Gyromagnetic remanence produced by rotation of magnetite and maghemite particles in a slowly reducing direct field

Abstract

Samples containing dispersed magnetite and maghemite particles have been rotated in the presence of a slowly reducing direct field (initially either 60 or 80 mT) applied normal to the rotation axis. This treatment produces a remanence (rotational remanent magnetization or RRM) which is parallel to the rotation vector and is of the same strength as that produced by high-speed rotation in a slowly reducing alternating field (AF). Comparison with the anhysteretic remanent magnetization (ARM) obtained by applying a known weak field (70 μT) along the rotation axis at the same time as the much stronger direct field reduces, enables an effective field B' g to be determined which can be considered to produce RRM. B' g is found experimentally to be identical to the corresponding field B g obtained when high-speed rotation in an AF is employed. These results are consistent with the hypothesis that the effective field (and hence RRM) is generated by a gyromagnetic effect associated with the rapid switching of the moments of single-domain particles.