Detection of multi-axial magnetite by remanence effect on anisotropy of magnetic susceptibility

A method is here proposed to detect the presence of magnetic particles with multi-axial anisotropy, based on the effect of remanence on the anisotropy of magnetic susceptibility. The theory for an ensemble of single-domain particles with uniformly distributed orientation is shown and applied to a lava sample from Stromboli and to mid-oceanic ridge basalts. Results are coherent with the magnetic properties of the test samples and have successfully identified a small fraction of magnetic susceptibility carried by multi-axial grains where this was expected. Theory and experiments have shown that the remanence may have a large effect on the anisotropy of magnetic susceptibility which, however, can be effectively removed by alternating field demagnetization. It is also suggested that alternating field demagnetization should be routinely applied in rock-fabric studies of highly magnetized rocks.