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

Abstract

We report a facile method to enhance the magnetoresistance (MR) of magnetite (Fe3O4) nanoparticles assemblies using encapsulating with polyvinyl acetate (PVAc). Fe3O4 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 Fd3¯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 Fe3O4 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.