Specific effect of hydrogen implantation in yttrium iron garnet and annealing behavior studied by conversion-electron Mössbauer spectroscopy

Conversion-electron Mössbauer-spectroscopy technique applied to ${}_{}{}^{57}{}_{}{}^{}$Fe-enriched yttrium iron garnet has allowed us to obtain good resolution of the spectra characteristic of the different iron sites. Its association with infrared spectroscopy has permitted us to show clearly the specific chemical effect of hydrogen implantation in comparison with a pure damage effect from a shallow neon implantation. Ne and H implantations affect preferentially the tetrahedral sites by changing the magnitude and directions of magnetizations. Moreover, for H implantation the presence of a new ‘‘$d_{\mathrm{H}}$’’ magnetic site among the tetrahedral sites has been clearly correlated with the formation of O–H bonds. However, this effect concerns only about 15% of the implanted hydrogen; the remaining part responsible for the reduction of iron gives rise to the observation of characteristic effects on the Mössbauer spectra (line broadenings, hyperfine-field decreases, etc.). From the thermal-annealing behavior of H-implanted crystals two stages can be distinguished: Up to 350 °C, when hydrogen is still present in the implanted volume, different evolutions of the Mössbauer spectra compared to those of a Ne-implanted crystal are observed; above 350 °C, when hydrogen is completely diffused out of the garnet, the evolutions are similar except for the magnetization directions of $d^{\mathcal{’}}$ sites and the persistence of the $d_{\mathrm{H}}$ component up to 850 °C.