MAGNETIC-PROPERTIES OF NEW LAYERED HEISENBERG ANTIFERROMAGNETS

The magnetic properties of layered Heisenberg antiferromagnets with antiferromagnetic interaction between spins within a layer and ferromagnetic interaction between layers are studied by using a spin-wave theory and double time-temperature spin Green's function theory. At low temperatures a characteristic temperature is defined reflecting the layered features of the system and the low-temperature region is divided into two new ones, giving asymptotic expressions of sublattice magnetization and parallel susceptibility in different temperature regions, including the low-temperature.region, the vicinity of the Neel temperature, and the high-temperature region. Also given is the Neel temperature in an asymptotic form when the interlayer coupling is weak. It is shown that the characteristics of dimensional cross-over for physical quantities exists at low temperatures. The interlayer coupling is essential to keep long-range ordering and the properties of this kind of antiferromagnets are very similar to those of normal antiferromagnets.