Figure 1

(a) TEM image for the PS-coated ${\mathrm{Fe}}_3{\mathrm{O}}_4$ sample, indicating that spherical ${\mathrm{Fe}}_3{\mathrm{O}}_4$ nanoparticles are embedded in polymer matrix. (b) High-resolution TEM image showing that the ${\mathrm{Fe}}_3{\mathrm{O}}_4$ particles are separated by a thin polymer layer of a few nanometers, forming a tunnel barrier.Reuse & Permissions

Figure 2

MR ratio in an applied field of $14\mathrm{T}$ at 280 and $110\mathrm{K}$ for (a) PC-coated ${\mathrm{Fe}}_3{\mathrm{O}}_4$ and (b) PS-coated ${\mathrm{Fe}}_3{\mathrm{O}}_4$. The weight ratio of ${\mathrm{Fe}}_3{\mathrm{O}}_4$ to polymers is 1:1 for both. The MR ratio of PMMA-coated ${\mathrm{Fe}}_3{\mathrm{O}}_4$ is similar to that of PC-coated samples. (Left insets) resistance as a function of temperature: $\log R$ versus $T^{-1∕2}$ curves exhibit linear relation; (Right insets) I-V curves at room temperature which have nonlinear behavior. These are consistent with the transport mechanism of intergranular tunneling. (c) Magnetic hystereses and (d) butterfly-shaped MR hyestereses in low fields for PS-coated ${\mathrm{Fe}}_3{\mathrm{O}}_4$.Reuse & Permissions

Figure 3

(a) Temperature dependence of MR ratio in an applied field of $14\mathrm{T}$ for a PS-coated sample. (b) ZFC-FC curves with an applied field $H=200\mathrm{Oe}$, which shows sharp Vervey transition in the range of $110–120\mathrm{K}$ in our samples.Reuse & Permissions

Figure 4

$\mathrm{Al}\mathrm{K}\alpha$-exited Fe $2p$ core-level photo emission spectra for (I) pure ${\mathrm{Fe}}_3{\mathrm{O}}_4$ powder sample, (II) PC-coated ${\mathrm{Fe}}_3{\mathrm{O}}_4$, (III) PMMA-coated ${\mathrm{Fe}}_3{\mathrm{O}}_4$, and (IV) PS-coated ${\mathrm{Fe}}_3{\mathrm{O}}_4$. The arrow indicates the characteristic shake-up satellite associated with $\mathrm{Fe}(3+)$ ion photoemission at a binding energy of $\sim 719\mathrm{eV}$.Reuse & Permissions