Magnetic interactions in particulate and thin-film recording media

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Abstract
Magnetic interactions between particles or crystallites in recording media can have an important effect on their switching behavior and on their recording performance. If the types of interactions that tend to stabilize the saturated state are defined as positive and those that tend to destabilize it as negative, it can be argued that positive interactions would reduce demagnetization losses and lead to improved recording performance. Furthermore, positive interactions would be expected to give rise to cooperative switching of groups of particles or crystallites that, on the one hand, would tend to reduce the switching field distribution and, on the other hand, would tend to increase noise. Remanence curves, being strongly influenced by interparticle interactions, provide a sensitive way to investigate the magnitude and sign of such interactions. In this paper, the interactions of different particulate and thin-film media have been studied by comparing their demagnetization remanence curves with their isothermal remanence curves. Recording media employing oriented acicular particulate assemblies exhibit negative interactions. Nonoriented particulate media with either acicular or platelet-type particles exhibit very small and slightly negative interactions. Thin-film media and oriented Ba-ferrite media with platelet-type particles usually exhibit strong positive interactions. These large differences in interaction fields are discussed on the basis of the type of coupling (magnetostatic and/or exchange), the particle morphologies, and the anisotropy fields in these media. The polarity, magnitude, and shape of the interaction curves seem to be qualitatively correlated with the recording media noise.