EPR studies for GdBa2Cu3O7-δ added with nanosized ferrite CoFe2O4

EPR measurements were conducted at different temperatures 100K <= T <= 295K for GdBa2Cu3O7-delta 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 approximate to 2 is detected for the (CoFe2O4)(x)GdBa2Cu3O7-delta 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 E-a, which experienced a decrease with x.