LOCAL ENVIRONMENT AND VIBRATIONAL CHARACTERISTICS OF SN-119(II) MOSSBAUER PROBE ATOMS LOCATED ON THE SURFACE OF CR2O3 MICROCRYSTALS

Two different sites have been evidenced for Sn(II) dopant atoms locate d at the surface of the Cr2O3 substrate. Their inequivalence appears t o be essentially due to the number of neighboring CI (III) cations whi ch are responsible for the magnetic hyperfine fields H transferred at the Sn-119 nuclei. While a large difference is observed in the saturat ion values of H, the isomer shift and quadrupole splitting-which are p redominantly 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 Sn-119 nuclei is found, in both cases, to be negati ve and oriented at the same angle with respect to the c-axis of the Cr 2O3 lattice. The magnetic ordering temperature detected by the surface -located Sn-119(II) atoms appears to be in good agreement with that pr eviously determined from antiferromagnetic resonance experiments for u ndoped Cr2O3. 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 perpe ndicular to this direction.