Mössbauer characterization of tin dopant ions in the antiferromagnetic ilmenite MnTiO3

Mössbauer parameters of ¹¹⁹Sn diamagnetic dopant cations in an antiferromagnetic compound having the ilmenite structure are for the first time reported. The spectra reveal a well resolved hyperfine splitting pattern of combined magnetic and quadrupole interactions (at 5 K, δ=0.19 mm/s, H₁=52.5 kOe, eV_ZZQ_3/2=−0.80 mm/s, θ≈0°). This spectral component whose contribution (A₁=82%) represents more than four fifths of the total amount of the dopant (Sn/(Mn+Ti)=1/200) is assigned to Sn(IV) ions located in the bulk of MnTiO₃, on the Mn(II) site, and with a Mn(II) vacancy in their nearest surrounding. Two spectral components with minor contributions are also observed: one of them (H₂≈25 kOe, A₂=8%) can be assigned to Sn(IV) ions, in the MnTiO₃ lattice as well, on a site where they exhibit a weaker spin polarization (this site could be the Ti(IV) one) and the other (H₃=0 kOe, A₃=10%) to SnO₂ or/and Ti_1−xSn_xO₂ clusters. The Néel temperature of MnTiO₃ probed by the ¹¹⁹Sn dopant (T_N=69±2 K) agrees well with the values previously provided by ESR and antiferromagnetic resonance measurements. Variation of H₁ with temperature follows close the Brillouin function for S=5/2. No perturbation appears in the Mössbauer spectra around T=90 K where a broad peak, characteristic of 2D magnetic interactions, is observed on the static magnetic susceptibility curve.