Local environment and vibrational characteristics of 119Sn(II) Mössbauer probe atoms located on the surface of Cr 2O 3 microcrystals

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Two different sites have been evidenced for SN(II) dopant atoms located at the surface of the Cr 2O 3 substrate. Their inequivalence appears to be essentially due to the number of neighboring Cr(III) cations which are responsible for the magnetic hyperfine fields H transferred at the 119Sn nuclei. While a large difference is observed in the saturation values of H, the isomer shift and quadrupole splitting—which are predominantly determined by tin-oxygen bonding—differ for the two sites to a lesser extent. Moreover, the main component V zz of the electric field gradient at 119Sn nuclei is found, in both cases, to be negative and oriented at the same angle with respect to the c-axis of the Cr 2O 3 lattice. The magnetic ordering temperature detected by the surface-located 119Sn(II) atoms appears to be in good agreement with that previously determined from antiferromagnetic resonance experiments for undoped Cr 2O 3. The Goldanskii-Karyagin effect, which is observed for Sn(II) dopant atoms in the paramagnetic region, indicates that the mean square vibration amplitudes are smaller along the V zz axis than perpendicular to this direction.