Magnetic properties of dispersed magnetite powders

Abstract

Measurements have been made of coercive force, susceptibility, isothermal remanence, thermoremanence and thermal and alternating field demagnetization of annealed magnetite powders in nine size ranges from 1·5 μ to 120 μ. The samples were dispersed in plaster to occupy a few per cent by volume of the specimens and thus to simulate the magnetic properties of rocks. The results are compared with the theories of rock magnetism. Susceptibility agrees precisely with theory and saturation remanence has the same dependence on coercive force as the theory. The observed values of thermoremanence are smaller than expected but show a size dependence consistent with the predicted appearance of pseudo-single domain effects at small grain size.