MAGNETIC PHASE-TRANSITIONS WITH FINAL ORDERING - PECULIARITIES IN THE CRITICAL-BEHAVIOR

Magnetic crystals containing two subsystems of different types of magnetic ions are considered. It is assumed that the subsystem of the first type of the ions is already ordered at relatively high temperature, while the ordering temperature of the second subsystem is much smaller. We present an analysis, which is performed by use of the Landau-Ginzburg method, of the critical behavior of such double magnetic systems in the vicinity of the ordering temperature of the second subsystem. This temperature is referred to as the temperature of the final ordering. We demonstrate the suppression of the anomalous fluctuations near the point of the phase transition of the final ordering. The peculiarities of the critical behavior in the vicinity of the points of phase transitions of the final ordering in low-dimensional magnets are also discussed.