Spinresisties

Spinresisties, in the context of spintronics, describe the opposition that a material or an interface offers to the flow of spin current rather than to charge current. They quantify how readily a material can sustain a non-equilibrium spin accumulation, a key concept for understanding how spins are injected, transported, and detected in devices.

The theoretical framework for spinresisties is the diffusive model of spin transport. In a conductor, spin accumulation mu_s decays with distance over a characteristic spin diffusion length lambda. The spin current j_s is driven by gradients in mu_s, and the ratio between spin current and spin accumulation defines a spin resistance. In simple terms, a material segment with resistivity rho and spin diffusion length lambda has a characteristic spin resistance on the order of R_s ~ rho lambda / A, where A is the cross-sectional area. At interfaces between different materials, especially between ferromagnets and nonmagnetic metals, additional spin-dependent interfacial resistances contribute. The complete description is provided by models such as the two-current or Valet-Fert theory, which account for spin polarization and spin relaxation both in bulk and at interfaces.

In devices, spinresisties determine the strength of spin accumulation and the efficiency of spin injection and detection. Nonlocal spin valve geometries maximize the role of the nonmagnetic region’s spin resistance, allowing measurement of the spin diffusion length and polarization. A common experimental metric is the spin resistance area product (RsA), used to compare devices of different sizes.

The concept underpins much of modern spintronics and traces to the diffusion-based framework established in the Valet-Fert model of the 1990s.