Magnetic behaviour and percolation in mechanically alloyed Fe-SiO2 granular solids

In this paper we report a study of the coercivity of Fe-SiO2 granular solid s, with Fe volume concentrations between 0.2 and 0.6, and mean grain sizes varying from 15 to 18 nm. These samples present very high switching fields of the order of 1 kOe, being higher for the magnetization processes than fo r the demagnetization ones. The analysis of the switching held distribution s and the calculation of the activation volumes have proved that the revers al mechanism is the same for all samples, either above or below the percola tion threshold (x = 0.5), and involves the full volume of individual partic les, aided by dipolar fields that are of a few hundred Oe, in the case of t he demagnetization processes. (C) 2000 Elsevier Science B.V. All rights res erved.