A Review of the Problem of Fine-Particle Interactions with Special Reference to Magnetic Recording

The problem of interactions between the fine iron oxide particles used in the coatings of magnetic recording tapes is reviewed. Particular attention is paid to the factors influencing the initial susceptibility of the anhysteretic remanence curve which is related to the sensitivity of the tape under high-frequency biasing conditions. As a satisfactory discussion of particle interactions and the anhysteretic process is not possible, it is necessary to rely on a number of theoretical models which are considered critically. For pairs of particles interacting positively or negatively a complete discussion is, however, possible, and this introduces the concept of anhysteresis as a growth process. This concept is then extended as far as possible to assemblies, where it is seen to be necessary to modify the usual Preisach model in a number of essential ways. The characteristic properties of several different recording tapes, namely the reduced saturation remanance and the initial anhysteretic susceptibility, are tabulated and discussed. Results for some other hard magnetic materials are also considered.