Magnetism in dodecanethiol-capped gold nanoparticles: Role of size and capping agent

Abstract

In gold nanoparticles (Au NPs) capped with dodecanethiol (DT), the authors report the observation of superparamagnetic blocking temperature TB ≃50 K in D≃5 nm NPs but only diamagnetism in 12 nm NPs. For T< TB =50 K, the strong temperature dependence of coercivity Hc, saturation magnetization Ms, and exchange bias He (in the field-cooled sample) confirm the blocked state resembling ferromagnetism with Hc ≃250 Oe, He ≃-40 Oe, and Ms ≃ 10-2 emug at 5 K. The observed electron magnetic resonance line shows expected shift, broadening, and reduced intensity below TB. A magnetic moment μ≃0.006 μB per Au atom attached to DT is determined using a model which yields Ms varying as 1D, with its source being holes in the 5d band of Au produced by charge transfer from Au to S atoms in DT. © 2007 American Institute of Physics.