Investigation of the Magnetic Properties of Non-Thiolated Au Nano-Structures Grown by Laser Ablation

Abstract

Although it is known that gold (Au) is diamagnetic in bulk form, it has been reported that Au displays magnetic properties when reduced to the nano-scale. Researchers found magnetism in Au nanoparticles (NPs) in a size range from 2 to 10 nanometers. Moreover, the Au nanoparticles are usually coated by thiol-containing organic caps, which are believed to be responsible for the magnetism. However, others suggest that organic capping is not necessary to observe magnetism in Au NPs, and magnetism may be an intrinsic property for nano-structured gold. For this investigation, we used pulsed laser deposition to prepare nano-structured gold of different sizes and concentrations to investigate the magnetic properties. Our experiment results confirmed that for the samples in which Au is in the metallic state as nanoparticles with ~5 nm diameter, as well as inthe alloy form, bonded with indium, the samples show ferromagnetism when embedded in an Al2O3 matrix without any thiol-containing organic capping. Our results suggest that ferromagnetism is an intrinsic property of Au nano-structures, which means that it is not necessary to incorporate Au-S bonds with organic coatings in order to observe this phenomenon. We believe due to the significant broken symmetry at the surface of the nanoparticles, holes are generated in d bands of the surface Au atoms. These holes are most possibly responsible for ferromagnetism in Au nanoparticles. The realization of magnetism in Au coupled with the lack of clear understanding of its origin makes the investigation of magnetism of diamagnetic metals ripe for further inquiry.