Correlation functions of the magnetization in thin films

We calculate the correlation functions of uniform magnetization in thin ferromagnetic films for small deviations from equilibrium using a functional formalism. To take account of dissipation and fluctuations consistently,the magnetization is coupled linearly to a bosonic heat bath. The correlation functions of the magnetization strongly depend on the density of states of the bath. Depending on what density of states we choose, we show how the recent results of Smith [J. Appl. Phys. 90, 5768 (2001)] and Safonov and Bertram [Phys. Rev. B 65, 172417 (2002)] obtained by macroscopic methods can be understood in light of the microscopic treatment presented here.