Unconventional magnetic behavior of iron oxide nanoparticles in polymeric matrices

We report the results of magnetization and 57Fe Mo¨ssbauer 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.