spinordning

Spinordning is the spatial arrangement of magnetic moments in a material, reflecting the collective orientation of electron spins that arises from exchange interactions. It is a form of magnetic order that typically develops below a characteristic temperature and can be long-range or short-range.

Common types include ferromagnetic order, where spins align parallel and produce a net magnetization; antiferromagnetic order, where neighboring spins align antiparallel leading to zero net magnetization; ferrimagnetic order, where opposing spins are unequal, yielding a reduced net moment. Non-collinear or spiral spin order occurs when spins rotate gradually across the lattice, as in spin-spiral or helical structures; incommensurate spin-density waves also fall into this class.

Spin order is described by order parameters: the net magnetization for ferromagnets, or the staggered magnetization for antiferromagnets. Long-range order means correlations persist over macroscopic distances, while short-range order vanishes beyond a finite scale. Transitions to spin-ordered states occur at Curie or Néel temperatures and may be continuous or discontinuous.

Experimentally, spinordning is probed by neutron scattering, which reveals Bragg peaks from periodic spin structures, as well as by magnetic susceptibility, X-ray magnetic scattering, and muon spin rotation. Theoretically, it is described by spin models such as the Heisenberg or Ising models, with exchange interactions (direct, superexchange, RKKY) setting the favored order. Spin waves or magnons are low-energy excitations of ordered states.

Spinordning is central to the study of magnetism and materials science, including multiferroics and spintronics, where the control of spin structure enables novel functionalities. Disordered spin systems can form spin glasses, lacking long-range order.