Giant tunneling magnetoresistance in polycrystalline nanostructured Zn/sub x/Fe/sub 3-x/O/sub 4/-/spl alpha/-Fe/sub 2/O/sub 3/

Giant tunneling magnetoresistance effect (TMR) as large as 1280% at 4.2 K and 158% at 300 K was observed in Zn/sub 0.41/Fe/sub 2.59/O/sub 4/-/spl alpha/-Fe/sub 2/O/sub 3/ polycrystalline sample. The Zn/sub 0.41/Fe/sub 2.59/O/sub 4/ grains are separated by insulating /spl alpha/-Fe/sub 2/O/sub 3/ thin layer boundaries, The pattern of nanostructure has been verified by transmission electron microscopy and a high-resolution electron microscope, and the thickness of /spl alpha/-Fe/sub 2/O/sub 3/ boundary is about 6-7 nm. The huge TMR is attributed to the high spin-polarization of Zn/sub 0.41/Fe/sub 2.59/O/sub 4/ grains and insulating antiferromagnetic /spl alpha/-Fe/sub 2/O/sub 3/ 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/sub x/Fe/sub 3-x/O/sub 4/ ferrite is a new type half-metallic material and has a huge TMR at room temperature.