Short-range and long-range magnetic ordering in SrCuP2O7 and PbCuP2O7.

Magnetic properties of SrCuP2O7 and PbCu(1-x)ZnxP2O7 (x=0, 0.1, and 0.5) were studied by magnetic susceptibility, chiT, and specific heat, Cp(T). Both data showed that magnetism of SrCuP2O7 and PbCuP2O7 can be described by the one-dimensional (1D) uniform chain model despite the structural features suggesting the presence of zigzag chains with next-nearest-neighbor interactions. The chiT data were fitted by the Bonner-Fisher curve (plus temperature independent and Curie-Weiss terms) with g=2.20 and J/kB=9.38 K for SrCuP2O7 and g=2.17 and J/kB=8.41 K for PbCuP2O7 (Hamiltonian H=J SigmaSiS(i+1)). Magnetic specific heat, Cm(T), exhibited one broad maximum due to short-range ordering and one sharp peak at TN=1.64 K for SrCuP2O7 and TN=1.15 K for PbCuP2O7 due to long-range antiferromagnetic ordering. The characteristic values of the broad maxima on the Cm(T) curves (Cmax and TC(max)) were in good agreement with the theoretical calculations for the uniform 1D S=1/2 Heisenberg chain. Magnetic properties of PbCu0.9Zn0.1P2O7 still obeyed the 1D uniform chain model but those of PbCu0.5Zn0.5P2O7 did not. In air, SrCuP2O7 was stable at least up to 1373 K while PbCuP2O7 melted incongruently above 1180 K.