Magnetic properties of nanostructured thin films of transition metal obtained by low energy cluster beam deposition

Publisher Website
Google Scholar
Abstract
Clusters of iron, cobalt, and nickel are produced in a laser vaporization source. The size distributions of the incident clusters are checked by time‐of‐flight mass spectrometry before deposition at low energy. Studying the near threshold photoionization, Con and Nin clusters exhibit an icosahedral structure while for iron, no clear structure emerges. Neutral clusters were deposited on different substrates at room temperature with thicknesses up to 100 nm in view to determine their structure and magnetic properties. A limited coalescence of the clusters is observed from high‐resolution transmission electron microscopy. No icosahedron has been observed but cuboctahedron and interface twins between adjacent particles have been clearly identified in Ni films. Grazing incidence x‐ray diffraction experiments reveal a classical phase with grain size around 6 and 4 nm for Fe and Ni films, respectively but an anomalous fcc phase for Co films and a very low grain size of 2 nm. The density of films determined by x‐ray reflectivity was estimated to represent only 60%–65% of the bulk density. Magnetic behaviors studied by ferromagnetic resonance and SQUID magnetization measurements have been interpreted using the correlated spin glass model. Mössbauer spectra performed on Fe films at zero field revealed the presence of 20% of iron in the form of thin nonmagnetic oxide skin surrounding Fe grains which allow to find 2.2 μB per magnetic iron atom in agreement with macroscopic magnetic measurements. Nevertheless we found an anomalous reduced atomic moment for Ni film.