Magnetic Properties Of Double-layer Superlattice

Magnetic material as one kind of functional material is applied more and more widely. With the rapid development of technique of plating, the dimensions of electronic devices are extended to the scale of micro/nano. When films are diminished to extra thin films, all the structure, micro-structure, thermodynamic and magnetic properties are very different from those of the bulk ones. To the basic magnetic theories and applied technologies, it is very significant to research magnetic superlattices. Especially, a method to make artificial materials is obtained from magnetic superlattices theories, and the needful materials can be obtained by changing its ingredients and geometric structure. At the same time, the analysis of magnetic properties of magnetic superlattice in theories gives some significant guidances to the study of new functional materials.Magnetic properties of double-layer ferromagnetic/ferromagnetic superlattices are researched on the basis of Heisenberg model. By linear spin wave approximation, Fourier transformation and Green's function technology, the magnetic properties of ferrimagnetic superlattices and ferromagnetic superlattices are calculated and the effects of the system parameters on their magnetic properties are also analyzed, such as: spin quantum number, interlayer exchange couplings, intralayer exchange couplings, anisotropy constant and external magnetic field. The result shows that system parameters have an important effect on its magnetic properties. Two branches of energy spectra exist in both ferrimagnetic/ ferromagnetic superlattices, and the parameters of the system have important effect on these two branches. S₁(J₁₂) and S₂(J₂₁) have the same effect on the energy gap, and the energy gap increases with increasing the difference between S₁(J₁₂) and S₂(J₂₁). For the ferrimagnetic superlattice, the anisotropy constants D₁ and D₂ have the different effect on the energy gap, and external magnetic field has an effect on it. For the ferromagnetic superlattice, the anisotropy constants D₁ and D₂ have the same effect on the energy gap, and external magnetic field has no effect on it. For double-layer ferromagnetic and ferromagnetic superlattices, the magnetization decreases with increasing temperature, and increases with increasing spin quantum number, intralayer exchange couplings and anisotropy constant. The Internal energy and the specific heat decrease with increasing spin quantum numbers, absolute values of interlayer exchange couplings, intralayer exchange couplings and anisotropy constants. For ferrimagnetic superlattice, the internal energy decreases with increasing external magnetic field, and external magnetic field has no effect on the specific heat. For ferromagnetic superlattice, the internal energy and the specific heat decrease with increasing external magnetic field.