DOI: https://doi.org/10.30970/jps.02.391
THERMODYNAMICS OF XXZ-MODEL WITHIN TWO-PARTICLE CLUSTER APPROXIMATION
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Journal of Physical Studies 2(3), 391–400 (1998)
DOI: https://doi.org/10.30970/jps.02.391 THERMODYNAMICS OF XXZ-MODEL WITHIN TWO-PARTICLE CLUSTER APPROXIMATION |
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R. R. Levitskii, S. I. Sorokov, O. R. Baran, I. M. Pyndsyn
Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine,
1 Svientsitskii Str., Lviv, 290011, Ukraine
Phone: 42–74–39, e–mail: sorok@icmp.lviv.ua
The XXZ–model was investigated within two–particle cluster approximation with two variational parameters $φ^z$, $φ^x$. The long–range interaction $J$ was taken into account in the framework of mean–field approximation.
At various values of the anisotropy parameter $\ani$ ($K^{zz}=γ K$, $K^{xx}=K^{yy}=α K$, $J^{zz}=γ J$, $J^{xx}=J^{yy}=α J$, $K$ — short–range interaction) and long–range interaction $J$, phase diagrams were constructed and temperature dependences of $\langle S^z \rangle$, $\langle S^x \rangle$, entropy, specific heat, and static susceptibility were calculated. It was shown that at $\ani \geq 1$ two–particle cluster approximation gave qualitatively incorrect results in a low–temperature region.