Spin-current drift–diffusion transport in common spin–orbit-torque structures

Abstract

We summarize and simplify the drift–diffusion transport of spin-currents in s-band dominant transition metal systems for a few well-studied one dimensional solutions for technology-relevant measurements. They highlight the importance of the spin-current “loading” effect and interface spin resistance-area products (spin-RAs). Main conclusions from this study are (1) For a nonmagnetic conduction metal, there is a material-specific spin-RA that is defined by (ρ×λsf), i.e., the resistivity-spin flip 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 material specific metrics, such as ΘSH and λsf from observations, while including the role of interface spin-RAs. (3) Such interface-related spin-RA consideration exists also for common ferromagnetic transition metal/alloys, which combines spin-flip scattering with that of transverse spin-dephasing (mixing-conductance) related spin-currents and generally making an interface spin-conductance that is non-isotropic against spin-current’s polarization direction. Finally, these spin-RAs present a very low impedance environment of the order of 1mΩ μm2, in contrast with common structures in CMOS technology where RAs are usually above 1Ω μm2, such as a magnetic tunnel junction in CMOS-integrated magnetic memory. The low impedance nature of spin-current drift–diffusion transport is important to consider for accurate measurements and for technology integration.