The isothermal remanent magnetisation of fine magnetic particles

The effect of a finite maximum applied field on the remanence of a fine-particle system with uniaxial anisotropy and easy axes aligned parallel to the applied field is investigated. Theoretical calculations are presented for iron, cobalt and Fe 3 O 4 particles, and it is shown that large values of remanence are obtained for large values of the product KV (K is the anisotropy constant and V the particle volume). For practical purposes a technique is outlined whereby optimum values of K and V may be chosen in order to maximise the remanence of the system. Measurements are presented of the remanence of a system of fine cobalt particles as a function of the maximum applied field and a comparison made with the theoretical predictions.