Magnetic susceptibility under hydrostatic pressure of synthetic magnetite samples

Artificial specimens containing magnetite of various grain sizes and in different concentrations have been used to study the behaviour of 15 directional susceptibilities under hydrostatic pressure of up to 20 MPa (0.2 kbar). With increasing pressure a moderate but systematic decrease of all directional susceptibilities has been measured. These changes are reversible with respect to the pressure applied. The maximum decrease in susceptibility has not exceeded 3% of the original value, and the differences in pressure sensitivity of magnetite with varying grain size are minimal. In the case of relatively homogeneous transfer of stress across an isotropic matrix, the cause of the susceptibility decrease is probably the decreased mobility of the domain walls under hydrostatic pressure.