INTERPRETATION OF THE MAGNETIC SPECIFIC-HEAT OF OXYGEN-DEFICIENT AND DOPED NDBA2CU3OX AND DYBA2CU3OX COMPOUNDS

In contrast to NdBa2Cu3Ox samples with x close to 7 and 6 which according to neutron diffraction and specific heat measurements exhibits long-range antiferromagnetic ordering of the Nd3+ ions, only short-range magnetic ordering has been found in the intermediate oxygen range 6.9 greater than or similar to x greater than or similar to 6.6. The short-range ordering behavior of the magnetic specific heat is neither of one-dimensional chain-type nor two-dimensional XY or Heisenberg type, but could be explained by two-dimensional Heisenberg spin-1/2 clusters. A two-dimensional Ising cluster model was applied to DyBa2Cu3Ox in order to account for the high single ion anisotropy of Dy3+; this model reproduces the zero magnetic field specific heat data but does not agree as well as the Heisenberg model with the data taken in an external magnetic field.