Spin Current Drift-Diffusion Transport in Common Spin-Orbit-Torque Structures

We summarize and simplify the drift-diffusion transport of spin-currents in s-band dominant transition metal systems and examine a few well-studied one dimensional solutions for technologyrelevant measurements. They highlight the importance of the spin-current “loading” effect, and the importance of interface spin resistance-area products (spin-RAs). Main conclusions from this study are (1) For every nonmagnetic (NM) conduction metal, there is a materials-specific spin-RA that is defined by (ρ × λsf ), i.e. the resistivity-spin filp diffusion length product. This spin-RA sets the scale for other interface-related spin-RA quantities for effective spin-current transport. (2) Any spin-Hall coefficient (ΘSH) measurements needs to have a full spin-conductance analysis to ensure the proper deduction of materials specific metrics such as ΘSH and λsf from observations, including the role of interface spin-RAs. (3) This materials-specific spin-flip diffusion related spin- RA exists for common ferromagnetic transition metal/alloys also. It causes an additional spin conductance channel, diverting part of the spin-current, presenting an added correction to non-local spin-current measurements such as from line-width studies of ferromagnetic resonance. Finally, these spin-RAs present a very low impedance environment of the order of 1mΩμm2. This is in contrast with structures in CMOS technology where RAs are usually above 1Ωμm2, such as for a magnetic tunnel junction in CMOS-integrated magnetic memory. This low impedance nature of spin-current drift-diffusion transport is important to consider for accurate measurements and for technology integration.