THERMAL FLUCTUATION ANALYSIS - NEW TECHNIQUE IN ROCK MAGNETISM

Thermal fluctuation analysis is a new method of determining ″magnetic grain size″ , v and microscopic coercive force H//K in particles too small for direct domain observations. When it is used with single-domain particles, thermal fluctuation analysis is a method of magnetic granulometry, since v is the physical grain volume and H//K is usually closely related to grain shape. Thermal fluctuation analysis is the only simple means of calculating average v and H//K separately. The method is tested by applying it to single-domain materials of known grain size. Fluctuation analysis is then used to infer the possible domain structure of 500- to 2200-A magnetite particles and to point up a deficiency in an earlier procedure for detecting ordering of lattice defects impeding domain wall motion. Potential broader applications include determining mean grain sizes of single, and under favorable conditions, double populations of magnetic carriers in rocks, defining average elongation for single-domain particles in rocks and synthetic dispersions (e. g. , magnetic recording tapes), and deducing the mechanism of anisotropy or of opposition to wall motion.