Correlation between Rayleigh loops and frequency‐dependent and quadrature susceptibility: Application to magnetic granulometry of rocks

Abstract

We report the results of measurements of frequency‐dependent and quadrature low‐field magnetic susceptibility of basalt specimens showing different types of low‐field hysteresis (Rayleigh) loop. A correlation among the three techniques is demonstrated, with specimens showing broad and constricted loops exhibiting relatively high‐frequency dependence of susceptibility and a high ratio of quadrature to in‐phase susceptibility. This result has implications for magnetic granulometry studies of rocks. Broad and constricted Rayleigh loops indicate the significant contribution of hyperfine grains to the magnetic properties of specimens; however, with the current instrumentation, low‐field hysteresis loop measurements are restricted to relatively strongly magnetic specimens. For weakly magnetic rocks and sediments, measurement of the frequency dependence of susceptibility or the quadrature susceptibility permits rapid identification of specimens in which hyperfine grains significantly influence the magnetic properties.