Magnetic properties of thiol-capped gold nanoparticles

We present the experimental results of magnetization measurements on thiol-capped gold nanoparticles (Au-SR NPs) synthesized in a two-phase liquid-liquid system. The size of particles ranged from 2.0 to 3.5 nm with an average size of 2.8 nm. The magnetic properties of Au-SR NPs were characterized by a mixture of ferromagnetic, paramagnetic and diamagnetic components. Magnetization curves showed the hysteresis behavior typical of a ferromagnet over the whole temperature (T) range investigated (2 K to 300 K) whereas M(H) did not saturate, not even at low T, implying the existence of a paramagnetic component. The negative slope of M(H) observed at high T demonstrated that a diamagnetic component was also considerable. From a theoretical fit, we obtained effective values of parameters such as the paramagnetic effective moment, μ_p = 5.7 μ_B, and the diamagnetic susceptibility, χd = -1.7 × 10^-7 emu/gOe. In addition, the T-dependence of the ferromagnetic component M_f (T) was extracted from the experimental M(T), and its characteristics are discussed in the light of the mean field model.