Magnetisationen

Magnetisationen are a set of properties that describe the density and orientation of magnetic moments within a material. They are usually represented by the vector M, interpreted as the magnetic moment per unit volume. In SI units, the magnetic induction B is related to the external field H and the magnetisation by B = μ0(H + M), where μ0 is the vacuum permeability.

The magnetisation of a material originates from the intrinsic angular momentum (spin) and orbital motion of electrons. In many materials, exchange interactions cause neighboring moments to align, leading to magnetic order. Ferromagnetic order, for example, produces a spontaneous magnetisation below the Curie temperature. In such materials, the magnetisation is organized into magnetic domains, whose walls shift in response to external fields to minimize energy; under a strong field these domains may align and the material reaches saturation.

Magnetisationen depend on the type of magnetic order. Ferromagnets exhibit a large, spontaneous M; ferrimagnets have net moments due to unequal opposing sublattices; antiferromagnets have nearly cancelling moments; paramagnets show only a temporary alignment in an applied field with small susceptibility; diamagnets develop a weak, opposite response to the field. Real materials also display magnetic anisotropy, which makes magnetisation easier along certain directions, and hysteresis, where M and the internal field follow a loop when the field is cycled.

Key quantities include saturation magnetisation M_s, remanent magnetisation M_r, and coercive field H_c. Magnetisation en masse influences the behavior of magnetic storage media, permanent magnets, electric motors, transformers, and various sensing technologies.