Renormalization-Group Approach to Spin-Wave Theory of Quantum Heisenberg Ferromagnet

The renormalization-group method is used to analyze the low-temperature behaviour of a two-dimentional, spin-$s$ quantum Heisenberg ferromagnet. A set of recursion equations is derived in an one-loop approximation. The low-temperature asymptotics of the correlation length and the uniform susceptibility are obtained. For small spins ($s= 1/2,1$) the results are essentially different from those in the spin-wave theory.Comment: 9 pages, RevTex 3.0 fil