MAGNETISM AND SUPERCONDUCTIVITY IN Y1-XCAXSR2GACU2O7-DELTA

Samples of Y1-xCaxSr2GaCu2O7-delta (x=0, 0.4), prepared under various oxygen pressures, have been studied by magnetometry. Samples doped wit h Fe-57 have been studied also by Mossbauer spectroscopy. The majority of the iron ions (Fe 3+) enters the Ga (Cu(1)) site, a minority enter s the Cu(2) site. For the x=0 sample, the Mossbauer spectra of the iro n nuclei in the Cu(2) sublattice display magnetic order of the Cu with T(N)=370 K. The moments order along the c-axis. The iron in the Ga si te diplays magnetic order only at low temperatures, probably induced f rom the Cu(2) site. At temperatures above 90 K, these iron ions displa y a single pure quadrupole doublet Mossbauer spectrum, with a splittin g of 2.0 mm/s. The sample x=0.4 prepared under ambient pressure of oxy gen (APO) also displays magnetic order of the Cu(2) site, with T(N) al most-equal-to 370 K. The iron nuclei in the Ga site display paramagnet ic long spin relaxation times phenomena at 4.2 K. The x=0.4 sample, pr epared under 110 atm oxygen pressure (HPO), displays superconductivity according to the magnetometry measurements (T(c) almost-equal-to 50 K ). The Mossbauer spectra give evidence of the presence of two phases i n this sample. One displays magnetic order like the APO sample, the ot her is paramagnetic. The latter is probably associated with the superc onducting phase.