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Title: Short-range order in the quantum XXZ honeycomb lattice material BaCo 2 ( PO 4 ) 2

In this paper, we present observations of highly frustrated quasi-two-dimensional (2D) magnetic correlations in the honeycomb lattice layers of the S eff =1/2 compound γ-BaCo 2(PO 4) 2 (γ-BCPO). Specific heat shows a broad peak comprised of two weak kink features at T N1~6 K and T N2~3.5 K, the relative weights of which can be modified by sample annealing. Neutron powder diffraction measurements reveal short range quasi-2D order that is established below T N1 and T N2, at which two separate, incompatible, short range magnetic orders onset: commensurate antiferromagnetic correlations with correlation length ξ c=60±2 Å (T N1) and in quasi-2D helical domains with ξ h=350±11 Å (T N2). The ac magnetic susceptibility response lacks frequency dependence, ruling out spin freezing. Inelastic neutron scattering data on γ-BCPO is compared with linear spin wave theory, and two separate parameter regions of the XXZ J 1-J 2-J 3 model with ferromagnetic nearest-neighbor exchange J 1 are favored, both near regions of high classical degeneracy. High energy coherent excitations (~10 meV) persist up to at least 40 K, suggesting strong in-plane correlations persist above TN. Finally, these data show that γ-BCPO is a rare highly frustrated, quasi-2D S eff =1/2 honeycomb latticemore » material which resists long range magnetic order and spin freezing.« less
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  1. Colorado State Univ., Fort Collins, CO (United States). Department of Physics
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Neutron Scattering Division
  3. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
  4. Colorado State Univ., Fort Collins, CO (United States). Department of Physics; Canadian Institute for Advanced Research (CIFAR), Toronto, Ontario (Canada). Quantum Materials Program
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 97; Journal Issue: 13; Journal ID: ISSN 2469-9950
American Physical Society (APS)
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1432902