[en] We present an nuclear magnetic resonance study of hyperfine fields at ⁵⁷ Fe nuclei in polycrystalline yttrium iron garnet. We measured spectra of ⁵⁷ Fe nuclei situated in tetrahedral and octahedral sites in magnetic domains as well as in domain walls at several temperatures within the range of 4.2-344 K. Comparing the simulated lineshapes to the experimental ones we found that the main contribution to the observed spectra from walls originated from nuclei in 70.5 deg Bloch walls (Authors)

[en] Temperature dependence of nuclear magnetic resonance (NMR) spectra of ⁴⁷Ti and ⁴⁹Ti in polycrystalline ilmenite FeTiO₃ was measured in the range from 5 to 300 K under an external magnetic field of 9.401 T. NMR spectra collected between 300 and 77 K exhibit a resolved quadrupole splitting. The electric field gradient (EFG) tensor was evaluated for Ti nuclei and the ratio of ⁴⁷Ti and ⁴⁹Ti nuclear quadrupole moments was refined during the fitting procedure. Below 77 K, the fine structure of quadrupole splitting disappears due to the enormous increase of anisotropy. As a counterpart, ab initio calculations were performed using full potential augmented plane waves + local orbitals. The calculated EFG tensors for Ti and Fe were compared to the experimental ones evaluated from NMR and the Moessbauer spectroscopy experiments.

[en] Temperature dependences of the hyperfine magnetic fields at ⁵⁷Fe nuclei in five magnetic sublattices of BaFe₁₂O₁₉ hexagonal ferrite were analyzed to obtain parameters characterizing the local exchange interactions. We report theoretical analysis of the temperature dependences of magnetization carried out in the framework of various cluster models based on mean field approaches including the Bethe-Peierls-Weiss approximation. Exchange integrals were extracted from the experimental data reported earlier by G. Albanese et. al. (1974) and P.Novak et al. (1989) (Authors)

[en] We prepared multiferroic Y-type hexaferrite Ba_0.5Sr_1.5Zn₂Fe₁₂O₂₂ ceramics and compared their magnetic and dielectric properties with single crystal. Magnetic susceptibility and microwave resonance measurement revealed magnetic phase transition at T_C=312 K, similar as in single crystal. Ferroelectric (FE) phase can be induced by external magnetic field in all investigated samples and the phase diagram in ceramics qualitatively resembles that of the single crystal. The range of magnetic fields, where the FE phase is induced, broadens after annealing of single crystal. Ceramics quenched after sintering exhibit several orders of magnitude lower conductivity than the single crystal. Heavily damped magnetic resonance was discovered in terahertz spectra at 10 K and its frequency softens below 5 GHz near T_C. Number and symmetry of observed infrared (IR) and Raman active phonons correspond to paraelectric phase with D_3d⁵ hexagonal structure. No evidence for a structural phase transition was found in the IR and Raman spectra on cooling (in zero magnetic field) or in the room-temperature IR spectra with external static magnetic field up to 0.3 T.

[en] Magnetite single crystals with Al, Ga and Ti substitutions were measured by means of ⁵⁷Fe nuclear magnetic resonance (NMR) technique. Satellite structure of NMR spectra well above the Verwey temperature was detected and analyzed to obtain information on the distribution of substituting cations on iron sublattices. It was confirmed that Al and Ti enter iron octahedral B-sites. Ga strongly prefers tetrahedral A-sites, nevertheless a low presence of Ga cations in B-sites was detected