You might find your answer here..............Kuznetsov O. A.; Sorokina O. N.; Leontiev V. G.; Shlyakhtin O. A.; Kovarski A. L.; Kuznetsov A. A. (2007) ESR study of thermal demagnetization processes in ferromagnetic nanoparticles with Curie temperatures between 40 and 60 {ring operator} C. J. Magn. Magn. Mater. 311, 204–207.