Abstract
We present a spin-rotation-invariant Green-function theory for the dynamic spin susceptibility in the spin-1/2 antiferromagnetic Heisenberg model on a stacked honeycomb lattice. Employing a generalized mean-field approximation for arbitrary temperatures, the thermodynamic quantities (two-spin correlation functions, internal energy, magnetic susceptibility, staggered magnetization, Néel temperature, correlation length) and the spin-excitation spectrum are calculated by solving a coupled system of self-consistency equations for the correlation functions. The temperature dependence of the magnetic (uniform static) susceptibility is ascribed to antiferromagnetic short-range order. The Néel temperature is calculated for arbitrary interlayer couplings. Our results are in a good agreement with numerical computations for finite clusters and with available experimental data on the β-Cu2V2O2 compound.
Highlights
We present a spin-rotation-invariant Green-function theory for the dynamic spin susceptibility in the spin-1/2 antiferromagnetic Heisenberg model on a stacked honeycomb lattice
In this paper we present a theory of magnetic order in the honeycomb antiferromagnetic Heisenberg model (AFHM) over the whole temperature region that is based on the calculation of the dynamic spin susceptibility (DSS) within the spin-rotation-invariant (SRI) relaxation-function theory [22,23,24] using the generalized mean-field approximation (GMFA), as has been done in our study of the compass-Heisenberg model on the square lattice [25]
To evaluate the spin-excitation spectrum and the thermodynamic properties, the correlation functions CR,αβ and the vertex parameters α1, α2, and αz appearing in the spectrum ω±(q) as well as the condensation term C
Summary
For the isotropic 2D honeycomb Heisenberg model with nn AF interaction, the LRO at zero temperature, similar to the square lattice, was confirmed in a number of studies mostly performed for finite-lattice systems. Analytical approaches which are capable to evaluate the thermodynamics of the AFHM on the layered honeycomb lattice both in the AF phase and in the paramagnetic phase with a temperature-dependent AF short-range order (SRO) are desirable. To this end, in this paper we present a theory of magnetic order in the honeycomb AFHM over the whole temperature region that is based on the calculation of the dynamic spin susceptibility (DSS) within the spin-rotation-invariant (SRI) relaxation-function theory [22,23,24] using the generalized mean-field approximation (GMFA), as has been done in our study of the compass-Heisenberg model on the square lattice [25].
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