Magnetic specific heat of the honeycomb lattice of spin one-half with anisotropic Heisenberg exchange by a new method

The magnetic specific heat of the honeycomb lattice of S = 12 Heisenberg spin with anisotropic exchange is calculated by using the new approximation method reported in a previous paper. In the spin system with the anisotropy parameter |γ|<1 (Ising-Heisenberg system), the specific heat shows a similar divergence as that of the pure Ising spin system, namely a logarithmic divergence at the critical temperature. The same approximation is also applied to the spin system with |γ|>1 (Heisenberg XY system), showing a divergence of the same kind.