Investigation of the precipitation kinetics and changes of magnetic anisotropy of iron particles in ion-irradiated silica gel films by means of electron-spin resonance

This paper reports the effect of the density of ion-induced electronic excitations on the nucleation of Fe particles in a silicon-based gel and on the magnetic ordering in SiO2:Fe composites with a volume fraction of metal of a few percent derived from the same gel. The nucleation occurs for a critical value of the energy density deposited by ions in electronic excitation. The dependence of the nucleation yield on the ion fluence φ is determined by the product of the electronic energy loss Se and the number n of ion impacts on a same area a which are necessary for reaching locally this critical energy density. Irradiation-induced changes in the magnetic anisotropy of composite films, previously formed by heat treatment of the same gel, depend more drastically on the order of magnitude of Se. When the latter is high enough for damaging the matrix, a tilt of the easy magnetization axis is observed