


Vol 118, No 5 (2017)
- Year: 2017
- Articles: 13
- URL: https://journals.rcsi.science/0031-918X/issue/view/10188
Electrical and Magnetic Properties
Magnetoresistive sensitivity and uniaxial anisotropy of spin-valve microstrips with a synthetic antiferromagnet
Abstract
Microobjects (strips) were formed by contact photolithography using Та/Ni80Fe20/Co90Fe10/Cu/Co90Fe10/Ru/Co90Fe10/Fe50Mn50/Ta spin-valves prepared by magnetron sputtering. A mutually perpendicular arrangement of uniaxial and unidirectional anisotropy axes in microobjects has been formed using two different thermomagnetic treatment regimes. The magnetoresistive sensitivity of spin valve and spin-valve-based microobject has been found to depend on the mutual arrangement of the easy magnetization axis and direction of magnetic field applied upon thermomagnetic treatment. The obtained data have been interpreted taking into account changes in the induced anisotropy and anisotropy due to the shape of the microobject.



Dynamics of the magnetic moment of small dipole lattices in an alternating field
Abstract
Dynamic modes of the total magnetic moment of the square dipole 2 × 2 and 3 × 3 lattices have been investigated in alternating magnetic field with the linear and circular polarization, the static magnetic field being perpendiculat to it. A way to observe the dynamics of regular, quasiperiodic, or chaotic precession of the magnetic moments of lattices with different mode attractors has been shown. The effect of static field orientation and the type of anisotropy on the resonance dynamics has been studied.



Mechanical and magnetic properties of alloys near the concentration range of the existence of Co3(Al,W) intermetallic compound
Abstract
An experimental study of the mechanical and magnetic properties of Co–8 at % Al–X at % W (where Х = 4.6; 6.8; 8.5; 10; 12) polycrystalline alloys has been carried out depending on the tungsten content. It has been shown that an increase in the tungsten content induces the following changes: Young’s modulus changes from 240 to 259 GPa and the microhardness HV changes from 290 to 413 MPa. The Curie temperature of the intermetallic γ' phase (L12) grows from 1025 to 1049 K, and the saturation magnetization of the alloys decreases. The value of the coercive force also increases, from 1 to 500 Oe. The calculations of the specific heat of the γ' (L12)–γ (dcc) phase transition has shown that the highest amount of heat (304 J/g) is absorbed upon the phase transition in the sample containing the largest amount of tungsten (12.6 at %). The results obtained indicate the diffusion character of the transition, the rate of which is controlled by the diffusion of the slowest component of the alloy (in this case, tungsten). It has been found that the solvus temperature of the γ' phase increases from 1009 to 1044°С with an increase in the tungsten content from 4.6 to 12.6 at %.



Influence of asymmetric pinning of vortex domain walls on the magnetization curve of films with in-plane anisotropy
Abstract
A hysteresis loop shifted relative to the zero field in a fragment of a 100-nm-thick film with inplane anisotropy has been calculated based on a three-dimensional micromagnetic simulation. The reason for the revealed effect is an asymmetric pinning of a vortex domain wall by regions with enhanced values of the saturation magnetization and anisotropy constant.



Structure, Phase Transformations, and Diffusion
Synthesis of TiCr2 intermetallic compound from mechanically activated starting powders via calcio-thermic co-reduction
Abstract
Effect of mechanical activation of TiO2 and Cr2O3 oxides as starting materials was investigated for direct synthesis of TiCr2. Differential thermal analysis (DTA) indicated that increasing the ball milling time resulted in lower exothermic reaction temperatures between molten Ca–Cr2O3 and molten Ca–TiO2. A model-free Kissinger type method was applied to DTA data to evaluate the reaction kinetics. The results reveal that the activation energy of the exothermic reactions decreased with increasing the milling time. The structure, oxygen content, and average particle sizes of the obtained TiCr2 product were affected by the ball milling time of the starting materials. Increasing the milling time from 10 to 40 h decreased the average particle size and oxygen content of the obtained TiCr2 from 10 to 2 μm and from 1690 to 1290 ppm, respectively. The X-ray diffraction (XRD) results showed that TiCr2 compounds with metastable bcc phase can be produced using nano-sized starting materials, while only a slight amount of bcc phase can be obtained in the TiCr2 compounds, using micron-sized starting materials. The TiCr2 obtained by this method had a hydrogen absorption capability of 0.63 wt % and the kinetics of the hydrogen absorption increased for the 40 h milled sample.



Estimate of the applicability of Pd–Pt nanoalloy for data recording by the method of phase change
Abstract
Based on the computer simulation, the applicability of using individual nanoclusters of Pt, Pd, and particles of the Pd–Pt nanoalloy as unites of storage of data bits in nonvolatile memory devices, store capability of which is based on the principle of the phase change of the state of the carrier of information, has been estimated. To this end, the temperature and size limits of stability of different internal structures of nanoparticles in the course of the heating (to melting) and subsequent solidification (crystallization) with different rates of heat removal have been established. The results of the computer simulation of the nanoparticles of chemically pure platinum, palladium, and their alloy with different content of Pt atoms have been compared. It has been concluded that the best material for the memory cells the store capability of which is based on the occurrence of phase transitions is the nanoclusters of the Pd–Pt alloy with 10% platinum with a diameter D ≥ 3.5 nm.



Size dependence of the phase composition of silver nanoparticles formed by the electric explosion of a wire
Abstract
Transmission electron microscopy, selected-area electron diffraction, and high-resolution transmission electron microscopy (HRTEM) have been used to determine the morphological and phase features of silver nanoparticles synthesized by a physical method of electric explosion of silver wires. In the nanoparticles obtained, the presence of a hexagonal phase was detected besides the cubic phase and the size dependence of the phase composition of the nanoparticles has been revealed; all particles smaller than 25 nm only had a hexagonal structure, particles with sizes of 25–30 nm contained both the hexagonal and cubic phases, and particles larger than 30 nm had only a cubic structure. Based on an analysis of the conditions of synthesis of silver nanoparticles, an attempt to explain the mechanism of the stabilization of the hexagonal phase depending on the particle size was undertaken.



The process of crystallization from amorphous state in ribbons of Fe–Si–B–based alloys under the effect of a high DC magnetic field
Abstract
The effect of a high dc magnetic field (up to 29 T) applied during the crystallizing annealing of amorphous ribbons on the structure of Fe81Si7B12 and Fe73.5Cu1Nb3Si13.5B9 alloys has been studied. In the Fe81Si7B12 alloy, an increase in the average size of grains that form during magnetic annealing has been revealed; in the Fe73.5Cu1Nb3Si13.5B9 alloy, a small decrease is observed in the average grain size. The possible reason for this may be the differences in the specific features of the processes of crystallization of these alloys. No effect of the magnetic field on the crystallographic orientation of the arising grains has been revealed.



Strength and Plasticity
Role of the structural state of a copper–beryllium alloy in the formation of its tribotechnical properties
Abstract
The influence of the structural state of a copper–beryllium alloy on its resistance to friction fracture under adhesion interaction and abrasive wear has been investigated. It has been shown that the elastic interphase deformations that cause the tension of the crystal lattice of the particles of precipitated phase brings about a decrease in the wear resistance of the alloy at a retained high hardness. The relaxation of interphase deformations during the aging process leads to a significant increase in the wear resistance of the alloy, despite the reduction its hardness.



Effect of impurities of Fe and Si on the structure and strengthening upon annealing of the Al–0.2% Zr–0.1% Sc alloys with and without Y additive
Abstract
The effect of impurities of Fe and Si on the microstructure and kinetics of the change in the hardness during annealing of the cast Al–0.2% Zr–0.1% Sc and Al–0.2% Zr–0.1% Sc–0.2% Y alloys has been studied. It has been found that the presence of the impurities of Fe and Si in the Al–0.2% Zr–0.1% Sc alloy leads to a partial binding of scandium into the (Al, Fe, Si, Sc) and (Al, Fe, Sc) phases of crystallization origin and to the corresponding depletion of the aluminum solid solution of Sc. It has been shown that as a result, the strengthening is significantly decreases upon annealing. The addition of 0.2% Y into the Al–0.2% Zr–0.1% Sc alloy with impurities of Fe and Si leads to the formation of the Al3Y and (Al, Y, Fe, Si) phases, whereas Sc is completely dissolved in the aluminum solid solution. It has been shown that the addition of Y leads to an increase in the thermal stability of the alloys during annealing at temperatures of 250, 300, and 370°C and eliminates the negative effect of impurities of Fe and Si.



Influence of the parameters of a high-frequency acoustic wave on the structure, properties, and plastic flow of metal in the zone of a joint of materials welded by ultrasound-assisted explosive welding
Abstract
The results of an investigation of the influence of the parameters of high-frequency acoustic wave on the structure and properties of the zone of joint of homogeneous metals bonded by explosive welding under the action of ultrasound have been presented. The influence of the frequency and amplitude of ultrasonic vibrations on the structure and properties of the explosively welded joints compared with the samples welded without the application of ultrasound has been established. The action of high-frequency acoustic waves on the metal leads to a reduction in the dynamic yield stress, which changes the properties of the surface layers of the metal and the conditions of the formation of the joint of the colliding plates upon the explosive welding. It has been shown that the changes in the length and amplitude of waves that arise in the weld joint upon the explosive welding with the simultaneous action of ultrasonic vibrations are connected with a decrease in the magnitude of the deforming pulse and time of action of the compressive stresses that exceed the dynamic yield stress beyond the point of contact.



Structure and creep of Russian reactor steels with a BCC structure
Abstract
The structural phase transformations have been revealed and the characteristics of the creep and long-term strength at 650, 670, and 700°C and 60–140 MPa have been determined in six Russian reactor steels with a bcc structure after quenching and high-temperature tempering. Creep tests were carried out using specially designed longitudinal and transverse microsamples, which were fabricated from the shells of the fuel elements used in the BN-600 fast neutron reactor. It has been found that the creep rate of the reactor bcc steels is determined by the stability of the lath martensitic and ferritic structures in relation to the diffusion processes of recovery and recrystallization. The highest-temperature oxide-free steel contains the maximum amount of the refractory elements and carbides. The steel strengthened by the thermally stable Y–Ti nanooxides has a record high-temperature strength. The creep rate at 700°C and 100 MPa in the samples of this steel is lower by an order of magnitude and the time to fracture is 100 times greater than that in the oxide-free reactor steels.



Interactions between radiation defects and interstitial impurities in nickel microalloyed with carbon and Boron under electron and neutron irradiation
Abstract
Complex investigations have been carried out of the radiation damage of nickel alloys microalloyed with interstitial carbon and boron impurities under cascadeless electron and cascade neutron irradiation. Boron’s contribution to the resistivity has been found and the binding energy of a vacancy with boron atom has been determined to be 0.2 eV. The main mechanisms of radiation-induced structural and phase changes have been revealed.


