Free rotation of magnetic nanoparticles in a solid matrix

Magnetic data for a composite material consisting of nanocrystalline gamma -Fe2O3 dispersed in an alginate methanol matrix indicate the presence of ro tationally free magnetic particles. The decoupling of the particles from th e matrix was achieved by subjecting the sample to a magnetic field applied in alternating directions. Before field treatment, a magnetic blocking proc ess is observed at low temperature, which is characteristic of nanoscale ma gnetic materials in the presence of barriers for the magnetic moment of the particles. After the field treatment, no magnetic hysteresis is observed a nd the magnetization follows a Curie-Weiss law. This behavior can only be i nterpreted as due to magnetic moments that follow the external magnetic fie ld without delay, implying, therefore, the existence of free particles.