[en] Magnetic properties of the Chelyabinsk meteorite were studied in a wide temperature range – up to ∼ 1300 K. The analysis shows that the meteorite contains ferromagnetic inclusions of both Fe-Ni alloy and pure iron. It has visually been demonstrated that iron inclusions of the Chelyabinsk meteorite experience no β→γ structural phase transformation. (paper)

[en] The magnetic properties of an EuBaCo_1.9O_5.36 single crystal are studied in the temperature range T = 2–300 K and the magnetic field range H ≤ 90 kOe. This binary layered cobaltite single crystal has vacancies in the cobalt and oxygen sublattices, in contrast to the stoichiometric EuBaCo₂O_5.5 composition. All cobalt ions in EuBaCo1.9O5.36 are in a trivalent state. The single crystal has an orthorhombic structure with space group Pmmm, and its unit cell parameters are a = 3.883 Å, b = 7.833 Å, and c = 7.551 Å. The field and temperature dependences of the magnetization of the single crystal demonstrate that it is ferrimagnet below T_C = 242 K. At T < 300 K, all three spin states of the Co³⁺ ions are present. The nearest-neighbor interactions give antiferromagnetic (AFM) and ferromagnetic (FM) contributions to the exchange energy. The ratio of the AFM to the FM contributions changes when temperature decreases because of a change in the spin state of the Co³⁺ ions. The single crystal exhibits signs of mictomagnetism at low temperatures in high magnetic fields. At T = 2 K and H = 90 kOe, the zero-field and nonzero-field magnetizations are strongly different because of a uniaxial magnetic anisotropy, which tends to set magnetization along the magnetic field applied in cooling throughout the crystal volume. As a result, a complex ferrimagnetic structure with a noncollinear direction of Co³⁺ spins appears. The following phenomena characteristic of mictomagnets are also observed in the EuBaCo_1.9O_5.36 single crystal: a shift in a magnetization hysteresis loop when temperature decreases, retained hysteretic phenomena and no magnetization saturation in high magnetic fields, and an orientation transition. The mictomagnetic state in EuBaCo_1.9O_5.36 is shown to be caused by the structural distortions induced by vacancies in the cobalt and oxygen sublattices and by the frustration of AFM and FM exchange interactions.

[en] The paper presents the results of experimental studies of vibro-mechanical mechanism of residual stresses relaxation in ringed parts. There was described the mechanism of vibro-mechanical relaxation that includes machining of ringed parts among three rotating rolls under pressure. This leads to multicyclic loading due to which there occurs relaxation of residual stresses. To study the process of vibro-mechanical relaxation a complete factorial experiment was carried out. As a result of experiments we obtained empirical dependence of residual stresses on processing factors. (paper)

[en] It is established that excess oxygen content δ influences the exchange bias (EB) in layered GdBa-Co₂O_5+δ cobaltite. The EB effect arises in p-type (δ > 0.5) cobaltite and disappears in n-type (δ < 0.5) cobaltite. The main parameters of EB in GdBaCo₂O_5.52(2) polycrystals are determined, including the field and temperature dependences of EB field H_EB, blocking temperature T_B, exchange coupling energy J_i of antiferromagnet–ferromagnet (AFM–FM) interface, and dimensions of FM clusters. The training effect inherent in systems with EB has been studied. The results are explained in terms of exchange interaction between the FM and AFM phases. It is assumed that the EB originates from the coexistence of Co³⁺ and Co⁴⁺ ions that leads to the formation of monodomain FM clusters in the AFM matrix of cobaltite.

[en] In the near future, the demand for autonomous kW-level electric power generating plants in the Arctic zone and in the Far East will number in the tens and hundreds. In the present article, the operational characteristics of radioisotope thermoelectric generators with direct conversion of heat into electricity, which are being decommissioned, are analyzed. Schemes for autonomous electric power plants based on renewable sources of energy and electrochemical cells are proposed as alternatives. The problems arising in the development of such plants are analyzed. The results achieved in meeting concrete orders from operating organizations are discussed. It is concluded that autonomous electric power plants with renewable sources of energy and fuel cells hold promise.

[en] The paper describes the mechanism of micro-cracks development in solid structural materials based on the theory of brittle fracture. A probability function of material cracks energy distribution is obtained using a probabilistic approach. The paper states energy conditions for cracks growth at material high-cycle loading. A formula allowing to calculate the amount of energy absorbed during the cracks growth is given. The paper proposes a high- cycle fatigue evaluation criterion allowing to determine the maximum permissible number of solid body loading cycles, at which micro-cracks start growing rapidly up to destruction. (paper)

[en] The appearance and growth of fatigue microcracks during the relaxation of residual stresses under the action of high-cycle loads is one of the main reasons of decreasing of durability of products. To reduce residual stress of the bearing rings, there was developed a technology on the basis of the cyclic elastic deformation instead of using energy-consuming thermal tempering. The technology consists of continuous running of the rings between three rollers under the load. A key feature of the technology is the controllability of cyclic loading of parts. The conducted study of an experimental batch of rings proved the reduction of residual stresses by more than 2 times in comparison with the average value of residual stresses after thermal tempering. (paper)

[en] The temperature dependence of the resistivity and magnetic moment of La_0.85Ba_0.15MnO₃ and La_0.85Sr_0.15MnO₃ manganite single crystals in magnetic fields up to 90 kOe is investigated. Analysis of the experimental results shows that the magnetoresistance of lanthanum manganites far from the Curie temperature T_C can be described quantitatively by the s-d model normally used for ferromagnets and taking into account only the exchange interaction between the spins of charge carriers and magnetic moments. These data also show that the features of lanthanum manganites responsible for colossal magnetoresistance (CMR) are manifested in a narrow temperature interval δT ≈ 20 K near T_C. Our results suggest a CMR mechanism analogous to the mechanism of giant magnetoresistance (GMR) observed in Fe/Cr-type multilayers with nanometer layer thickness. The nanostratification observed in lanthanum manganites and required for GMR can be described taking into account the spread in T_C in the CMR range δT.

[en] A method is proposed that allows one to divide the magnetoresistance (MR) observed in manganites into three mechanisms: dimensional, orientational, and magnetic. The first two mechanisms are associated with the stratification of a substance into ferromagnetic and nonferromagnetic phases, which significantly differ in electric resistivity. The dimensional mechanism of MR is attributed to the effect of a magnetic field on the size of magnetic inclusions. The orientational mechanism of MR is determined by the dependence of electric resistivity on the mutual orientation of the magnetizations of magnetic inclusions. The magnetic mechanism of MR is determined by the properties of the magnetization of a ferromagnet, in particular, by the Curie–Weiss singularity on the temperature dependence of magnetic susceptibility at the Curie point. This mechanism exists in homogeneous substances, although its value may depend on the magnetic properties of inhomogeneities. The method is developed for substances with activation-type conductivity and is applied to the analysis of MR of La_0_._8_5Sr_0_._1_5MnO_3 manganite near the Curie point, where the MR attains its maximum. The dimensional mechanism turns out to be dominant in magnetic fields H greater than the saturation field H_s (H > H_s). The orientational, dimensional, and magnetic mechanisms have a comparable effect on the MR for H < H_s. The effect of the orientational mechanism on MR is relatively weak (does not exceed the third part of the total MR), although this mechanism determines the giant MR in multilayered metal films. The possibility of application of the method to the analysis of MR near the insulator–metal transition is analyzed

[en] The article describes the results of experimental studies on ultrasonic stabilization of the bearing rings. The mean and root-mean-square values of non-roundness of the rings after ultrasonic and thermal treatment were compared. Comparative analysis showed that the root- mean-square deviation and the mean value of non-roundness after ultrasonic stabilization was lower than that after thermal stabilization. (paper)