spinreorientation

Spin reorientation refers to a change in the preferred orientation of the magnetic moments in a material, driven by changes in the balance of magnetic anisotropy terms, external conditions, or structural factors. In many magnets, the direction in which spins align—an easy axis or an easy plane—is set by magnetocrystalline anisotropy and dipolar interactions; when these competing effects shift so that a different direction minimizes the free energy, the system undergoes a spin reorientation transition.

Reorientation can be induced by temperature, applied magnetic field, mechanical strain, or changes in sample geometry (e.g., thickness in thin films). Temperature changes alter anisotropy constants, and can lead to a spin reorientation temperature where the easy axis switches. In antiferromagnets, a field-induced reorientation may occur through a spin-flop transition, which is distinct but closely related.

In thin films and nanostructures, magnetoelastic coupling and shape anisotropy can drive reorientation, yielding a switch from out-of-plane to in-plane magnetization or vice versa. The transition can be gradual (continuous) or abrupt (first order), depending on the material and the interaction strengths.

Experimentally, spin reorientation is detected by magnetization measurements, torque magnetometry, anisotropic magnetoresistance, or neutron diffraction, and is modeled with free-energy expansions including anisotropy terms such as K1, K2, etc.; Landau theory and micromagnetic simulations are common tools.

Spin reorientation phenomena are important in the design of magnetic storage, sensors, and spintronic devices, where control of magnetization direction with external stimuli is desirable.