 Spin accumulation

Spin accumulation is a nonequilibrium imbalance between spin populations, often described by a difference of spin-dependent electrochemical potentials $\delta {\mu }_s={\mu }_{\uparrow }-{\mu }_{\downarrow }$. A spin-polarized injected current can create such an imbalance even in a nonmagnetic conductor. Diffusion spreads it while spin relaxation tends to remove it, defining characteristic time and length scales. A transverse magnetic field makes the spin orientation precess and can change a detector signal, the principle of a Hanle spin-precession measurement. This nonequilibrium population is distinct from equilibrium magnetization or a charge-density accumulation.