Using the Oguchi approximation, we have examined the magnetic properties of a mixed-spin (1/2, 1) XXZ Heisenberg model with a crystal field. The focus is on the 3D Heisenberg system, for which the phase diagrams and magnetizations are obtained numerically. It is found that the model features second- and first-order phase transition lines, as well as tricritical and critical end-points. The critical behavior is discussed and compared with previous works on Heisenberg systems.

Romanian Journal of PhysicsMar 15, 20254 citations

Cienc. Cult. (Sao Paulo) Supl

The reaction field approximation applied to the Heisenberg model in the ordered phase and phase diagram

M. A. Gusmão, Claudio Scherer

Published Jan 1, 1977• 0 citations

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{\mathit{T}}_{\mathit{c}}

\ensuremath{\sim}exp[-

{\mathit{H}}^{2}

/(2

{\mathit{J}}^{2}

{\mathit{S}}^{2}

)], as compared with

{\mathit{T}}_{\mathit{c}}

\ensuremath{\sim}exp{-

{\mathit{H}}^{2}

/[2

{\mathit{J}}^{2}

S(S+1)]} for classical spins of magnitude \ensuremath{\surd}S(S+1) . In the case of QXYSG in a transverse field (\ensuremath{\Gamma}), the phase boundary terminates at \ensuremath{\Gamma}/J=2 for T=0.