Type-II order in face-centered-cubic Heisenberg antiferromagnets

Abstract

The problem of determining the phase diagram for type-II fcc Heisenberg antiferromagnets with first- and second-neighbor exchange is treated with a variety of methods. In addition to comparison with known results of the mean-field approximation and the random-phase approximation, the series expansion of the staggered susceptibility is reexamined, and a new calculation based on a modified Callen decoupling (MCD) is presented. The existence of large anomalies, previously found in the Padé results, is shown to be highly questionable. The MCD results support the assumption that the corrections to RPA are "regular," although a new anomaly in the Néel temperature is found for $\left|J_1\right|\ll \left|J_2\right|$. Excellent agreement between the MCD results and the experimental Néel temperature for EuTe is found.