EGU21-3076
https://doi.org/10.5194/egusphere-egu21-3076
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Unexpectedly strong shape anisotropy of out-of-phase magnetic susceptibility due to eddy currents of internally isotropic copper cylinders

Josef Ježek and František Hrouda
Josef Ježek and František Hrouda
  • Faculty of Science, Charles University, Prague, Czech Republic (josef.jezek@natur.cuni.cz)

In order to better understand the anisotropy of out-of-phase magnetic susceptibility (opAMS) due to eddy currents of rocks and minerals, we investigated the ipAMS and opAMS of copper cylinders, because copper is diamagnetic, internally isotropic magnetically, and its opMS is no doubt due to eddy currents. Results of laboratory measurements were compared to theoretical models.  The degree of AMS (P=k1/k3, k1>k2>k3) of internally isotropic substance is controlled by the internal susceptibility and demagnetizing factors solely controlled by the substance shape. If the internal susceptibility is very low and this is the case of magnetostatic susceptibility of most diamagnetic substances, there is virtually no shape anisotropy of such material. The magnetostatic susceptibility of copper is about -8 x 10-6 [SI units], which gives rise to undetectably low degree of magnetostatic AMS. The ipMS is also negative, but several orders lower depending on grain size, grain shape, and operating frequency. The opMS is on the other hand positive, relatively high and also dependent on operating frequency. Calculated from signed (negative) k1, k2, k3 values, the degree of ipAMS, P<1, and decreases with increasing elongation of copper cylinders. It also depends on grain size and operating frequency. The degree of opAMS, P>1 and increases with increasing cylinder elongation. It also depends on grain size and operating frequency. Parallel to the axes of elongated cylinders are the ipk1 and opk3 directions, while in flattened cylinders are parallel to the cylinder axes the ipk3 and opk1 directions. The above results are useful in the structural interpretation of the opAMS of rocks and ores whose opAMS is due eddy currents (in electrically conductive materials).

How to cite: Ježek, J. and Hrouda, F.: Unexpectedly strong shape anisotropy of out-of-phase magnetic susceptibility due to eddy currents of internally isotropic copper cylinders, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3076, https://doi.org/10.5194/egusphere-egu21-3076, 2021.

Displays

Display file