Low-Temperature Magnetism in Nanoscale Gold Revealed through Variable-Temperature Magnetic Circular Dichroism Spectroscopy.

The low-temperature (0.35-4.2 K) steady-state electronic absorption of the monolayer-protected cluster (MPC) Au102( pMBA)44 was studied using magnetic circular dichroism (MCD) spectroscopy to investigate previously reported low-temperature (<50 K) magnetism in d10 nanogold systems. Variable-temperature variable-field analysis of resolvable MCD extinction components revealed two distinct magnetic anisotropic behaviors. A low-energy, diamagnetic component was correlated to excitation from states localized to the passivating ligands. A high-energy, paramagnetic component was attributed to excitation from the d-band of the Au core. The temperature dependence of the magnetic anisotropy for each component is discussed in terms of previously reported structural parameters of the atomically precise Au102( pMBA)44 MPC. It is concluded that temperature-sensitive structure-dependent Au d-d orbital interactions result in the promotion of 5d-band electrons to the 6sp-band via orbital rehybridization, inducing a 15× increase in the Landé g-factor over the temperature range spanning from 0.35 to 4.2 K.