FMR linewidth and magnetic structures in CoFe-Al2O3 granular thin films

For thin films with CoFe magnetic granules, embedded into insulating Al3O3 matrix by different preparation techniques, a comparative study of ferromagnetic resonance (FMR) linewidth has been done in function of temperature and granule content. The films obtained by oblique co-deposition present a 3D granular structure and an in-plane magnetic anisotropy, attributed to granule elongation at their high enough content. In the discontinuous multilayered systems prepared by ion-beam deposition, an almost isotropic 2D structure dominates. This structural distinction leads to the difference in temperature behavior of FMR linewidth, the latter being attributed mainly to static fluctuations of demagnetizing field. These fluctuations attend maximum in function of CoFe content near the magnetic percolation point. Also they are enhanced at decreasing temperature, with the greatest variation observed in the layered granular films below magnetic percolation, probably due to getting below ac blocking temperature.