Study of one-dimensional nature of S=12 (Sr,Ba)2Cu(PO4)2 and BaCuP2O7 via P31 NMR

R. Nath, A. V. Mahajan, N. Büttgen, C. Kegler, A. Loidl, and J. Bobroff
Phys. Rev. B 71, 174436 – Published 31 May 2005

Abstract

The magnetic behavior of the low-dimensional phosphates (Sr,Ba)2Cu(PO4)2 and BaCuP2O7 was investigated by means of magnetic susceptibility and P31 nuclear magnetic resonance (NMR) measurements. We present here the NMR shift, the spin-lattice (1T1), and spin-spin (1T2) relaxation-rate data over a wide temperature range 0.02KT300K. The temperature dependence of the NMR shift K(T) is well described by the S=12 Heisenberg antiferromagnetic chain model [D. C. Johnston, R. K. Kremer, M. Troyer, X. Wang, A. Klümper, S. L. Bud’ko, A. F. Panchula, and P. C. Canfield, Phys. Rev. B 61, 9558 (2000)] with an intrachain exchange of JkB165, 151, and 108K in Sr2Cu(PO4)2, Ba2Cu(PO4)2, and BaCuP2O7, respectively. Deviations from Johnston’s expression are seen for all these compounds in the T dependence of K(T) at low temperatures. P31 is located symmetrically between the Cu ions and fluctuations of the staggered susceptibility at q=πa should be filtered out due to vanishing of the geometrical form factor. However, the qualitative temperature dependence of our P31 NMR 1T1 indicates that relaxation due to fluctuations around q=πa (but πa) have the same T dependence as those at q=πa and apparently dominate. Our measurements suggest the presence of magnetic ordering at 0.85K in BaCuP2O7 (JkB108K) and a clear indication of a phase transition (divergence) in 1T1(T), 1T2(T), and a change of the line shape is observed. This enables us to investigate the one-dimensional (1D) behavior over a wide temperature range. We find that 1T1 is nearly T independent at low temperatures (1KT10K), which is theoretically expected for 1D chains when relaxation is dominated by fluctuations of the staggered susceptibility. At high temperatures, 1T1 varies nearly linearly with temperature, which accounts for contribution of the uniform susceptibility.

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  • Received 25 August 2004

DOI:https://doi.org/10.1103/PhysRevB.71.174436

©2005 American Physical Society

Authors & Affiliations

R. Nath and A. V. Mahajan

  • Department of Physics, Indian Institute of Technology, Mumbai 400076, India

N. Büttgen, C. Kegler, and A. Loidl

  • Experimentalphysik V, Elektronische Korrelationen und Magnetismus, Institut für Physik, Universität Augsburg, D-86135 Augsburg, Germany

J. Bobroff

  • Laboratoire de Physique des Solides, Universite Paris-Sud, 91405 Orsay, France

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Vol. 71, Iss. 17 — 1 May 2005

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