Vol 118, No 12 (2017)

The Hall resistance and the magnetoresistance in the mixed state of the Nd_{2 − x}Ce_xCuO_{4 + δ} quasi-two-dimensional system near the antiferromagnetic-superconductor (AF-SC) phase transition have been measured at doping levels x = 0.14 and 0.15, and a correlation has been established. This correlation can be analyzed using the following power relationship: ρ_xy(B) ~ [ρ_xx (B)]^β. It was found that index β varied from 0.94 ± 0.03 in the region of AF and SC coexistence (x = 0.14) to 0.6 ± 0.1 in the SC region with the maximum critical temperature (x = 0.15) at low temperatures and weak magnetic fields. This reduction suggests that the symmetry of carrier pairing changes at the boundary of the transition from the phase of antiferromagnetic ordering and spin density waves to the superconducting phase in the presence of antiferromagnetic spin fluctuations.

The dynamic rearrangement of the structure of vortex domain walls (DWs) in films with uniaxial in-plane anisotropy has been examined based on two-dimensional micromagnetic model simulation. The optimum computational region has been chosen; grids with up to 270 × 75 cells 3 nm in size have been used. The scenarios of dynamic rearrangement of the DW structure in strong fields (up to 450 Oe) and in films with thicknesses exceeding 100 nm have been revealed for the first time. The emergence of multivortex instantaneous distributions of magnetization upon an increase in the film thickness and the external field intensity have been established. The dependence of the critical field on the film thickness has been refined.

The effect of the multiplicity of frictional loading with a sliding synthetic diamond indenter at room temperature in an argon medium and the temperature of loading in the range of −196 to +250°C on the phase composition, fine structure, and micromechanical properties of the surface layer of metastable austenitic chromium-nickel steel has been studied. It has been established that the completeness of the strain-induced martensitic γ → α′ transformation in the surface layer of steel is determined by the loading multiplicity and temperature, as well as the level of strengthening grows with an increase in the frictional loading multiplicity, but weakly depends on the frictional treatment temperature. According to the microindentation data, the characteristics of the surface layer strength and resistance to elastic and plastic deformation are improved with an increase in the frictional loading multiplicity. Frictional treatment by scanning with a synthetic diamond indenter at room and negative temperatures provides high quality for the treated surface with a low roughness parameter (Ra = 80.115 nm), and an increase in the frictional loading temperature to 150–250°C leads to the development of a seizure and growth in Ra to 195–255 nm. Using transmission electron microscopy (TEM), it has been shown that frictional treatment results in the formation of nanocrystalline and fragmented submicrocrystalline structures of strain-induced α′-martensite (at a loading temperature of −196°C) and austenite (at a loading temperature of +250°C) in the surface layer of steel alongside with two-phase martensitic-austenitic structures (at a loading temperature of +20°C).

The effect of Al₃(Sc,Zr) dispersoids on the evolution of the cast Al-Mg-Sc-Zr alloy structure under multi-directional isothermal forging (MIF) has been investigated. The alloy, which has an equiaxed grain structure with a grain size of ~25 μm and contains dispersoids 5–10 and 20–50 nm in size after onestage (at 360°C for 6 h) and two-stage (360°C for 6 h + 520°C for 1 h) annealing, respectively, was deformed at 325°C (~0.65 T_m) up to cumulative strains of e = 8.4. In the initial stages of MIF, new fine (sub)grains surrounded by low-angle and high-angle boundaries (HABs) were formed near the initial grain boundaries. With increasing strain, the volume fraction and misorientation of these crystallites increased, which led to the replacement of a coarse-grained structure with a fine-grained one with a grain size of ~1.5-2.0 μm. Dynamic recrystallization occurred in accordance to a continuous mechanism and was controlled by the interaction of lattice dislocations and/or (sub)grain boundaries with dispersoids that effectively inhibited the migration of boundaries, as well as the rearrangement of lattice dislocations and their annihilation. The particle size and the density of their distribution significantly affected the parameters of the evolved structure; in an alloy with smaller particles, a structure with a smaller grain size and a larger HAB fraction developed.