Abstract
We present observations of highly frustrated quasi-two-dimensional (2D) magnetic correlations in the honeycomb lattice layers of the Seff =1/2 compound γ-BaCo2(PO4)2 (γ-BCPO). Specific heat shows a broad peak comprised of two weak kink features at TN1∼6 K and TN2∼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 TN1 and TN2, at which two separate, incompatible, short range magnetic orders onset: commensurate antiferromagnetic correlations with correlation length ξc=60±2 Å (TN1) and in quasi-2D helical domains with ξh=350±11 Å (TN2). 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 J1-J2-J3 model with ferromagnetic nearest-neighbor exchange J1 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. These data show that γ-BCPO is a rare highly frustrated, quasi-2D Seff =1/2 honeycomb lattice material which resists long range magnetic order and spin freezing.
| Original language | English |
|---|---|
| Article number | 134409 |
| Journal | Physical Review B |
| Volume | 97 |
| Issue number | 13 |
| DOIs | |
| State | Published - Apr 12 2018 |
Funding
We acknowledge J. R. Neilson, A.E. Maughan, J. Kurzman, and S. Folkman for assistance with sample preparation, and R. Moessner for helpful discussions. We acknowledge the support of the National Institute of Standards and Technology, US Department of Commerce, as well as Oak Ridge National Laboratory, US Department of Energy, in providing the neutron research facilities used in this work. We acknowledge the support of Argonne National Laboratory, US Department of Energy, in providing the synchrotron facility used in this work. This research was supported by the National Science Foundation Agreement No. DMR-1611217.