Neel temperature and reentrant H-T phase diagram of quasi-2D frustrated magnets

In quasi-2D quantum magnets the ratio of Neel temperature $T_text N$ to Curie-Weiss temperature $Theta_text{CW}$ 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 $T_text N$ 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 $T_text N(H)$ and the associated possible reentrance behavior of the ordered moment due to quantum fluctuations is 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 $f=Theta_text{CW}/T_text N$ may be used as measure of frustration strength in the quasi-2D quantum magnets.