Field-induced anisotropy of magnetic susceptibility in rocks

Summary An induced anisotropy of magnetic susceptibility results from the domain alignment which is produced by treating stationary specimens in a strong alternating field. Appreciable domain re-orientation occurs in fields as low as 50 oersteds and the effect must therefore normally be an important part of the process of alternating field demagnetization. Induced anisotropy has been measured in a number of igneous rocks with a range of palaeomagnetic stabilities and in magnetite powders of controlled grain sizes, dispersed in plaster or kaolin specimens which were mechanically deformed to produce instrinsic magnetic anisotropy by grain alignment. The saturation magnitude of the induced anisotropy is not a function of grain size but the saturating field required increases with decreasing grain size. In the larger grains, induced anisotropy is a function of grain orientation.