EPR STUDY OF INTERACTION BETWEEN PARAMAGNETIC SPECIES AND THE FINE PARTICLES OF THE R-BA-CU-O (R = Y,EU,GD) SUPERCONDUCTORS

An approach to the characterization of the high-Tc fine particles was presented with an electron spin resonance (ESR) method on powder mixtures of high-Tc cuprates and paramagnetic species. ESR absorption by Cr(3+) was obtained with a powder mixture of the Cr doped MgO and the ground high-Tc cuprates: R-Ba-Cu-O (R = Y, Eu, Gd). Line broadening of the ESR spectra has been observed at temperature lower than Tc of the bulk oxide which indicates a decrease of Tc of the fine particles.