Microwave and magneto-optic properties of epsilon-Fe2O3 nanoparticles arising in borate glasses doped with Fe and Gd

The ε-Fe₂O₃ nanoparticles in borate glasses co-doped with low concentrations of Fe₂O₃ and Gd₂O₃ were investigated with two experimental techniques – visible magnetic circular dichroism (MCD) and electron spin resonance (ESR). The most prominent features of the MCD spectra are: non-linear dependence of the spectral maxima intensities on the Gd concentration and strong increase with the temperature decrease. The ESR spectra of these glasses exhibit two features with g = 4.3 due to the diluted Fe³⁺ ions and 2.0 associated both with Fe³⁺ ions and with nanoparticles. The integrated spectra intensities do not follow the T^-1 Curie law suggesting a considerable contribution from the magnetically ordered nanoparticles to ESR. Analysis of the MCD and ESR concentration dependences allow suggestion on the Gd ions incorporation into nanoparticles.