Direct Observation of Ferromagnetic State in Gold Nanorods Probed using Electron Spin Resonance Spectroscopy

TL;DR

This study provides direct ESR evidence of ferromagnetism in gold nanorods, revealing size-dependent magnetic properties and the role of spin-orbit interaction, which advances understanding of nanoscale magnetism.

Contribution

It is the first to directly observe ferromagnetic states in gold nanorods using ESR spectroscopy, highlighting size effects and spin-orbit coupling as key factors.

Findings

Ferromagnetic features depend on nanorod size.

A ferromagnetic transition occurs in the smallest nanorods.

Strong spin-orbit interaction contributes to ferromagnetism.

Abstract

X-band electron spin resonance (ESR) spectroscopy has been performed for gold nanorods (AuNRs) of four different sizes covered with a diamagnetic stabilizing component, cetyltrimethylammmonium bromide. The ESR spectra show ferromagnetic features such as hysteresis and resonance field shift, depending on the size of the AuNRs. In addition, the ferromagnetic transition is indicated by an abrupt change in the spectra of the two smallest AuNRs studied. A large g-value in the paramagnetic region suggests that the ferromagnetism in the AuNRs originates from strong spin-orbit interaction.