Permanent Magnetism in Dithiol-Capped Silver Nanoparticles

Silver nanoparticles, capped with oleic acid, with mean diameters varying between 2.8 and 5.7 nm, have been synthesized by the polyol method and 1,6-hexane dithiol was subsequently substituted for the oleic acid. Whereas oleic acid-capped silver nanoparticles, like bulk silver, show a diamagnetic behavior, dithiol-capped silver nanoparticles exhibit a permanent magnetism, with a finite coercivity, up to room temperature. The permanent magnetism is associated with blocked, highly anisotropic localized magnetic moments at the particle surface, due to the spins of 4d localized holes generated through Ag-S bonds. The strong anisotropy is a result of the combination of spin-orbit coupling and the breaking of lattice symmetry of surface particle Ag atoms involved in both Ag-Ag and Ag-S bonds.