MAGNETIC-PROPERTIES - MOSSBAUER, X-RAY-ABSORPTION SPECTROSCOPY, AND SPECIFIC-HEAT STUDIES OF PR(1.5)CE(0.5)MSR(2)CU(2)O(Z) (M=TA, IN, NB, NB+GA) COMPOUNDS

We have investigated Pr(1.5)Ce(0.5)MSr(2)Cu(2)O(z) (z=9 or 10) materia ls (M=Ta, In, and NbSGa) by complementary experimental techniques. All materials studied are not superconducting. Magnetic susceptibility st udies for M=Ta reveal one magnetic anomaly at 23 K and irreversibility phenomena at higher temperatures. The presence of 0.5% Fe-57 dramatic ally affects the positions of the anomalies, and Mossbauer spectroscop y studies (MS) reveal that the Cu(2) sites are magnetically ordered be low T-N(Cu)=130 K. This low T-N(Cu) obtained is discussed. No specific heat anomaly was observed at 23 K, suggesting that the Pr sublattice does not order magnetically, and the anomalies in the susceptibility o riginate from the Cu moments. No anomalies in the susceptibility curve s are found for M=In and Nb+Ga compounds. However, MS indicate that fo r the mixed compound, the Cu sites are magnetically ordered at low tem peratures. The magnetic behavior of M=Ta is compared to similar system s with two anomalies for M=Nb at 11 and 52 K, and three anomalies for M=Ga at 12, 52, and 94 K. X-ray absorption spectroscopy (XAS) indicate s that in all materials studied, the Pr has a mixed valence close to 3 . The Pr valence does not change with temperature.