Reproducibility of high field magnetic remanence: Implications for precision of high field remanence anisotropy

It was shown in the earlier model studies that the precision in the determination of the anisotropy of magnetic susceptibility (AMS) depends in a directly proportional way on the precision of the measurement of the directional susceptibility in relation to the degree of anisotropy. These results can be closely applied to the measurement of the anisotropy of magnetic remanence (AMR).

While the AMR imparted in weak to moderate fields is relatively frequently used in rock fabric studies, only a few attempts to establish the anisotropy of magnetic remanence imparted in high fields (HFRA) were reported. The reasons for the virtual absence of the HFRA studies may be both instrumental (insufficient precision in setting up the intensity of magnetizing field, insufficiently homogeneous magnetizing field) and methodological (time variation of imparted remanence, unknown properties of high field remanence).

Recently, an impulse magnetizer was developed (commercial name PUMA) that enables the standard palaeomagnetic specimen to be magnetized in a defined orientation in the wide range of magnetic fields from 1 mT to 5 T. Elaborate design of the instrument provides precise setting of the pulse intensity as well as high homogeneity of the field over entire specimen volume. In addition, reproducibility in imparting the remanence in the same direction by the same field was investigated as well as it was investigated whether it is desirable to demagnetize the specimen between individual magnetizations to improve the remanence reproducibility despite that each high field magnetization (“saturation”) theoretically obliterates the previous remanence. The investigations were made on specimens having single mineral ferromagnetic fraction (magnetite, hematite and pyrrhotite ones). The results help us to decide whether the HFRA is convenient to most rocks or only to strongly magnetic and strongly anisotropic ones.