Observation of sphere resonance peak in ferromagnetic GaN:Mn

We report temperature-dependent optical spectra of ferromagnetic Mn-doped GaN in a wide photon energy region of 5 meV–4 eV. Below the GaN gap, an absorption peak around 1.25 eV whose intensity increases at lower temperatures was observed. A composite medium theory, called the Maxwell–Garnett theory, shows that the absorption peak can be assigned to a sphere resonance from metallic particles embedded in a Mn-doped GaN matrix. We also report that the far-infrared absorption of Mn-doped GaN sample was very small. This result suggests that itinerant carrier-mediated ferromagnetism does not fully explain the observed magnetic properties.