SUPERCONDUCTIVITY AND MAGNETISM IN Y1-XCAXSR2GACU2O7-DELTA

Samples of Y1-xCaxSr2GaCu2O7-delta (x = 0, 0.4) doped with Fe-57, prep ared under various oxygen pressures, have been studied by magnetometry and Mossbauer spectroscopy. Most of the iron ions (Fe3+) enter the Ga (Cu(1)) site. For the x = 0 sample, the Mossbauer spectra of the iron nuclei in the Cu(2) sublattice display magnetic order of Cu, T-N = 370 K. The iron ions in the Ga site display magnetic order only at low te mperatures. At temperatures above 90 K, these iron ions display a pure quadrupole doublet Mossbauer spectrum. The sample x = 0.4 also displa ys magnetic order of the Cu(2) site, T-N approximate to 370 K. A sharp drop in the hyperfine field is observed at T-N, probably associated w ith a first-order phase transition or two-dimensional ordering. The ir on nuclei in the Ga site display paramagnetic long spin relaxation tim e phenomena at 4.2 K. The x = 0.4 sample prepared under 110 atm oxygen pressure, displays superconductivity, T-c approximate to 50 K. The Mo ssbauer spectra give evidence of the presence of two phases. One displ ays magnetic order, the other is paramagnetic, the last is probably as sociated with the superconducting phase.