Neel temperature and reentrant H-T phase diagram of quasi-two-dimensional frustrated magnets

摘要

In quasi-two-dimensional (quasi-2D) quantum magnets, the ratio of Neel temperature T_N to Curie-Weiss temperature Θ_(CW) is frequently used as an empirical criterion to judge the strength of frustration. In this work, we investigate how these quantities are related in the canonical quasi-2D frustrated square or triangular J_1-J_2 model. Using the self-consistent Tyablikov approach for calculating T_N we show their dependence on the frustration control parameter J_2/J_1 in the whole Neel and columnar antiferromagnetic phase region. We also discuss approximate analytical results. In addition, the field dependence of T_N(H) and the associated possible reentrance behavior of the ordered moment due to quantum fluctuations are investigated. These results are directly applicable to a class of quasi-2D oxovanadate antiferromagnets. We give clear criteria to judge under which conditions the empirical frustration ratio f = Θ_(CW) / T_N may be used as measure of frustration strength in the quasi-2D quantum magnets.