Yttria-Coated FeCo Magnetic Nanoneedles

Yttria-coated FeCo nanoneedles with a Co content up to 30 mol % were obtained by thermal reduction of oxyhydroxide precursors. Incorporation of Co and Y elements, with the adequate sequential distribution, to the Fe-based oxyhydroxides was carried out by an oxidation-precipitation method followed by a template method. Special emphasis has been set to correlate the physicochemical characteristics with the magnetic properties of the obtained samples. In this way, Mossbauer and X-ray photoelectron spectroscopy have allowed us to determine that the FeCo metallic core of the particles consists of areas with Fe and Co atoms randomly distributed and also forming clusters. We also established that the improvement in coercivity in metallic particles coated with yttria instead alumina could be associated with the higher degree of thermal protection supplied by yttria. We found that the highest values of coercivity (1550 Oe) are obtained for the yttria-coated FeCo metallic samples with a Co content of 20 mol %. Finally, differences in coercivity between the samples containing different Co content have been associated with both the Co content and microstructure.