Publications

EPR measurements were conducted at different temperatures 100K ≤ T ≤ 295K for GdBa2Cu3O7-δ superconducting samples prepared by the conventional solid state reaction technique, added with x wt.% nanosized ferrite of CoFe2O4, prepared by chemical co precipitation method, with 0 ≤ x ≤ 0.40 wt.%. A broad isotropic symmetric EPR line with g factor g ≈ 2 is detected for the (CoFe2O4)xGdBa2Cu3O7-δ samples, corresponding to Gd3+ ions. The broadness is attributed to the superposition of signals resulting from the clustering of Gd3+ ions and the dipole interaction between these ions. The analysis of the absorption curve and its first derivative allowed to obtain several magnetic parameters including the number of spins N participating in EPR resonance which showed a decrease with increasing temperature and the activation energy Ea, which experienced a decrease with x.