Hyperfine interactions of iron implanted into aluminium

Stable⁵⁷Fe implanted into Al at energies of 20 to 70 keV and doses of 10¹⁴ to 2·10¹⁷ ions/cm² was studied with conversion electron Mössbauer spectroscopy at room and liquid nitrogen temperatures. Spectra composed of a single line and a doublet were observed. Similarly as in the splat-quenched FeAl alloys iron monomers and iron associations, mostly dimers, are observed. The isomer shifts of both components differ considerably and do not change with iron concentration. The splitting of the doublet increases with iron concentration, the increase being reproduced by computer simulations of electric field gradients in lattices with a random distribution of charge defects. The observed probability of formation of iron associates is higher than in random systems, especially at high iron doses.