Magnetism of iron nanoparticles in rare Earth matrices.

This thesis details three main studies. The first is an investigation of the effect of coating Fe nanoparticles in a gas to isolate the magnetic moments. An isolation or enhancement of the already increased magnetic moment of a Fe nanoparticle would have the potential for exploitation in high-moment materials. The two other investigations are of the behaviour of Fe nanoparticles in the rare earth matrices Ho and Dy. Transition metals and rare earth metals normally couple antiferromagnetically at their interface, however the intention of this work was to determine if this also happens when the Fe is incorporated as pre-formed clusters. The motivation for this is that if the interactions between the rare earth and the transition metal is switched to be ferromagnetic then the Curie temperature of the rare earth could be increased without a large decrease in its saturation magnetisation. Fe nanoparticles consisting of -200 atoms and -2nm in diameter were manufactured using a gas aggregation source then coated with H2(g). VSM, XMCD and TEM measurements were taken of these samples and the magnetic moment per atom of Fe was found to drop significantly compared to that of isolated clusters in Ag matrices. A comparative study using N2(g) was conducted yielding similar results. This is attributed to the gas permeating the whole cluster rather than forming a shell. Addition of atomic Fe to a rare earth matrix decreases the total magnetisation due to antiferromagnetic coupling. Fe nanoparticles deposited into rare earth matrices heavily quench the rare earth moment. Samples of 2-35% Fe by volume contain Fe nanoparticles large enough to disrupt the rare earth spin wave. The Fe nanoparticles couple ferrimagnetically to the rare earth producing the low overall magnetic moment. Several magnetic phase transitions were observed in all Fe/rare earth alloys. Structural measurements using EXAFS indicate that the Fe clusters may have changed to an expanded lattice within the Dy matrix.