Direct and indirect spin current generation and spin-orbit torques in ferromagnet/nonmagnet/ferromagnet trilayers
Year: 2024
Type: article
Abstract: Spin-orbit torques in ferromagnet/nonmagnet/ferromagnet trilayers are studied using a combination of symmetry analysis, circuit theory, semiclassical simulations, and first-principles calculations using the nonequilibrium Green's function method with supercell disorder averaging. We focus on unconventional processes involving the interplay between the two ferromagnetic layers, which are classified into direct and indirect mechanisms. The direct mechanism involves spin current generation by one ferromagnetic layer and its subsequent absorption by the other. In the indirect mechanism, the in-plane spin-polarized current from one ferromagnetic layer ``leaks'' into the other layer, where it is converted into an out-of-plane spin current and reabsorbed by the original layer. The direct mechanism results in a predominantly dampinglike torque, which damps the magnetization towards a certain direction ${\mathbf{s}}_{d}^{}$. The indirect mechanism results in a predominantly fieldlike torque with respect to a generally different direction ${\mathbf{s}}_{f}^{}$. Similarly to the current-in-plane giant magnetoresistance, the indirect mechanism is only active if the thickness of the nonmagnetic spacer is smaller than or comparable to the mean free path. Numerical calculations for a semiclassical model based on the Boltzmann equation confirm the presence of both direct and indirect mechanisms of spin current generation. First-principles calculations reveal sizable unconventional spin-orbit torques in Co/Cu/Co, Py/Cu/Py, and Co/Pt/Co trilayers and provide strong evidence of indirect spin current generation.
Institutions: Indiana University, University of Nebraska–Lincoln
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Awards: G1605636979, First-Principles Studies of Spin-Orbit Torque and Magnetoresistance in Magnetic Nanostructures, DMREF: GOALI: Designing Materials for Next-generation Spintronic Devices, SPIN CURRENTS IN MAGNETIC SYSTEMS AND HETEROSTRUCTURES, SPIN CURRENTS IN MAGNETIC SYSTEMS AND HETEROSTRUCTURES, Collaborative Research: Spin Currents and Spin-orbit Torques in Single Layer Magnetic Systems, G7656102289
OpenAlex ID: W4405533378