Characterization of quasi-one-dimensional S=1/2 Heisenberg anti ferromagnets Sr2Cu(PO4)2 and Ba2Cu(PO4)2 with magnetic susceptibility, specific heat, and thermal analysis

Properties of Sr2Cu(PO4)(2) and Ba2Cu(PO4)(2) having [Cu(PO4)(2)](infinity) linear chains in their structures with Cu-O-P-O-Cu linkages were studied by magnetic susceptibility (T = 2-400 K, H = 100 Oe) and specific heat measurements (T = 0.45-21 K). Magnetic susceptibility versus temperature curves, chi(T), showed broad maxima at T-M = 92 K for Sr2Cu(PO4)(2) and T-M = 82 K for Ba2Cu(PO4)(2) characteristic of quasi-one-dimensional systems. The chi(T) data were excellently fitted by the spin susceptibility curve for the uniform S 1/2 chain (Plus temperature-independent and Curie-Weiss terms) with g = 2.153(4) and J/k(B) = 143.6(2) K for Sr2Cu(PO4)(2) and g = 2.073(4) and J/k(B) = 132.16(9) K for Ba2Cu(PO4)(2) (Hamiltonian H = JSigmaS(i)S(i+1)). The similar J/k(B) values were obtained from the specific heat data. No anomaly was observed on the specific heat from 0.45 to 21 K for both compounds indicating that the temperatures of long-range magnetic ordering, T-N, were below 0.45 K. Sr2Cu(PO4)(2) and Ba2Cu(PO4)(2) are an excellent physical realization of the S = 1/2 linear chain Heisenberg antiferromagnet with k(B)T(N)/J<0.34% together with Sr2CuO3 (k(B)T(N)/ J approximate to 0.25%) and gamma-LiV2O5 (k(B)T(N)/J<0.16%). Sr2Cu(PO4)(2) and Ba2Cu(PO4)(2) were stable in air up to 1280 and 1150 K, respectively. (C) 2003 Elsevier Inc. All rights reserved.