Journal of Physical Studies 5(3/4), 341–348 (2001) DOI: https://doi.org/10.30970/jps.05.341 MEAN FIELD ANALYSIS OF TWO COUPLED HEISENBERG MODELS D. V. Shopova1, T. L. Boyadjiev2 1CPCM Laboratory, G. Nadjakov Institute of Solid State Physics Bulgarian Academy of Sciences, BG–1784 Sofia, Bulgaria 2Faculty of Mathematics and Computer Science, University of Sofia BG–1164 Sofia, Bulgaria

We have derived and analyzed the Landau free energy for two coupled Heisenberg subsystems in the general case of $n$-component order parameters. The calculation was done in the weak-coupling limit when the exchange interactions $J_{1}$ and $J_{2}$ in the subsystems exceed the intersubsystem interaction $K$. There exist two stable collinear phases, depending on the sign of $K$. The phase transitions to the stable phases are of second order for the whole range of parameters of the model under consideration. The numerical calculations show that for positive sign of interactions two more phases exist, which are metastable or unstable depending on the number of the order parameter components $n$.

PACS number(s): 75.10.Hk,75.30.Kz,75.40.Cx

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