On the origin of apparently negative minimum susceptibility of hematite single crystals calculated from low-field anisotropy of magnetic susceptibility

0546387 - GLÚ 2022 RIV GB eng J - Journal Article
Hrouda, F. - Ježek, J. - Chadima, Martin
On the origin of apparently negative minimum susceptibility of hematite single crystals calculated from low-field anisotropy of magnetic susceptibility.
Geophysical Journal International. Roč. 224, č. 3 (2021), s. 1905-1917. ISSN 0956-540X. E-ISSN 1365-246X
Institutional support: RVO:67985831
Keywords : Magnetic properties * Magnetic fabrics and anisotropy * Magnetic mineralogy and petrology * Rock and mineral magnetism
OECD category: Condensed matter physics (including formerly solid state physics, supercond.)
Impact factor: 3.352, year: 2021
Method of publishing: Limited access
https://academic.oup.com/gji/article-abstract/224/3/1905/5989708

As shown in the literature several times, the calculation of the anisotropy of magnetic susceptibility (AMS) of hematite single crystals using standard linear AMS theory reveals that the calculated minimum principal susceptibility is parallel to the crystallographic c-axis, but is negative, which is however not due to diamagnetism as evidenced by direct measurements of susceptibility along the principal directions. Susceptibility of a few hematite single crystals from Minas Gerais, Brazil, was measured in 320 directions using a special 3-D rotator and the measurements were processed through AMS calculation by means of standard linear theory and through constructing contour diagrams in equal-area projection. In addition, the susceptibility was in detail measured in three perpendicular planes approximately passing through the main crystallographic directions. The crystals show extremely high anisotropy, the susceptibility measured along the basal plane is several hundred times higher than that along the c-axis and the AMS ellipsoids are very oblate. The contour diagrams show relatively simple patterns of directional susceptibilities, similar to those of the second-rank tensor. Fitting tensor to measured hematite grains results in small but negative minimum principal susceptibility. Nevertheless, summation ofmany oriented grains filters out the non-tensorial parts of the grain susceptibility in multicrystal assemblages, the AMS of which is well represented by a tensor.
Permanent Link: http://hdl.handle.net/11104/0322918