Giant tunneling magnetoresistance in polycrystalline nanostructured ZnxFe3-xO4-α-Fe2O3

Giant tunneling magnetoresistance effect (TMR) as large as 1280% at 4.2 K and 158% at 300 K was observed in Zn_0.41Fe_2.59O₄-α-Fe₂O₃ polycrystalline sample. The Zn_0.41Fe_2.59O₄ grains are separated by insulating α-Fe₂O₃ thin layer boundaries, The pattern of nanostructure has been verified by transmission electron microscopy and a high-resolution electron microscope, and the thickness of α-Fe₂O₃ boundary is about 6-7 nm. The huge TMR is attributed to the high spin-polarization of Zn_0.41Fe_2.59O₄ grains and insulating antiferromagnetic α-Fe₂O₃ thin layer. The conductivity is found to depend exponentially on reciprocal temperature, which means the electronic transfer is dominated by thermally activated tunneling from grain to grain. The Zn_xFe_3-xO₄ ferrite is a new type half-metallic material and has a huge TMR at room temperature.