Sergey P. Naumov

Impact that addition of 1%Ga to the Fe-15%Ni alloy exerts on the phase transformations and structure constituents has been studied by x-ray diffraction, scanning electron microscopy, Mössbauer spectroscopy, and magnetic susceptibility measurements. The results show that alloying with Ga changes the course and temperatures of forward and reverse martensite transformations and the very morphology formed after annealing in the two-phase region. In the Fe ₈₅ Ni ₁₅ alloy, polygonal Fe–Ni FCC precipitates enriched in Ni are observed at the boundaries of recrystallized BCC grains inhomogeneous in composition. At the same time, the microstructure of the Fe ₈₄ Ni ₁₅ Ga ₁ alloy consisting of martensite plates coherently connected with lath precipitates formed along the boundaries, with both structure constituents being homogeneous with respect to Ni content, is observed for the first time. Moreover, some indications are obtained to the ferromagnetic state of these lath precipitates.

In this paper, the electron and magnetic state of iron placed either on the surface or in the core of TiO₂ nanoparticles were investigated using magnetometric methods, electron paramagnetic resonance (EPR) and Mössbauer spectroscopy. It was demonstrated that the EPR spectra of TiO₂ samples with iron atoms localized both on the surface and in the core of specific features depending on the composition and size of the nanoparticles. Theoretical calculations using the density functional theory (DFT) method demonstrated that the localization of Fe atoms on the surface is characterized by a considerably larger set of atomic configurations as compared to that in the core of TiO₂ nanoparticles. Mössbauer spectra of the samples doped with Fe atoms both on the surface and in the core can be described quite satisfactorily using two and three doublets with different quadrupole splitting, respectively. This probably demonstrates that the Fe atoms on particle surface and in the bulk are in different unlike local surroundings. All iron ions, both on the surface and in the core, were found to be in the Fe³⁺ high-spin state.

To specify what triggers the magnetostructural transition in CeFe₂ doped with silicon, the temperature dependences of the magnetization, as well as the initial magnetic susceptibility and field dependences of the magnetization of the rare-earth intermetallic compounds Ce(Fe_{1 – x}Si_x)₂ with the silicon content x ≤ 0.05, were measured. The transition temperature to the magnetically ordered state and the average magnetic moment at Fe atoms were determined, and the magnetic contribution to the entropy change was estimated. Mössbauer spectra of Ce(Fe_{1 – x}Si_x)₂ (x ≤ 0.05) in the paramagnetic state were measured with a discretization of velocity scale of 512 channels, processing of which served to confirm the earlier suggested local ordering of Si atoms in the Fe sublattice.

The ¹⁶ O/ ¹⁸ O oxygen exchange kinetics between the gas phase and the oriented single crystal and polycrystalline specimen has been studied; the rates of individual stages of oxygen exchange have been calculated and discussed.

New nonstoichiometric compounds CeFe₂Mn_x with a structure of the cubic Laves phase have been synthesized. The concentration range of Mn solubility has been determined. The structure and elemental composition were studied by means of X-ray powder diffraction and energy-dispersive X-ray spectroscopy. Temperature dependences of magnetization were measured. To determine Curie temperatures, magnetic susceptibility measurements were performed. The results obtained for the samples of different compositions of nonstoichiometric and quasi-binary compounds are analyzed taking into account specific features of electronic structure of Ce atoms.