Magnetic resonance in iron oxide nanoparticles: quantum features and effect of size

TL;DR

This study investigates electron magnetic resonance in iron oxide nanoparticles of different sizes to understand the quantum-to-classical transition in spin systems, revealing size-dependent spectral features and transition behaviors.

Contribution

It provides new insights into how quantum features in EMR evolve with nanoparticle size, bridging understanding between quantum and classical magnetic behaviors.

Findings

Quantum EMR features diminish with increasing particle size.

Temperature affects the spectral components, indicating quantum-classical transition.

Both magnetite and maghemite nanoparticles show similar EMR behaviors.

Abstract

In order to better understand the transition from quantum to classical behavior in spin system, electron magnetic resonance (EMR) is studied in suspensions of superparamagnetic magnetite nanoparticles with an average diameter of ~ 9 nm and analyzed in comparison with the results obtained in the maghemite particles of smaller size (~ 5 nm). It is shown that both types of particles demonstrate common EMR behavior, including special features such as the temperature-dependent narrow spectral component and multiple-quantum transitions. These features are common for small quantum systems and not expected in classical case. The relative intensity of these signals rapidly decreases with cooling or increase of particle size, marking gradual transition to the classical FMR behavior.