Enhancement of room-temperature magnetoresistance in polyvinyl acetate encapsulated Fe3O4 nanoparticles

We report a facile method to enhance the magnetoresistance (MR) of magnetite (Fe ₃O ₄) nanoparticles assemblies using encapsulating with polyvinyl acetate (PVAc). Fe ₃O ₄ nanoparticles of various size distributions have been synthesized by a chemical co-precipitation method. X-ray diffraction study revealed the formation of cubic inverse spinel structure with Fd 3 ¯ m space group. Morphology and the particle size distributions were studied using FESEM and TEM. The films of smaller sized nanoparticles show higher resistivity, and a significant drop in resistivity was observed after the PVAc encapsulation over the film. Negative MR of 1.7–2.13% was observed with the decrease of mean particle size from ∼ 50 nm to 21 nm at room temperature under 0.5 T, which was increased to 4 – 8.4 % after the PVAc encapsulation. The large low field magnetoresistance is mainly attributed to the tunnelling of high spin polarized electrons in Fe ₃O ₄ grains through the spin disordered grain boundaries. The encapsulation of PVAc over the nanoparticles film reassembles the nanoparticles and reduce the interparticle distances by producing a compressive stress, which reduces the tunnelling barrier for the interparticle charge transport and improves the magnetoresistance.