Short-range order in the quantum XXZ honeycomb lattice material BaCo2(PO4)2

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 ξ h = 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. arXiv:1712.06208v2 [cond-mat.str-el]

Kitaev Spin Liquid in 3d Transition Metal Compounds

“…At very large |∆/λ| > 10, one observes K ∼ 0 and Γ Γ . In this limit, bond-directional nature is quenched by the crystal field, and the model becomes similar to a conventional XXZ model which was commonly adopted to analyze the experimental data in Co 2+ compounds 57,87,88,89,90,91 .…”

“…Honeycomb lattice cobaltates.-A number of such compounds are known: A 3 Co 2 SbO 6 (A ¼ Na; Ag; Li) [18][19][20]43,44], Na 2 Co 2 TeO 6 [18,[45][46][47], BaCo 2 ðXO 4 Þ 2 (X ¼ As, P) [48][49][50][51], CoTiO 3 [52][53][54], CoPS 3 [55,56]. They are quasi-two-dimensional magnets; within the ab planes, zigzag or FM order is most common.…”

“…Traditionally, experimental data in Co 2þ compounds is analyzed in terms of an effectiveS ¼ 1=2 models of XXZ type [48,50,54,[57][58][59]. AsS ¼ 1=2 magnons (∼10 meV) are well separated from higher lying spin-orbit excitations (∼30 meV), the pseudospin picture itself is well justified; however, a conventional XXZ model neglects the bonddirectional nature of pseudospinS ¼ 1=2 interactions.…”

Kitaev interactions in the Co honeycomb antiferromagnets Na3Co2SbO6 and Na2Co2Songvilay1, Robert2, Petit3 et al. 2020Phys. Rev. B968561View full textAdd to dashboardCite

“…The experimental spectra were also compared against a Heisenberg X X Z model comprising first, second, and third nearest-neighbor couplings (J 1 -J 2 -J 3 model) [53]:…”

Van Hove singularity in the magnon spectrum of the antiferromagnetic quantum honeycomb lattice

“…In the opposite limit of isotropic spin interactions, frustrated quantum magnetism can arise through the competition of nearest neighbor and nextnearest neighbor interactions [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] . Indeed, most honeycomb lattice materials studied thus far require the addition of further neighbor interactions to explain the underlying physical behavior 6,8,[38][39][40][41][42][43][44][45][46][47] . Such materials, with a complicated phase diagram as a function of first, second, and third nearest-neighbor interactions, have been fertile ground for exploration.…”