Particle Interaction in Magnetic Recording Tapes

The magnetic coating of recording tape is assumed to be composed of an assemblage of small, single-domain particles. Each particle is assumed to have a symmetrical, square hysteresis loop when the reversible component of magnetization is neglected and when the particle is not influenced by the fields of neighboring particles. When influenced by the fields of its neighbors, the particle may exhibit an asymmetrical loop when the loop is plotted relative to an external applied field. In this case the positive and negative switching fields for the particle are not equal, and their difference gives an indication of the particle interaction. While it is not possible to measure the switching fields of a single particle on the recording tape, the distribution of switching fields in the assemblage of particles and the associated magnetic moment can be measured. The two switching fields and the magnetic moment define a 3-dimensional distribution function which describes the magnetic properties of the tape, and in terms of which both dc and anhysteretic magnetization processes may be described. The distribution functions have been measured for two recording tapes. While the functions for the two tapes are markedly different in detail, both show that particle interaction is very appreciable in recording tapes and that it is a significant factor in determining the bulk magnetic properties and the recording performance of tapes.