Self-consistent spin-wave theory of layered Heisenberg magnets

The versions of the self-consistent spin-wave theories (SSWT) of two-dimens ional Heisenberg ferro- and antiferromagnets with a weak interlayer couplin g and/or magnetic anisotropy, that are based on the nonlinear. Dyson-Maleev , Schwinger, and combined boson-pseudofermion representations, are analyzed . Analytical results for the temperature dependences of (sublattice) magnet ization and the short-range order parameter, and the critical points are ob tained. The influence of external magnetic field is considered. Fluctuation corrections to SSWT are calculated within a random-phase approximation whi ch takes into account correctly leading and next-leading logarithmic singul arities. These corrections are demonstrated to improve radically the agreem ent with experimental data on layered perovskites and other systems. Thus a n account of these fluctuations provides a quantitative theory of layered m agnets.