Collinear antiferromagnetic phases of a frustrated spin-½ J1J2J1 Heisenberg model on an AA-stacked bilayer honeycomb lattice

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The regions of stability of two collinear quasiclassical phases within the zero-temperature quantum phase diagram of the spin-½ J1J2J1 model on an
AA-stacked bilayer honeycomb lattice are investigated using the coupled cluster method (CCM).  The model comprises two monolayers in each of which the spins, residing on honeycomb-lattice sites, interact via both nearest-neighbor (NN) and frustrating next-nearest-neighbor isotropic antiferromagnetic (AFM) Heisenberg exchange interactions, with respective strengths J1 > 0 and J2 ≡ κJ1 > 0.  The two layers are coupled via a comparable Heisenberg exchange interaction between NN interlayer pairs, with a strength J1≡ δJ1.  The complete phase boundaries of two quasiclassical collinear AFM phases, namely the Néel and Néel-II phases on each monolayer, with the two layers coupled so that NN spins between them are antiparallel, are calculated in the κδ half-plane with κ > 0.  Whereas on each monolayer in the Néel state all NN pairs of spins are antiparallel, in the Néel-II state NN pairs of spins on zigzag chains along one of the three equivalent honeycomb-lattice directions are antiparallel, while NN interchain spins are parallel.  We calculate directly in the thermodynamic (infinite-lattice) limit both the magnetic order parameter M and the excitation energy ∆ from the szT= 0 ground state to the lowest-lying |szT| = 1 excited state (where szis the total z component of spin for the system as a whole, and where the collinear ordering lies along the direction), for both quasiclassical states used (separately) as the CCM model state, on top of which the multispin quantum correlations are then calculated to high orders (n ≤ 10) in a systematic series of approximations involvingn-spin clusters.  The sole approximation made is then to extrapolate the sequences of nth-order results for M and ∆ to the exact limit, n → ∞.

Bibliographical metadata

Original languageEnglish
Pages (from-to)262-273
Number of pages12
JournalJournal of Magnetism and Magnetic Materials
Early online date8 Mar 2019
Publication statusPublished - 2019