Magnetic anisotropy of hematite natural crystals: increasing low-field strength experiments |
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| Authors: | S Guerrero-Suarez F Martín-Hernández |
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| Institution: | 1.Dep. Geofísica, Fac. CC. Físicas,Universidad Complutense de Madrid,Madrid,Spain;2.Instituto de Geociencias (UCM-CSIC), Fac. CC. Físicas,Universidad Complutense de Madrid,Madrid,Spain |
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| Abstract: | Hematite is a very abundant mineral in natural rock samples. Despite being one of the most important carriers of remanent
magnetization, its magnetic anisotropy is not well understood partially due to its high coercivity and complex behavior. In
particular, the field intensity beyond which the Rayleigh relation no longer holds varies from one crystal to another. This
field threshold is usually less than the field used in most commercial instruments. The nonlinear behavior of low-field susceptibility
may thus hinder the magnetic fabric analysis. We have carried out an intensive study of the low-field bulk susceptibility
and anisotropy of magnetic susceptibility (AMS) at increasing low fields in the range of 2–450 A/m (effective value) in a
collection of hematite natural crystals. Standard rock magnetic properties, X-ray diffraction, and mass spectrometry have
also been determined in order to discover the parameters influencing the low-field susceptibility variations with field. The
AMS principal directions, the shape of the AMS ellipsoid, and the degree of anisotropy are the parameters that can vary with
different applied fields. It has been found that there is no correlation between magnetic properties like coercivity or saturation
magnetization and the range in which the Rayleigh approximation is valid. However, there seems to be a correlation with the
peak width determined from X-ray diffraction, suggesting that the Rayleigh region in hematite crystals is related to the spatial
orientation of the physical domains within the basal plane. |
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