Structure and magnetism of granular Fe-Al2O3

The structural and magnetic properties of granular Fe-Al2O3 nanocomposite o btained starting from sol-gel processing are presented. Samples with nomina l Fe content ranging from 20% to 62% in volume were prepared. The conversio n of Fe oxides into metallic Fe was obtained by calcination at 800 degreesC followed by reduction at 600 degreesC for 2 h in H-2 atmosphere. After red uction, our results indicated up to 78% alpha -Fe, preserving the mean diam eter of the metallic nanoparticles between 50 and 80 nm, similar to 16% Fe oxides and similar to 7% interstitial Fe2+ and substitutional Fe3+ cations in the Al2O3 lattice. Vibrating sample magnetometry at 300 K resulted in co ercivity between 400 and 630 Oe and saturation magnetization between 40 and 134 emu/g. From transport measurements, the highest magnetoresistance, clo se to 2% at room temperature, was observed for samples with 25% alpha -Fe a nd 51 vol% total Fe. (C) 2001 Elsevier Science B.V. All rights reserved.