Electron Magnetic Resonance in Magnetic Nanoparticles: Dependence on the Particle Size and Applicability of the Modified Giant Spin Model

Abstract

Electron magnetic resonance is experimentally studied in dilute solid suspensions of iron oxide nanoparticles as the function of the particle size, and discussed in the frames of the modified giant spin approach. Gradual evolution of features specific for small nanoparticles including a narrow component at the main resonance field and a weak half-field line is observed with the increase in the particle size, manifesting the transition from quantum to fully classical behavior. The shape, width, position of the resonance spectra, and the specific features are described quantitatively with a single set of fitting parameters for nanoparticles of 5–20 nm size. Limitations of the quantum model at high spin values are discussed.