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

Magnetic properties of SrCuP2O7 and PbCu1-xZn,P2O7 (x = 0, 0.1, and 0.5) were studied by magnetic susceptibility, chi(T), and specific heat, C-p(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 chi(T) data were fitted by the Bonner-Fisher curve (plus temperature independent and Curie-Weiss terms) with g = 2.20 and J/k(B) = 9.38 K for SrCuP2O7 and g = 2.17 and J/k(B) = 8.41 K for PbCuP2O7 (Hamiltonian H = JSigmaS(i)S(i+1)). Magnetic specific heat, C-m(T), exhibited one broad maximum due to short-range ordering and one sharp peak at T-N = 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 C-m,( curves (C-max and T-max(C)) 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 1 D uniform chain model but those of PbCu0.5Zn0.5P2O7 did not. In air, SrCuP207 was stable at least up to 1373 K while PbCuP2O7 melted incongruently above 1180 K.