Unveiling unsaturated modes from multi-frequency ferromagnetic resonance using maghemite nanoparticles

Abstract

This study reports on the use of ferromagnetic resonance (FMR), at various microwave frequencies (1.1 GHz, 3.5 GHz, 9.4 GHz, and 33.9 GHz), to investigate nanosized maghemite-based (γ-Fe₂O₃) samples in both powder (P) and aqueous-based magnetic fluid (MF) presentations. The structure of the as-synthesized sample was confirmed through x-ray diffraction (XRD), revealing the maghemite phase with average diameter of about 12 nm. Analyses of the room temperature (RT) FMR spectra suggest that the samples are in a non-saturated state for microwave frequencies below about 10 GHz (X-band). Comparisons between theoretical modelling (acceptable) parameters and those obtained through fittings of the experimental data revealed significant discrepancies, highlighting an increase in divergence as the measurement condition deviates from the magnetic saturation condition, taking place at microwave frequencies below about 10 GHz.