Developments in rock magnetism

Rock magnetism is concerned with the remanent magnetisation of ferrimagnetic fine particles in weak fields ( approximately=0.1 mT), at temperatures ranging from ambient to the Curie point, and over times of geological length. Since most magnetisations in rocks or their synthetic analogues are thermally activated, the blocking temperature below which the approach to equilibrium is effectively frozen is of particular importance. The author summarises current thinking about thermally activated magnetic processes, and puts them in the context of recent discoveries about magnetic domain structure in crystals containing only one or a few domains. Pseudo-single-domain effects in such crystals, which bridge the gap between classic single-domain and multidomain behaviour, are one of the current frontiers in rock magnetism.