Magnetic properties, internal energy and specific heat of a three-layer Heisenberg system with six sublattices

The magnetic properties of a three-layer Heisenberg model with spins at six sublattices are investigated by using retarded Green's function method and spin-wave theory. The spin-wave spectra of the system and the energy gap are calculated numerically, which are related to the magnetic symmetrical structure of the model. The quantum fluctuation at zero temperature, magnetization, internal energy and specific heat at low temperature are compared under different sets of intra- and interplane coupling interactions. The results show that the ferrimagnetic coupling plays an important role in various physical properties of the system.