Effect of gadolinium ions on the structure and magnetic properties of zinc-borate glasses and glass ceramics

X-ray diffraction (XRD), electron paramagnetic resonance (EPR), and magnetic susceptibility measurements have been employed to investigate the samples from the (Gd2O3) x ·(B2O3)(60−x)·(ZnO)40 (0 ≤ x ≤ 20 mol%) system. The XRD pattern for the prepared samples shows that the vitreous phase is present only for x ≤ 15 mol%. For the samples containing 20 mol% Gd2O3 the presence of a unique crystalline phase, GdBO3, embedded in a vitreous matrix was evidenced. In this case the XRD patterns show the presence of nanometer sized crystals (64 nm) in a glassy matrix. The EPR spectra of the studied samples exhibit three important features with effective g-values of ≈6, 2.8, 2.0 and a weaker feature at g ≈ 4.8. For low Gd2O3 contents (x < 3 mol%), the EPR spectra have the typical ‘‘U’’-type shape. For higher contents of Gd2O3 (x ≥ 3 mol%), the spectral features are broadened and finally are dominated by a single broad absorption line located at g ≈ 2.0. This broad EPR line is associated to the Gd3+ ions present predominantly as clustered species. Magnetic susceptibility data show that for x > 1 mol% the Gd3+ ions are present not only as isolated species but also as species coupled through antiferromagnetic exchange interactions.