CoW alloy clusters with extended solubility of W in hcp Co were produced by inert-gas condensation. The structural state of the as-deposited CoW clusters was found to be critically dependent on processing parameters such as the cooling scheme and sputtering power. For the water-cooled clusters, the mean size and percent crystalline were strongly dependent on sputtering power, while the percent crystalline of the liquid nitrogen-cooled clusters was not as affected by the sputtering power. At low sputtering powers, the water-cooled clusters were predominantly amorphous, but became increasingly more crystalline as the sputtering power increased. The predominant crystalline phase was hcp Co(W), but high-resolution transmission electron microscopy revealed that very small and very large clusters contained fcc and Co3W structures, respectively. For liquid nitrogen cooling the clusters were predominantly amorphous regardless of sputtering power, although at the highest sputtering power a small percentage of the clusters were crystalline. The magnetic properties were dependent on cooling schemes, sputtering power, and temperature, with the highest coercivity of 893 Oe obtained at 10 K for water-cooled clusters sputtered at 150 W. The magnetocrystalline anisotropy of the water-cooled sample increased with increasing sputtering power, with the highest anisotropy of 3.9 × 10 6 ergs/cm 3 recorded for clusters sputtered at 150 W. For liquid nitrogen-cooled samples, the anisotropy was approximately constant for all sputtering powers.
In this article, inert-gas condensation was used to synthesize Co-W clusters. The formation, structure, and magnetic properties of the clusters were investigated. Sub-10-nm clusters were obtained, and the structures and average sizes were strongly dependent on sputtering power. At low sputtering powers, the clusters were predominantly amorphous, while, at high sputtering power, the clusters were crystalline. X ray diffraction and transmission electron microscopy revealed clusters with hcp structure at high sputtering power. The magnetic properties were dependent on the sputtering power and temperature, with the highest coercivity of 810 Oe at 10 K for high sputtering power.
Equiatomic FeAu nanoclusters were produced by inert-gas condensation and embedded in a W matrix. Transmission electron microscopy investigation shows that three kinds of clusters are present: mono-crystalline, polycrystalline, and partially crystalline clusters. It demonstrates that during their formation, the structure of nanoclusters evolves from an amorphous to a crystalline structure. Crystallisation starts at the surface of nanoclusters and currently leads to the formation of poly-crystalline nanoclusters in the end. Most of the investigated objects consist in a duplex amorphous core-crystalline shell structure. Their magnetic properties were investigated by magnetization measurements as a function of magnetic field (hysteresis loops) or temperature (ZFC/FC curves). They show evidence at low temperatures of ferromagnetic and antiferromagnetic states, and ordering as well as superparamagnetism or spin-glass behaviour. Measurements performed after cooling the samples under various applied fields reveal the occurrence of exchange-spring phenomenon, related to the presence of the W matrix, through RKKY coupling between ferromagnetic and antiferromagnetic nanoclusters. V C 2013 AIP Publishing LLC.
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