Study On The Thermodynamic Properties Of Quantum Heisenberg Ferromagnetic Films

With the rapid development of semiconductor and the technique of plating, the dimensions of electronic device have been extended to the scale of micro/nano. When the thickness of films is diminished to extra thin films,all its structure,micro-structureNthermodynamic and magnetic properties can differ drastically from those of the bulk ones. As the quantum effect, the limitations of material and the giant surface and interface effect, the thermodynamic properties of the micro-measure material will produce a distinct dimensional effect, thus the thermodynamic properties of the electronic device cause the people' s concern. In modern technology, films, especially the extra thin films have occupied an important place in the micro machinery and microelectronics device, so the analysis on the thermodynamic properties of films is significant to study and develop the device.The quantum Heisenberg model is suitable for magnetic insulating material, that is widely and successfully used in the spin-wave theory of ferromagnetic and anti-ferromagnetic material. In termsof theory, people have developed many approximate methods: such as mean-field theory (MFT), renormalization group, Monte Carlo (MC) and effective-niolecule-field treatment et al. Usually the MFT or amendatary MFT is adopted, and the rational spin-statistical models are used to investigate the properties of magnetic metal films. Unfortunately, the higher-order corrections to mean-field analysis turn out to be extremely difficult to handle in various effective treatment. Therefore, it is worth while to explore other simple and effective theoretical approaches to calculate the magnetic films, where corrections can be treated systematically. In recent years, domestic and foreign theoretical scholars have found that the variational cumulant expansion (VCE) shows a great advantages in researching the critical points of the samdwich models. And it has been proved to be a very effective method for the studying of lattice gauge field models.The thermodynamic properties of the magnetic thin films based on the quantum Heisenberg model are studied. It is the VCE that is adopted to study on the thermodynamic properties of different lattice planes for spin-1/2 Heisenberg magnetic films with simple cubic lattices by using a graphic technique. The critical temperature, internal energy and specific heat are calculated to the third order. We analyse the dependence of critic temperature of different crystal face on the atomic layers, and compare their results. At the same time, the influence of atomic layers in the films to the variations of internal energy and specific heat of different crystallographic planes is compared and discussed.