ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Ni-Pd composite fine particle is an ideal system to study surface and interface magnetism because of its large surface area compared with the total volume. In this work, magnetic properties of Ni-Pd composite fine particles were studied in terms of the magnetic proximity effect and the effect of hydrogenation. The composite particle consists of Ni core and Pd shell. Five different particles with different Pd shell thicknesses, 50, 100, 150, 200, and 350 A(ring), were prepared. The average diameter of the Ni core is about 0.7 μm. The Curie temperatures of all the samples are lying around 630 K and are nearly equal to that of a bulk Ni. Unlike pure Ni, the samples exhibit a relatively large coercive force of a few hundred Oersted in the temperature range from 4.2 to 750 K. The magnetization of the Ni core is found to be somewhat lower than that of pure Ni. An enhanced interface anisotropy due to the Pd coating (∼−1.5×105 J/m3) seems to impede saturation. Before hydrogenation, there appears quite a large thermal hysteresis. On heating, the isofield magnetization exhibits ferromagnetic behavior with a rise of magnetic moment below 30 K, suggesting that there is induced magnetization in the Pd shell. The change in magnetization follows the Curie–Weiss law, which gives a Curie temperature of 22 K. However, the steep rise of magnetization is not observed in the cooling process. After hydrogenation, this ferromagnetic behavior completely vanishes. There is also observed no lattice expansion, but this isovolumetric constraint seems to have little change on the saturation hydrogen loading.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.355555
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