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

In quasi-two-dimensional (quasi-2D) quantum magnets, the ratio of Neel temperature T-N to Curie-Weiss temperature Theta(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 = Theta(CW)/T-N may be used as measure of frustration strength in the quasi-2D quantum magnets.