ANISOTROPY-FIELD DISPERSION IN RECORDING MEDIA

The magnetic recording media in use today range widely from dispersions of acicular particles of gamma-Fe2O3, CrO2, Co-gamma, and metal particles (all with predominant shape anisotropy) to dispersions of platelet-shaped Ba-ferrite particles and thin film metallic media (with predominant crystal anisotropy). Well-oriented particulate media with shape anisotropy particles have much wider remanence switching field distribution (SFDr) than do oriented Ba-ferrite media or texturized thin film media. Very small SFDr values and correspondingly high values of coercive squareness (S) in the latter type of media are at times, but not always, associated with high media noise (transition noise observed in the presence of signal) resulting from exchange coupling of the crystallites in thin film media or stacking of the platelets in Ba-ferrite media. In cases where the SFDr values are very low, but the noise is not high, it has been suggested that the underlying reasons may be due to narrow distributions of anisotropy fields. In this study, we measured the Hk distribution in many different commercial samples of particulate and thin film media. In all cases, we found relatively large Hk distributions, which do not seem to correlate with the SFDr (or S) values or with the media noise. This leads to the conclusion that switching field distributions in oriented media do not derive from or relate to the anisotropy field distributions in these media. © 1990 IEEE