Enhanced low field magnetoresistance of Fe3O4 nano-sphere compact

TL;DR

This study reports a significant low field magnetoresistance in Fe3O4 nanosphere compact at room temperature, driven by spin-dependent scattering at grain boundaries, with properties varying across temperatures.

Contribution

It demonstrates unusually large LFMR at 300 K in Fe3O4 nanospheres and analyzes its temperature-dependent behavior related to grain boundary effects.

Findings

LFMR of ~10% observed at 300 K

LFMR does not depend on Verwey transition near 115 K

LFMR saturates quickly with magnetization at 300 K

Abstract

Unusually large low field magetoresistance (LFMR), ~ 10 %, at 300 K has been observed with the sample of mono-dispersed Fe3O4 magnetite nanospheres, ~ 200 nm, compactly cold-pressed and sintered at 800 C. A detailed analysis on the transport and magnetic measurements indicates that the electron conduction is dominated by the spin-dependent scattering or tunneling at the grain boundaries. At low temperature, 140 K and 100 K near the Verwey transition, ~ 115 K, the LFMR (below 2 kOe) does not show any sign of dependence on the transition, and does not follow the variation of magnetization to reach the saturation region either. On the other hand, at 300 K, the MR saturates fast with the magnetization below 2 kOe. This temperature dependent property in LFMR is very likely attributed to the scattering or tunneling of the conduction electron passing through the grain boundary layer with spin disordered state.