SPECIFIC-HEAT OF A HEISENBERG-SYSTEM WITH FINITE-SIZE

Based upon the spin wave theory, the influence of the size of a three-dimensional Heisenberg system on its thermodynamic properties was studied. It is found that the specific heat increases due to the finite size and free surface of the system. For a magnetic film with finite thickness, the interaction of spin waves was also discussed. There exist three additional scattering processes, namely, the scattering between spin waves with wave-vectors parallel to the surface of the film (two-dimensional spin wave), the scattering between two and three-dimensional waves, and the scattering between those waves with the same component in the direction along the thickness of the film. As a result, the T-4 term, arising from the coupling of spin waves, in the expression of the specific heat of the system, splits into three parts proportional to T-5/2, T-7/2 and T-4, respectively. Here T is the temperature.