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Anisotropy of susceptibility in rocks which are magnetically nonlinear even in low fields
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SYSNO ASEP 0490845 Document Type J - Journal Article R&D Document Type Journal Article Subsidiary J Článek ve WOS Title Anisotropy of susceptibility in rocks which are magnetically nonlinear even in low fields Author(s) Hrouda, F. (CZ)
Chadima, Martin (GLU-S) RID, SAI
Ježek, J. (CZ)Source Title Geophysical Journal International - ISSN 0956-540X
Roč. 213, č. 3 (2018), s. 1792-1803Number of pages 12 s. Publication form Print - P Language eng - English Country GB - United Kingdom Keywords electrical properties ; magnetic properties ; magnetic fabrics and anisotropy ; magnetic mineralogy and petrology ; rock and mineral magnetism Subject RIV DE - Earth Magnetism, Geodesy, Geography OECD category Geology R&D Projects IAAX00130801 GA AV ČR - Academy of Sciences of the Czech Republic (AV ČR) Institutional support GLU-S - RVO:67985831 UT WOS 000434675800026 EID SCOPUS 85052515577 DOI 10.1093/gji/ggy088 Annotation Theory of the low-field anisotropy of magnetic susceptibility (AMS) assumes a linear relationship between magnetization and magnetizing field, resulting in field-independent susceptibility. This is valid for diamagnetic and paramagnetic minerals by definition and also for pure magnetite, while in titanomagnetite, pyrrhotite and hematite the susceptibility may be clearly field-dependent even in low fields used in common AMS meter. Consequently, the use of the linear AMS theory is fully legitimate in the former minerals, but in principle incorrect in the latter ones. Automated measurement of susceptibility in 320 directions in variable low-fields ranging from 5 to 700 A m-1 was applied to more than 100 specimens of various pyrrhotite-bearing and titanomagnetite-bearing rocks. Data analysis showed that the anisotropic susceptibility remains well represented by an ellipsoid in the entire low-field span even though the ellipsoid increases its volume and eccentricity. The principal directions do not change their orientations with low-field in most specimens. Expressions for susceptibility as a function of field were found in the form of diagonal tensor whose elements are polynomials of low order. In a large proportion of samples, the susceptibility expressions can be further simplified to have one common skeleton polynomial. Workplace Institute of Geology Contact Jana Popelková, popelkova@gli.cas.cz, Sabina Janíčková, Tel.: 233 087 272 Year of Publishing 2019
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