CSU Physics Colloquium

Enhanced tunneling magnetroresistance & high spin polarization in polystyrene coated Fe3O4 granular systems

Dr. Jinke Tang

University of Wyoming

Mon,  11/16

Calculations predict that magnetite is a half-metal, which is a conductor for one spin direction and semiconductor/insulator for the other spin direction. In reality, low spin polarization and low magnetoresistance have been observed instead. The speculated causes for the experimental results include deviation from Fe3O4 stoichiometry on the surfaces,, surface reconstruction, the presence of magnons (surface and bulk), surface magnetic states being different from the bulk, and the quality of barrier. We have investigated polystyrene-coated Fe3O4 nanoparticles. Through surface engineering, these nanoparticles exhibit an intergranular tunneling magnetoresistance of 22.8% at room temperature and a maximum MR of 40.9% at 110 K. The large enhancement of the MR suggests that there is high degree of spin polarization even at room temperature for half metallic Fe3O4. The estimated spin polarization P is about 54% and 83% at room temperature and 110 K, respectively.