Magnetic phase diagrams and magnetization curves of ferrimagnets with one unstable magnetic subsystem

Magnetic phase diagrams and schematic magnetization curves are given for a ferrimagnet, one magnetic subsystem of which undergoes a metamagnetic transition from a weekly to a strongly magnetic state. In the simple model of the molecular field theory it is shown that in such systems magnetic phase transitions of different nature are possible, and the phase diagrams are of various topology depending on the relation of the system parameters. The magnetization curves for the substituted intermetallic compounds Y(1-t)R(t)(Co1-xAlx)(2) (R is a heavy rare earth element) are calculated for the actual parameters of the system.