Temperature dependence of the coercivity of Fe films sputtered on nanochannel alumina

The morphology, magnetic microstructure, and temperature dependence of the magnetic coercivity of Fe films sputter deposited on commercial nanoporous substrates has been examined. Images obtained using Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) showed that the films grow in the form of a contiguous ferromagnetic network of small interconnected grains on the walls that separate the nanopores, Magnetic Force Microscopy (MFM) showed a very complex domain structured with magnetic clusters much larger than the grain size, This complexity in the magnetic structure is not unexpected if the network-like shape of the films is considered. The coercivity of all films increases as the temperature is decreased, the largest variation occurring for a film 5 mn thick. Maximum coercivities H-c, similar to 1800 Oe at 30 K were obtained in as-deposited 5 nm films. The temperature variation of H-c, for the thinner films was found to be qualitatively similar to that found in Fe particles covered with an oxide shell.