Spincurrent

Spincurrent, or spin current, refers to the transport of spin angular momentum through a material or across interfaces. It is not identical to electric charge current, though the two can be related: a spin current can carry spin polarization without a net flow of charge (a pure spin current), or it can accompany a charge current when spins are carried by moving electrons with a preferred spin orientation.

In solid-state physics, spin current is described by a spin-current density, a tensor that captures the flux of a spin component in a given spatial direction. A common way to think about it is as the flow of spin polarization: electrons with up or down spin moving through a region transfers angular momentum even if the overall charge movement cancels.

Spin currents can be generated by several mechanisms. Electrical spin injection from a ferromagnet into a nonmagnetic material creates a spin-polarized current, while dynamic methods such as spin pumping use precessing magnetization to emit spin current. The spin Hall effect, and its reciprocal, convert charge currents into transverse spin currents or convert spin currents back into measurable voltages in materials with strong spin–orbit coupling. Optical methods, such as circularly polarized light, can also create or probe spin currents.

Detection and characterization often rely on nonlocal magnetoresistance measurements, spin-torque phenomena, or optical techniques like Kerr rotation. In many materials, the spin diffusion length and spin relaxation times determine how far and how long a spin current can persist before losing polarization.

Spin currents lie at the core of spintronics, with potential applications in memory, logic, and low-power information processing, where manipulation of spin rather than charge aims to reduce energy consumption and increase device functionality.