Magnetism of Fe and Co nanostructured materials

The main purpose of this work was to produce a material with a saturation magnetisation greater than 2.45 T, the highest known value, which occurs in the alloy Fe65Co35.;In situ XMCD measurements carried out on size selected Fe nanoclusters deposited onto HOPG substrates revealed an enhancement of the orbital and spin moments above the bulk values for these systems. The measurements also show that there is a further increase in the moments when the Fe clusters are coated with Co. These experiments took place on beamline ID12B at the ESRF in Grenoble.;Following on from the XMCD results, samples were made consisting of Fe nanoparticles embedded in a Co matrix, and also, of Co nanoparticles embedded in a Fe matrix. The average magnetic moment per atom in these novel nanostructured materials was obtained from magnetisation curves as measured by a VSM. The results are compared to the Slater-Pauling curve for conventional Fe-Co alloys, and show that the magnetic moment per atom in samples containing up to about 20 at.% Fe nanoclusters embedded in a Co matrix (80 at.%) is larger than in the corresponding conventional Fe-Co alloy. There is a sharp drop in the moment above this concentration. Similarly, for samples with up to 20 at.% Co clusters embedded in a Fe matrix the moment per atom is above the Slater-Pauling curve. However, in the case of the latter, the enhancement in the magnetisation is significantly above the peak of the Slater-Pauling curve.;In order to determine the atomic structure of the embedded clusters, EXAFS measurements were carried out on both types of sample described in the previous paragraph. These experiments were performed on beamline 7.1 at the SRS in Daresbury. Fe nanoclusters embedded in Co were found to have the bcc structure, as in bulk Fe. However, simulations of the EXAFS data for Co clusters embedded in Fe show that the Co clusters adopt a bcc structure, as compared to hcp in bulk Co.