The piezomagnetic effect in rocks: a comparison of measurements in high and low fields |
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| Authors: | Jin-qi Hao LG Parry GJ Tuck FD Stacey |
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| Institution: | 1. Physics Department, University of Queensland, Brisbane, Qld. 4067 Australia;2. School of Physics, University of New South Wales, Kensington, N.S.W. 2033 Australia |
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| Abstract: | There are some puzzling features of the stress-dependence of magnetic susceptibility in rocks, although the behaviour in high fields appears to be well understood. As a test for the factors that cause low-field behaviour to differ from current theories we have made both high- and low-field torquemeter measurements of the stress-induced magnetic anisotropies of a number of rocks. Ratios of low- and high-field torques differing from expectation by factors up to 4 or so have been found in some rocks, although others conform well to expectation. A comprehensive study of magnetic and microscopic properties was undertaken to seek the cause(s) of the discrepancies. Stress sensitivity of susceptibility becomes particularly high in titanomagnetite with composition parameter x ≈ 0.6, at which the intrinsic anisotropy vanishes, and some other high values appear to be related to the presence of sulphide. It is concluded that current theory is satisfactory if but only if the magnetic minerals in a rock are simple titanomagnetites with x ? 0.4. |
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