Zigzag antiferromagnetic ground state with anisotropic correlation lengths in the quasi-two-dimensional honeycomb lattice compound Na2Co2TeO6

A. K. Bera, S. M. Yusuf, Amit Kumar, and C. Ritter
Phys. Rev. B 95, 094424 – Published 20 March 2017

Abstract

The crystal structure, magnetic ground state, and the temperature-dependent microscopic spin-spin correlations of the frustrated honeycomb lattice antiferromagnet Na2Co2TeO6 have been investigated by powder neutron diffraction. A long-range antiferromagnetic (AFM) ordering has been found below TN24.8K. The magnetic ground state, determined to be zigzag antiferromagnetic and characterized by a propagation vector k=(1/200), occurs due to the competing exchange interactions up to third-nearest neighbors within the honeycomb lattice. The exceptional existence of a limited magnetic correlation length along the c axis (perpendicular to the honeycomb layers in the ab planes) has been found even at 1.8 K, well below the TN24.8K. The observed limited correlation along the c axis is explained by the disorder distribution of the Na ions within the intermediate layers between honeycomb planes. The reduced ordered moments mCo(1)=2.77(3)μB/Co2+ and mCo(2)=2.45(2)μB/Co2+ at 1.8 K reflect the persistence of spin fluctuations in the ordered state. Above TN24.8K, the presence of short-range magnetic correlations, manifested by broad diffuse magnetic peaks in the diffraction patterns, has been found. Reverse Monte Carlo analysis of the experimental diffuse magnetic scattering data reveals that the spin correlations are mainly confined within the two-dimensional honeycomb layers (ab plane) with a correlation length of 12Å at 25 K. The nature of the spin arrangements is found to be similar in both the short-range and long-range ordered magnetic states. This implies that the short-range correlation grows with decreasing temperature and leads to the zigzag AFM ordering at TTN. The present study provides a comprehensive picture of the magnetic correlations over the temperature range above and below the TN and their relation to the crystal structure. The role of intermediate soft Na layers on the magnetic coupling between honeycomb planes is discussed.

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  • Received 26 August 2016
  • Revised 22 December 2016

DOI:https://doi.org/10.1103/PhysRevB.95.094424

©2017 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

A. K. Bera, S. M. Yusuf*, and Amit Kumar

  • Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India

C. Ritter

  • Institut Laue-Langevin, 71 Avenue des Martyrs, 38000 Grenoble, France

  • *smyusuf@barc.gov.in

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Issue

Vol. 95, Iss. 9 — 1 March 2017

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