Effect of gadolinium on magnetic circular dichroism and electron magnetic resonance of epsilon-Fe2O3 nanoparticles formed in borate glasses

A remarkable characteristic of borate glasses is the ability of forming magnetic nanoparticles at low doping with transition element oxides. We have studied structure and magnetic properties of iron oxide nanoparticles formed in borate glasses, in particular, concentration and temperature dependences of magnetic circular dichroism (MCD) and electron magnetic resonance (EMR) spectra. A series of glasses of molar composition 22.5K₂O-22.5Al₂O₃–55B₂O₃ doped with 1.5 mass % of Fe₂O₃ and different contents of Gd₂O₃ from 0.1 to 1.0 mass % was prepared using a conventional melt quenching technique and subjected to an additional thermal treatment. The whole set of results allows to identify the predominant magnetic phase in these glasses as ε-Fe₂O₃ nanoparticles, with a considerable part of iron ions substituted by gadolinium. Analysis and computer simulations of the EMR spectra allow separating the contribution of electron paramagnetic resonance of diluted iron ions and together with the temperature dependences of magnetization demonstrate a superparamagnetic character of the nanoparticle magnetism.