Quasi-one-dimensional uniform spin-1/2 Heisenberg antiferromagnet KNaCuP2O7 probed by 31P and 23Na NMR

Quasi-one-dimensional uniform spin-1/2 Heisenberg antiferromagnet KNaCuP2O7 probed by 31P and 23Na NMR
S. Guchhait,1 Qing-Ping Ding ,2 M. Sahoo,3 A. Giri,4 S. Maji,4 Y. Furukawa ,2 and R. Nath 1 *

1School of Physics, Indian Institute of Science Education and Research, Thiruvananthapuram 695551, India
2Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
3Department of Physics, University of Kerala, Kariavattom, Thiruvananthapuram 695581, India
4 School of Physical Sciences, Indian Association for the Cultivation of Science, Kolkata 700032, India

The Cu2+ ions-based spin chain compounds have drawn particular interest mainly due to low spin value and large value of exchange couplings. Many Cu2+ based S =1/2 chain systems have been extensively studied. Among them, a well-known family is A2CuP2O7 (A = Na, Li, and K) compounds, although they have different crystal structures. KNaCuP2O7 has monoclinic structure with space group P21/n. [1]. CuO4 plaquettes are corner shared with four PO4 tetrahedra forming isolated magnetic chains stretched along a direction. The adjacent chains are weakly coupled by frustrated interchain couplings. The polycrystalline sample of KNaCuP2O7 was synthesized by the solid-state synthesis method. The magnetic properties of this compound investigated in great detail by temperature (T) dependent x-ray diffraction, magnetization, specific heat (Cp), and local probe technique 31P and 23Na nuclear magnetic resonance (NMR) measurements and complementary electronic structure calculations. No evidence of magnetic long-range order (LRO) was found down to 2 K in magnetic susceptibility (ꭓ(T)) and specific heat (Cp) measurements. The temperature-dependent magnetic susceptibility and 31P NMR shift could be modeled very well by the uniform spin-1/2 Heisenberg antiferromagnetic (HAF) chain model (Johnston model) with a nearest-neighbour (NN) interaction J/kB ≈ 58.7 K. [2] The first-principles electronic structure calculations support the picture of a S=1/2 HAF uniform chain with JDFT/kB ≈ 59 K and negligibly small interchain couplings. The sharp increase of NMR spin-lattice relaxation rates (311/T1 and 231/T1) implies the expected magnetic LRO at around TN ≈ 1 K. From the expected value of TN, the average interchain coupling is estimated to be J┴ /kB ≈ 0.28 K. [3] Moreover, the NMR spin-lattice relaxation rates show the dominant contributions from uniform (q = 0) and staggered (q = ± π/a) spin fluctuations in the high- and low-temperature regimes, respectively, mimicking one-dimensionality of the spin lattice. We have also demonstrated that 311/T1 in high temperatures varies linearly with 1/√H, reflecting the effect of spin diffusion on the dynamic susceptibility due to the long-wavelength (q ∼ 0) spin fluctuations.[4]

[1] I. Fitouri and H. Boughzala, Acta Crystallogr. Sect. E 74, 109 (2018).
[2] Johnston et al, Phys. Rev. B 61, 9558 (2000).
[3] Johannes et al, Phys. Rev. B 74, 174435 (2006).
[4] F. Borsa and M. Mali, Phys. Rev. B 9, 2215 (1974).

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