Enhanced tunneling magnetoresistance and high-spin polarization at room temperature in a polystyrene-coatedFe3O4granular system

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Polystyrene-coated ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ nanoparticles through surface engineering exhibit an intergranular tunneling magnetoresistance (MR) ratio of 22.8% at room temperature and a maximum MR of 40.9% at $110\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The drastic enhancement of the MR ratio clearly suggests that there is high degree of spin polarization even at room temperature for half metallic ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$. The estimated spin polarization $P$ is about 54% and 83% at room temperature and $110\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, respectively.