr, S.; de Orio, R.L.; Goes, W.; Sverdlov, V.
• Is Part Of: Solid-state electronics. Volume 186(2021)
• Publication Date: 2021-12
• Subjects: Spin and charge drift-diffusion -- Spin-transfer torque -- Magnetic tunnel junctions -- STT-MRAM; Semiconductors -- Periodicals; Semiconducteurs -- Périodiques; 621.38152
• DOI: 10.1016/j.sse.2021.108103
• Languages: English
• ISSNs: 0038-1101

Abstract

Highlights: Spin and charge drift-diffusion equations solved numerically using finite elements. Equations adapted to a magnetic tunnel junction for STT-MRAM torque computation. Tunnel barrier modeled with low conductivity depending on magnetization orientation with tunneling magnetoresistance ratio. Tested spin-transfer torque dependence on system parameters. Reproduced magnitude expected in magnetic tunnel junctions. Abstract: A drift-diffusion approach to coupled spin and charge transport has been commonly applied to determine the spin-transfer torque acting on the magnetization in metallic valves. This approach, however, is not suitable to describe the predominant tunnel transport in magnetic tunnel junctions. In this work we present a coupled Finite Element solution to the spin and charge drift–diffusion equations. We demonstrate that by introducing a magnetization dependent resistivity one can successfully reproduce the resistance dependence on the magnetization orientation in the ferromagnetic layers. We then investigate the dependence of the resulting torques on system parameters, and show that the approach is able to reproduce the torque magnitude expected in a magnetic tunnel junction. As a unique set of equations is used for the entire structure, this constitutes an efficient Finite Element based approach to describe the magnetization dynamics in emerging spin-transfer torque memories.