Spinflödet

Spinflödet, or spin flow, refers to the transport of spin angular momentum in solid-state systems, occurring with or without accompanying charge transport. It includes both diffusive spin currents carried by electrons and magnonic spin currents in magnetic insulators. Spinflödet is a central concept in spintronics, where the manipulation of spin transport enables new forms of information processing and storage.

In continuum descriptions, the spin current density j_s represents the flow of spin per unit area per unit time. The spin continuity equation ∂t s + ∇·j_s = τ captures spin relaxation and torques from spin-orbit coupling and magnetic exchange, noting that spin is not strictly conserved in materials with strong spin–orbit interaction. The spin-diffusion length l_sf sets the characteristic distance over which spin polarization decays.

Spin currents can arise from electrical injection, the spin Hall effect—where charge currents generate transverse spin currents—and thermal effects such as the spin Seebeck effect. In insulating magnets, magnons can carry spin currents without charge motion, known as magnonic spin transport.

Experimentally, spinflödet is detected by methods such as the inverse spin Hall effect, non-local spin valve measurements, and spin-pumping experiments conducted at ferromagnet/normal-metal interfaces. The interplay of spin and lattice degrees of freedom leads to rich physics at nanoscales.

Applications of spinflödet include spintronic memory (MRAM), low-power logic devices, magnetic sensors, and magnonic circuits that use spin waves for information processing. Ongoing research aims to understand and optimize spin transport across materials, interfaces, and devices.

The term is used in Swedish and international literature; in English, “spin current” or “spin flow” describe the same physics. Spinflödet intersects with broader topics in spintronics and condensed matter physics, including spin-orbit coupling and topological materials.