Magnetic Properties Of Ferromagnetic And Ferrimagnetic Bilayer Systems In Variational Cumulant Expansion

The magnetic properties of the bilayer system, consisting of spin-1/2 and spin-3/2 ferromagnetic monolayers coupled ferromagnetically or ferrimagnetically, are investigated by using variational cumulant expansion. The temperature dependences of magnetizations are calculated up to the second order in order to clarify the influences of inter- and intra-monolayer interaction, and crystal-field interaction of spin-3/2 monolayer. A number of characteristic behaviors for their variations are obtained for these interactions. In the ferromagnetic bilayer system, the stepwise behavior of magnetic curve can be observed , but this behavior disappears when inter-interaction become large, and magnetic curves can low in low temperature regions and rise in high temperature regions. In the ferrimagnetic bilayer system, the magnetic curves can exhibit N-type and P-type behaviors. These indicate that the ferromagnetically and ferrimagnetically coupled multiplayer system may be a very interesting system.