Dilute magnetic properties of Fe doped Al2O3 powders prepared by sol-gel method

Aluminium oxides doped with 1% Fe-57 were prepared by sol-gel method, and annealed for 3 hours at various temperatures between 550 degrees C and 1100 degrees C. Amorphous phases were obtained below 1000 degrees C, and crystalline alpha-Al2O3 was formed at 1100 degrees C. Although Al2O3 itself shows diamagnetism, the light doping of Fe ions into aluminium oxide induced a very weak ferromagnetism, but the ferromagnetism disappeared by longer annealing. Mossbauer spectra were composed of paramagnetic Fe2+ and Fe3+ species for samples heated below 750 degrees C, and of paramagnetic Fe3+ above 850 degrees C, in addition to a magnetic sextet and relaxation peaks of Fe3+. The magnetic and quadrupole interactions of the sextet and the relaxation peaks and the density functional calculations suggest that the lightly doped Fe3+ ions are substituted at Al sites in the Al2O3 lattice.