Magnetic and microstructural analysis of palladium nanoparticles with different capping systems

Abstract

Palladium nanoparticles capped with different protective systems in a size range between 1.2 and 2.4 nm have been obtained by varying the preparation chemical method. Magnetization curves for all the samples show hysteresis loops, evidencing a ferromagnetic or a permanent magnetism in the nanoparticles. The microstructure of the nanoparticles has been analyzed by x-ray absorption and transmission electron microscopy. The nature of the magnetic behavior found for all these Pd nanoparticles (NPs) is different depending on their sizes and structural features and is explained on the basis of two different suggested mechanisms. The particles protected by means of a surfactant (tetralkylammonium salts), present a ferromagnetic order related to the factors increasing the density of states just below the Fermi level. Whereas, when the nanoparticles are stabilized by covalent bonds with protective species (thiol derivatized alkane chains or surface oxidized Pd NPs), the increase of the $4d$ density of holes, localized by the bonded atoms (S or O), is giving rise to the observed ferromagneticlike behavior.