Effect of interlayer coupling in layered Heisenberg ferromagnets

Abstract

Nonlinear spin-wave theory is used to study the effect of interlayer coupling on the magnetic properties of layered Heisenberg ferromagnets. Magnetization and specific heat are calculated numerically as functions of temperature and the interlayer coupling strength, and compared with the results on the linear spin-wave theory. At low temperatures, according to the extent the interlayer coupling suppresses the two-dimensional spin fluctuations, we define a characteristic temperature and use it to divide the low-temperature region into two new ones. We give the asymptotic expressions of magnetization, internal energy and specific heat in each low-temperature region using asymptotic expansions of Bessel functions instead of the long-wavelength approximation. The features of dimensional crossover for physical quantities are shown, and a comparison between theory and experiments is made.