Large room-temperature spin-dependent tunneling magnetoresistance in a Fe3O4-polymer composite system

Powders of polymer and -Fe2O3 nanoparticles were pressed into pellets. The samples were annealed at 250 °C in pure hydrogen flow. X-ray diffraction spectra indicate that there is a complete phase transformation from -Fe2O3 to Fe3O4. Giant negative magnetoresistance MR was observed at room temperature and the MR ratio is over 14% in an applied field of 5.5 T. The maximum MR ratio is higher than 22% at 130 K. The drastic enhancement of the MR ratio is attributed to the fact that the polymer is an excellent barrier material and, more importantly, prevents the oxidation of the surface of Fe3O4. Our results clearly suggest that there is a high degree of spin polarization at room temperature for half-metallic Fe3O4.