Enhanced tunneling magnetroresistance and high spin polarization in polystyrene coated Fe$_{3}$O$_{4 }$granular system

Polystyrene coated Fe$_{3}$O$_{4}$ nanoparticles through surface engineering exhibit intergranular tunneling magnetoresistance (MR) ratio of 22.8{\%} at room temperature and a maximum MR of 40.9{\%} at 110 K. The drastic enhancement of the MR ratio clearly suggests that there is high degree of spin polarization even at room temperature for half metallic Fe$_{3}$O$_{4}$. The derived spin polarization $P$ is about 54{\%} and 83{\%} at room temperature and 110 K, respectively. It is possible that a simple tunnel junction made of Fe$_{3}$O$_{4 }$exhibits large MR in a relatively small field. Fe$_{3}$O$_{4}$ may also be used as an effective spin injector. Knowing that our results provided only a lower limit on the spin polarization of Fe$_{3}$O$_{4,}$ it has the potential to play an important role in spintronic devices.