A.R. Kilmametov

Influence of interface on structure and magnetic properties of Fe50B50 nanoglass

In contrast to rapidly quenched metallic glasses, nanoglasses consist of two components, namely amorphous nanograins and interfacial regions with distinctively different properties. Various physical methods have been employed to obtain information on the atomistic and magnetic properties of such materials. For the case of a Fe50B50 nanoglass, using high-energy X-ray diffraction, it was found that the short-range order of the nanograins is similar to that of a crystalline FeB alloy. Magnetic Compton scattering shows that the total magnetic moment is the sum of the magnetic moment of the nanograins and the weak magnetic moment of the interfacial regions (μInterface = +0.08 μB). The measured moment of boron agrees (μBoron = −0.08 μB) with linear Muffin-Tin calculations. From the results of Mossbauer and magnetic Compton scattering, it can be concluded that the boron atoms segregate in the interfacial regions, resulting in a reduced boron concentration in the nanograins.

Transformation of Hume-Rothery phases under the action of high pressure torsion

It has been revealed experimentally that high-pressure torsion induces phase transformations of certain Hume-Rothery phases (electron compounds) to others. High-pressure torsion induces the ξ → δ + ɛ reaction in copper-tin alloys with the appearance of the δ + ɛ phase mixture as after long-term annealing in the temperature range Teff = 350–589°C. The mass transfer rate driven by high-pressure torsion is 14–18 orders of magnitude higher than the rate of conventional thermal diffusion at the processing temperature THPT. This phenomenon can be explained by an increased concentration of defects (in particular, vacancies) in the steady state under high-pressure torsion, which is equivalent to an increase in the temperature.

Controlling spin polarized band-structure by variation of vacancy intensity in nanostructures

In this study, the magnetic properties of FeAl alloys with different grain sizes produced by high-pressure torsion were probed by means of magnetic Compton scattering. The measurements were performed at 300 and 10 K. Magnetic Compton profiles of nanocrystalline (35 nm) and ultrafine-grained (160 nm) FeAl alloys were analyzed in terms of the integral area, the width, and the distinctive dip intensity at low momenta. The changes in total magnetic moment and the strength of spin-polarization of itinerant electrons are assumed to be caused by vacancies induced during the preparation of the samples. Despite local disordering due to interfacial regions and deviations in perfect stoichiometry for B2 structure, the effect of vacancies is considered as the major magnetic state contributor.