Crossover from two-dimensional to three-dimensional magnetic structure in Pr1.5Ce0.5Sr2GaCu2O9

We investigated Pr1.5Ce0.5Sr2GaCu2O9 (PrCeSGCO) by several complementary experimental techniques. PrCeSGCO is not superconducting and the magnetic susceptibility data reveal three magnetic anomalies at 12, 54, and 94 K. While the anomalies always appear together, only the two first peaks are sensitive to oxygen concentration. The presence of 0.5% Fe dramatically affects the 54-K peak and shifts it to 67 K, and Mössbauer studies indicate that the transition at TN(Cu)=94 K is related to antiferromagnetic ordering of the Cu sublattice. A strong two-dimensional quantum spin fluctuation is assumed as the cause of the peak at 94 K. The peak in the susceptibility at 54 K is probably the crossover to a three-dimensional magnetic structure and the peak at 12 K is due to spin reorientation of Cu moments. While the anomalies are clearly identified by magnetic measurements, no specific-heat anomaly was observed at either temperature. A high linear term of 111 mJ/mol(Pr) K2 is obtained in the specific heat of the oxygen-deficient PrCeSGCO material.