Spin Wave Theory In Four Sublattices System

Layered magnetic systems have been a subject of growing interest in recent years. In particular, the research has been focused on systems such as superlattices and multilayers. In this paper, the two layers system consists of four sublattices. It is convenient to divide to the system into four sublattices A, B, C, and D. Among which sublattices A and B are for the first layer with the spin values of S_a and S_b, respectively, C and B are for the second layer with the spin values of S_a and S_d , respectively. The Hamiltonian is as follows: (?) . The sublattice magnetizations, internal energy and specific heat have been obtained by applying spin-wave theory and Green function method. The numerical results have been given by numerical calculation.In order to discuss the system conveniently, the paper is divided into two parts. In section two, ferromagnetic-ferrimagnetic bilayer is discussed. For the special case, the magnetic properties of ferromagnetic-antiferromagnetic bilayer system and superlattice have been compared with. In section three, physical properties of ferromagnetic-ferromagnetic double layers are studied.If the spin of sublattice A, B and D are upwards while that of sublattice C is downwards, the system can be treated as ferromagnetic-ferrimagnetic bilayer system. Here, the intralayer exchange J₁ >0 in layer AB, the intralayer exchange J₂ <0 in layer CD, while the interlayer interaction between the two layers can be either ferromagnetic or ferrimagnetic (antiferromagnetic). From the calculation, the curves of the spin-wave spectra, energy gap, sublattice magnetization internal energy and specific heat are plotted.The physical properties of ferromagnetic-ferromagnetic bilayer system are also been studied. In this system, the interlayer interaction between the two layers must be ferrimagnetic. The spin-wave spectra, energy gap, sublattice magnetization internal energy and specific heat have been discussed and plotted.From the calculation, a surprising crossover between the two sublattice magnetizations in each layer at low temperatures occurs in the two systems. We shall discuss these physical properties in the dissertation.