Acoustic and magnetic anomalies near the saturation field of the S=1/2 antiferromagnetic Heisenberg chain studied on a Cu(II) coordination polymer - art. no. 092403

By means of magnetic measurements as a function of temperature and magnetic field, the coordination polymer Cu(II)-2,5-bis(pyrazol-1-yl)-1,4-dihydroxybenzene has been identified as a model system for a homogeneous antiferromagnetic S=1/2 Heisenberg spin chain with a moderate exchange-coupling constant |J| = 21.5 K/k_B. Measurements of the longitudinal elastic constant in pulsed fields up to 50 T, i.e., across the saturation field gmu(B)B(S)=2|J|, reveal a pronounced acoustic anomaly near B_S at T<|J|k_B. We show that this feature is directly related to the shape of the magnetization curve and thus represents a generic property of a one-dimensional S=1/2 Heisenberg antiferromagnet with finite spin-lattice interaction.