Fluctuation-dissipation considerations and damping models for   ferromagnetic materials
  The role of fluctuation-dissipation relations (theorems) for the magnetization dynamics with Landau-Lifshitz-Gilbert and Bloch-Bloembergen damping terms are discussed. We demonstrate that the use of the Callen-Welton fluctuation-dissipation theorem that was proven for Hamiltonian systems can give an inconsistent result for magnetic systems with dissipation. 
Vladimir L. Safonov and H. Neal Bertram