Separation of paramagnetic and ferrimagnetic anisotropies: A review

Abstract

The magnetic anisotropy of rocks results from the contributions of diamagnetic, paramagnetic, and ferromagnetic (in the broad sense) minerals. This bulk anisotropy of magnetic susceptibility, which can be rapidly measured with modern instruments, generally provides a better understanding of the rock deformation history. Different minerals in a rock can form at different times and also respond to deformation in different manners. Therefore it is useful to separate their respective contributions to the whole rock magnetic fabric. Various techniques available to achieve this separation are presented and compared in this article. The variations of magnetic susceptibility with temperature can be used to selectively characterize the contribution of paramagnetic mineral phases following the Curie‐Weiss law. The measurement of magnetic remanence‐related anisotropy provides an efficient way to characterize the contribution of ferrimagnetic and antiferromagnetic species. Finally, measurement of the magnetic properties at high fields, above the saturation magnetization of ferromagnetic minerals, effectively separates the diamagnetic‐paramagnetic magnetic anisotropy. The recent development of these techniques allows the separation of paramagnetic and ferrimagnetic anisotropies to be performed routinely on most specimens and shows promising potential for future magnetic anisotropy studies.