The change from paramagnetic resonance to ferromagnetic resonance for iron nanoparticles made by the sol–gel method Original Research Article

Sol–gel glass embedded with iron nanoparticles provides fascinating features inheriting paramagnetic, ferromagnetic, and superparamagnetic resonance properties under various compositional weight ratios and annealing conditions. Two spectra arising from paramagnetic Fe3+ ions and ferrimagnetic Fe2O3 particles both centered at ge=2.0 compete with intensities as the annealing temperature TA increases. Meanwhile, the resonance line width of Fe2O3 particles sharply decreases due to the strong exchange narrowing. The asymmetric line shape and the rather broad line width can be elucidated by the ferromagnetic resonance of the single domain Fe2O3 nanoparticles.