Ferromagnetic films deposited on nanochannel alumina

Interest in artificially grown nanostructures has grown enormously in the last few years because of the potential applications in the magnetic recording industry. In this work we present ferromagnetic resonance investigations performed on Fe films sputter-deposited on nanochannel alumina (NCA). These films form a network-like nanostructure on top of the walls that separate the pores. The geometry is fixed by the channel size, the porosity of the substrate and the film thickness. From the experimental results in NCA of 20 nm pore diameter we have found that thinner films (10 nm or less) are discontinuous and formed by isolated, partially oriented anisotropic particles. An average aspect ratio of ∼1.5 was estimated for the particles forming the film. As the film thickness increases the effective anisotropy (mostly shape anisotropy) tends to reach a saturation value for films thicker than 75 nm. For NCA substrates of larger pore diameter (100 nm and 200 nm pore size) the effective anisotropy is greatly reduced and even changes orientation for the thinner films. This behavior is interpreted as comming from a faster filling of the pores with the sputtered material in the substrates with smaller pore size. Received: 30 March 2000