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Field‐impressed magnetic anisotropy in rocks
Author(s) -
Potter David K.,
Stephenson Alan
Publication year - 1990
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl017i013p02437
Subject(s) - anisotropy , remanence , ferrimagnetism , demagnetizing field , rock magnetism , geology , magnetite , condensed matter physics , single domain , magnetic anisotropy , field (mathematics) , magnetic domain , magnetic field , natural remanent magnetization , magnetic susceptibility , magnetization , mineralogy , materials science , geophysics , physics , optics , paleontology , mathematics , quantum mechanics , pure mathematics
The application of alternating (AF) or direct (DF) magnetic fields to two weakly anisotropic rock specimens which remain static, significantly alters their measured low‐field anisotropy of magnetic susceptibility (AMS) by superimposing an anisotropy which has the form of an ellipsoid of revolution with its unique axis aligned along the field axis. Previous AF history is also shown to influence the acquisition of isothermal remanent magnetization (IRM). These effects can be quite substantial and thus it is essential that rocks should not be used for low‐field AMS analysis or for IRM anisotropy studies if they have previously been subjected to static AF demagnetization. AMS studies should also not be carried out on rocks which carry a significant remanence (e.g., an IRM acquired in ≥5 mT). The field‐impressed effects were also strongly dependent upon whether the ferrimagnetic particles in the rocks were predominantly multidomain (MD) or uniaxial single‐domain (SD). The results were consistent with our recent work on synthetic specimens (containing magnetite, titanomagnetite or magnemite) and add support to our suggestion that these effects could provide a rapid, nondestructive, means of determining the predominant domain state (MD or uniaxial SD) of ferrimagnetic particles in rocks.