| Abstract
| - Ferromagnetism in carbon-coated platinum nanoparticles prepared by laser ablation is reported. Electron microscopy shows that nanoparticles exhibit a large concentration of twin boundaries which reduce the surface energy. The large spin−orbit coupling of Pt accounts for a huge magnetic anisotropy and therefore for a high blocking temperature, above 300 K.
- In this paper, we report on the preparation and magnetic properties of small Pt nanoparticles (2−5 nmsize). The control of the preparation conditions allow the physical properties of the nanoparticles to betuned, giving rise to properties different from those of bulk Pt. We show here the first experimentalobservation of ferromagnetic behavior for carbon-coated platinum nanoparticles with coercivity up toroom temperature (i.e., surprisingly there are no superparamagnetic effects despite the small size of thenanoparticles). Measurements of the surface plasmon resonance showed the presence of itinerant electrons.TEM studies confirmed that the nanoparticles exhibit a large concentration of twin boundaries whichreduce the surface energy. The lack of cubic symmetry at the twin boundaries could give rise to permanentmagnetic moments. The large spin−orbit coupling of platinum accounts for a huge magnetic anisotropyand therefore for the surprisingly high blocking temperature, above 300 K. The relationship of the magneticproperties with the particle structure is also discussed.
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