Gyroremanent magnetizations in dilute anisotropic dispersions of gamma ferric oxide particles from magnetic recording tape

The dependence of gyroremanent magnetization (GRM) on anisotropy for samples containing dilute dispersions of partly aligned γ-Fe2O3particles has been determined by applying an alternating field (AF) of typically 60-mT peak at various angles (θxy) to the axis of maximum alignment (x) in the x-y plane and slowly reducing it to zero. The GRM produced is along the z axis and exhibits a dependence with a maximum which can be related to the anisotropy in the x-y plane and to the rotational remanent magnetization (RRM) acquired parallel to the rotation vector when the sample is rotated about its z axis near twice the AF frequency. The AF was normal to the rotation vector and was slowly reduced to zero with all other external fields removed. The measurement of an anhysteretic remanent magnetization (ARM) produced by applying a weak steady field along the rotation vector in the presence of the strong AF allows the determination of an effective field (Bg) which can be considered to produce RRM. This was found to be independent of anisotropy and of sample (and, therefore, particle) orientation in the rotation system. It is very probable that gyromagnetic remanences will be produced during the magnetic recording process because the experimental conditions above are similar to those experienced by the recording medium.