MAGNETIC-PROPERTIES OF LAYERED HEISENBERG FERROMAGNETS

The double-time-temperature spin Green's function method is used to study the magnetic properties of layered ferromagnets with arbitrary spin S, within Tyablikov's decoupling approximation. According to the extent to which interlayer coupling suppresses two-dimensional spin fluctuations, we divide the low-temperature region into two new ones, and give the asymptotic expressions for magnetisation and susceptibility over different temperature regions, including the low-temperature region, the vicinity of the Curie temperature and the high-temperature region. We also give the Curie temperature in an asymptotic form when interlayer coupling is weak.