Unusual ferromagnetic behaviour of embedded non-functionalized Au nanoparticles in Bi/Au bilayer films

Abstract

There is a growing consensus through various experimental and theoretical studies that gold can exhibit magnetic properties at low dimensions in contrast to its well-known diamagnetic nature when in bulk form. Although theoretical simulation studies show that bare gold nanoclusters can be intrinsically magnetic, experimental reports to prove this theory are scarcely available since most of the studies are based on functionalized gold nanoparticles. In this article, we report unusual ferromagnetic behaviour that is observed in embedded non-functionalized Au nanoparticles using superconducting quantum interference device (SQUID) magnetometry. These nanoparticles are obtained after irradiating thermally deposited Au/Bi double bilayer films using 1.5 MeV Au ions at different fluences from 5 × 10¹⁴ to 1 × 10¹⁶ ions per cm². A detailed study of cross-sectional high resolution transmission electron microscopy (X-HRTEM) results for the irradiated sample confirms the presence of embedded Au nanoparticles with an average size of 2.61 nm. The unusual ferromagnetic behaviour is attributed to these embedded Au nanoparticles that were formed after ion irradiation.