Nickel oxide nanoparticles doped with tin NiO:0.3 at. % Sn 4 + with the average X-ray diffraction diameter d X R D = 38 nm have been studied by Mossbauer spectroscopy. The 1 1 9 Sn spectra show a hitherto unobserved system of hyperfine structure lines, which is characterized at 5 K by the isomer shift δ = 0.29 ′ 0.02 mm/s and the magnetic field H = 229 ′ 1 kOe. This spectral component is assigned to the Sn 4 + ions that occupy substitution positions with the intact local cationic environment. Comparison of this H value with those obtained for isostructural antiferromagnets MnO and CoO shows that the spin polarization of 1 1 9 Sn 4 + in matrices of this type is mainly determined by the half-filled eg orbitals of a 3d cation involved in 180° indirect exchange. In addition to this component, the spectra point to the presence of 1 1 9 Sn 4 + ions with a disturbed magnetically active environment. Although the contribution of these ions is dominant, identification of the corresponding positions is impossible due to the nonuniform distribution of tin over nanoparticles of different sizes, which transform, as shown by 1 1 9 Sn spectra, into the superparamagnetic state at 350 K.

The magnetic fields H at the Sn-119(IV) nuclei located in the COO structure in positions of two types-H-1 = 193 kOe (78 K) for the positions with a complete cationic environment and H-2 = 155 kOe (78 K) for the positions containing a charge-compensating vacancy V-Co(II) instead of the neighboring cobalt atom along a unit cell edge-were determined. The H, value is comparable with that observed for the Sn-119(IV) ions in the isostructural antiferromagnet MnO, which indicates that the spin polarization of tin in both oxides is mainly caused by the e 9 orbitals of 3d cations involved in 180degrees indirect exchange. Comparison of the H values and isomer shifts for Sn-119(IV) in CoO and MnO with those in the isostructural antiferromagnetic sulfide MnS shows that an enhancement in covalence contributes to delocalization of 3d electrons; however, their spin density in the 5s orbital of Sn-119(IV) becomes more "diluted" with an increased density of electrons with paired spins.

A sample of CoO with a nonequilibrium distribution of Sn(IV) ions over structural positions with nonequivalent cationic environments was studied by Mossbauer spectroscopy. Analysis of Sn-119 hyperfine coupling made it possible to calculate the partial contributions of 180degrees indirect exchange involving the e(g) orbitals (h(ie) approximate to 30 kOe) and direct exchange involving the half-tilled t(2g) orbitals of neighboring Co(II) cations (h(de) approximate to 10 kOe) to the magnetic field H at the tin nuclei.

Hyperfine interactions of (57)Fe and probe (119)Sn nuclei in dicalcium ferrite with a brownmillerite-type structure were studied by Mossbauer spectroscopy. Parameters of the EFG tensor for the Fe(3+) cations located in octahedral and tetrahedral oxygen environments were calculated in terms of the "ionic" model including monopole and dipole contributions. The calculated values are consistent with the experimental data of (57)Fe spectra. The (119)Sn spectra recorded below the magnetic ordering temperature (T < T(N)) support the assumption that the Sn(4+) cations are located in the octahedral sublattice of ferrite. Analysis of the asymmetry of the (119)Sn quadrupole doublet components at T > T(N) showed that the mean-square amplitudes of Sn(4+) thermal vibrations along the EFG direction are greater than those in the perpendicular direction. The temperature behavior of the (119)Sn spectra is described in terms of the one-parameter Debye model.