Changes in mean magnetic susceptibility and its anisotropy of rock samples as a result of alternating field demagnetization

Measurements of low-field magnetic susceptibility (K) and its anisotropy (AMS) on different rock types during stepwise alternating field (AF) demagnetization in increasing fields revealed not only significant changes of the AMS principal susceptibilities, but also an increase of the mean magnetic susceptibility (Km). Studied collections of loess/paleosol samples from different sections in Belgium, Bulgaria, China, Siberia and Tadjikistan and diorites, granites and gneisses from Antarctica show systematic Km-increase, between 2 and 27% as compared to the initial values, after AF-demagnetization up to 100 or 200 mT maximum amplitude. The relationships between magnetic susceptibility increase and magnetic hysteresis parameters and their ratios, indicate that the Km-increase is due to changes in magnetic domain configuration of the initial natural remanent magnetization (NRM) state of the remanence carriers during AF-treatment. The obtained linear relationship between K-increase and the degree of anisotropy P′ for strongly anisotropic gneiss samples suggests that magnetostatic interactions also play a role in the observed AF-effect on Km.