COMPARISON BETWEEN THE MAGNETIC SPECIFIC-HEAT OF NDBA2CU3OX AND DYBA2CU3OX

Low temperature heat-capacity measurements have been performed to study the magnetic ordering in NdBa2Cu3Ox and DyBa2Cu3Ox. In order to investigate the type of ordering, magnetic fields up to 6 T and hydrostatic pressures up to 4.5 kbar were applied. While for NdBa2Cu3Ox and DyBa2Cu3Ox both the fully oxidized and the fully oxygen reduced samples display long rang antiferromagnetic ordering, only magnetic short range interaction could be found for samples in an intermediate range of oxygen concentration. For NdBa2Cu3Ox, where superexchange is believed to be the dominant magnetic interaction, T-N is three times higher in the sample with x = 6.26 compared to the one with x = 6.98. In contrast, T-N of DyBa2Cu3Ox is almost oxygen independent as expected for this mainly dipolar interacting system.