spinaccumulation

Spin accumulation (sometimes written spinaccumulation) is a non-equilibrium excess of electronic spin polarization that develops in a conductor or at an interface when spin-up and spin-down populations are driven out of balance. It is a central concept in spintronics, describing a local difference in spin-dependent chemical potentials (often denoted μs = μ↑ − μ↓) that can diffuse, relax, and produce measurable voltages or torques.

Spin accumulation can be generated by spin injection from a ferromagnet, by the spin Hall effect or Rashba–Edelstein effect in materials with strong spin–orbit coupling, by spin pumping from ferromagnetic resonance, or by thermal gradients (spin Seebeck effect). The spatial behavior is governed by spin diffusion and relaxation; in the simplest steady-state model the spin chemical potential decays over the spin diffusion length λs, set by the spin relaxation time and carrier mobility.

Consequences of spin accumulation include modifications of local resistance (magnetoresistance effects), generation of spin-transfer or spin–orbit torques on nearby magnets, and conversion into electric signals via the inverse spin Hall effect. It is quantified and modeled using spin-resolved transport equations and material-specific parameters such as spin diffusion length, polarization, and interfacial spin-mixing conductance.

Experimental detection methods include nonlocal spin-valve measurements, spin-polarized tunneling, optical Kerr rotation, ferromagnetic resonance spin pumping, and inverse spin Hall voltage measurements. Spin accumulation underpins device concepts for memory, logic, and sensors that exploit spin currents and provides a link between microscopic scattering processes and macroscopic spin transport phenomena.