Giant Room-Temperature Magnetoresistance in Polycrystalline ${\mathrm{Zn}}_{0.41}{\mathrm{Fe}}_{2.59}{O}_4$ with $\mathit{\alpha }-{\mathrm{Fe}}_2{O}_3$ Grain Boundaries

A tunneling-type magnetoresistance (MR) as large as $158\%$ is observed at $T=300\mathrm{}\mathrm{K}$ in a polycrystalline ${\mathrm{Zn}}_{0.41}{\mathrm{Fe}}_{2.59}{\mathrm{O}}_4$ sample, in which the ${\mathrm{Zn}}_{0.41}{\mathrm{Fe}}_{2.59}{\mathrm{O}}_4$ grains are separated by insulating $\alpha -{\mathrm{Fe}}_2{\mathrm{O}}_3$ boundaries. The huge room-temperature MR is attributed to the high spin polarization of ${\mathrm{Zn}}_{0.41}{\mathrm{Fe}}_{2.59}{\mathrm{O}}_4$ grains and antiferromagnetic correlations between magnetic domains on both sides of the insulating $\alpha -{\mathrm{Fe}}_2{\mathrm{O}}_3$ boundary. The MR exhibits strong temperature dependence below 100 K and its magnitude is enhanced to reach $1280\%$ at 4.2 K, which may arise from the Coulomb blockade effect.