Magnetism in gold nanoparticles

TLDR

Gold nanoparticles are intensively studied for their unique properties across catalysis, optics, electronics, sensing, and theranostics, and a decade‑old magnetometry study revealed unexpected magnetic behavior that subsequent experiments confirmed but whose variability remains unexplained. This review compiles the experimental evidence concerning magnetic gold nanoparticles. It surveys and critiques the diverse theoretical models proposed to explain this anomalous magnetism. Despite extensive research, a definitive explanation is still lacking, suggesting that the range of hypotheses should be broadened.

Abstract

Gold nanoparticles currently elicit an intense and very broad research activity because of their peculiar properties. Be it in catalysis, optics, electronics, sensing or theranostics, new applications are found daily for these materials. Approximately a decade ago a report was published with magnetometry data showing that gold nanoparticles, most surprisingly, could also be magnetic, with features that the usual rules of magnetism were unable to explain. Many ensuing experimental papers confirmed this observation, although the reported magnetic behaviours showed a great variability, for unclear reasons. In this review, most of the experimental facts pertaining to "magnetic gold" are summarized. The various theories put forth for explaining this unexpected magnetism are presented and discussed. We show that despite much effort, a satisfying explanation is still lacking and that the field of hypotheses should perhaps be widened.