Unconventional magnetic behavior of iron-oxide nanoparticles in polymeric matrices

We report the results of magnetization and Fe-57 Mossbauer spectroscopy measurements performed in the temperature range 5-300 K on composites containing iron-oxide nanoparticles encased in polystyrene type resins. After carrying out a suitable field treatment in order to decouple the particles from the matrix, a fraction of the particles freely rotate in response to an applied magnetic field. (C) 2001 American Institute of Physics.