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Samples of Y1−x Ca x Sr2GaCu2O7−δ (x=0, 0.4) doped with57Fe, prepared 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 thex=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 temperatures. At temperatures above 90 K, these iron ions display a pure quadrupole doublet Mossbauer spectrum. The samplex=0.4 also displays magnetic order of the Cu(2) site,T N≈370 K. A sharp drop in the hyperfine field is observed atT N, probably associated with a first-order phase transition or two-dimensional ordering. The iron nuclei in the Ga site display paramagnetic long spin relaxation time phenomena at 4.2 K. Thex=0.4 sample prepared under 110 atm oxygen pressure, displays superconductivity,T c≈50 K. The Mossbauer spectra give evidence of the presence of two phases. One displays magnetic order, the other is paramagnetic, the last is probably associated with the superconducting phase. |
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