The spin-orbit interaction is popular for spintronic applications since, through the mechanism of spin-dependent asymmetric scattering, spin currents are generated from charge currents (spin Hall effect) or charge currents are generated from spin currents (inverse spin Hall effect). The discovery of spin, a century ago, relied on a magnetic field gradient to separate opposite spins; this mechanism has received scant attention as a means for generating spin and charge currents in semiconductors. Through the derivation of a set of coupled spin-charge drift-diffusion equations, our paper shows that magnetic field gradients can be used to generate charge currents from nonequilibrium spin polarization in confined solid state systems. We predict, in GaAs, a longitudinal “Stern-Gerlach” voltage. Nonintuitively, we find the spin diffusion length is reduced by the magnetic gradient, which has ramifications for interpreting spin transport experiments. This suppression is understood by invoking the idea of cocurrent and countercurrent exchange, which is a concept found in fields as disparate as animal physiology and thermal engineering.

• Received 27 June 2023
• Revised 30 April 2024
• Accepted 1 May 2024

DOI:https://doi.org/10.1103/PhysRevB.109.195423