Nanostructured Fe networks studied by ferromagnetic resonance

When a material is sputter-deposited on a nanoporous substrate a network-like film is formed on top of the walls that separate the nanochannels. We have carried out an extensive study of the magnetic properties of Fe films deposited on 20 nm pore size nanochannel alumina. Films covering the thickness range 5 nm to 100 nm were characterized using ferromagnetic resonance. From the experimental results it was inferred that thinner films are discontinuous (probably due to the surface roughness) and composed of isolated, partially oriented, anisotropic particles. The resonance field and linewidth have been used to estimate the effective anisotropy and hence an average particle aspect ratio of 1.5, which is very similar to what is actually observed by direct imaging. The effective anisotropy increases for thicker films and tends to saturate for films thicker than 75 nm.