Spinordningarna

Spinordningar are the spatial arrangements of electron spins in a material that constitute an ordered phase of the spin degree of freedom. They arise from exchange interactions between magnetic moments and are characterized by an order parameter that is nonzero below a critical temperature. In ferromagnets, spins align parallel, yielding a net magnetization. In antiferromagnets, neighboring spins align antiparallel, giving zero net magnetization but nonzero staggered magnetization. Ferrimagnets have unequal opposite moments producing a net moment. More complex forms include spiral or helical order, where the spin direction rotates with position; spin-density waves, where the magnitude and/or phase of the spin density modulates periodically; and chiral spin textures such as skyrmion lattices in certain non-centrosymmetric magnets. Spinordningar can also be frustrated, leading to spin glasses with frozen disorder or quantum spin liquids with strong fluctuations.

The onset of spin order is marked by ordering temperatures: Curie temperature for ferromagnets, Néel temperature for many antiferromagnets. Theoretical treatments use exchange constants, anisotropy and external fields; order parameters and symmetry breaking describe phase transitions. Experimental probes include neutron scattering, which directly maps spin correlations, magnetization measurements, muon spin rotation, and X-ray magnetic scattering.

Spinordningar occur in a wide range of materials, from transition-metal oxides and rare-earth compounds to helimagnets and itinerant magnets. They underpin phenomena such as magnetization, magnetoresistance and spintronic effects.