Kh. Ya. Mulyukov

Saturation magnetization and Curie temperature of nanocrystalline nickel

Abstract Bulk samples of nanocrystalline Ni were produced by severe plastic deformation consolidation of ball-milled powders. The processed samples are characterized by reduced values of saturation magnetization and Curie temperature. Relying on transmission electron microscopy and X-ray data, an assumption has been made to explain the origin of the observed phenomena.

THE CHANGE IN THE EFFECTIVE MAGNETIC MOMENT IN GADOLINIUM AFTER SEVERE PLASTIC DEFORMATION

Abstract This paper presents the results of an experimental study of the temperature dependence of the magnetization and paramagnetic susceptibility in pure gadolinium after severe plastic deformation. A significant decrease in the effective magnetic moment was established, which is explained on the basis of an analysis of the structural changes in the sample after deformation.

The study of domain structure of submicron grained cobalt and its changes during heating

Abstract The results of an experimental study of the domain structure of cobalt with a submicron-grained structure (d≈0.1 μm) at room temperature and during heating are given. For comparison the domain structure of coarse-grained (d = 10 μm) specimens are studied as well. It is established that the decrease of grain size in the structure slightly changes the shape of the domain structure of a striped type. At heating in the temperature range of 470–570 K, an increase of domain width is observed and then near 570 K the change of the domain wall direction by π/2 in the specimen plane occurs. The explanation of observed effects proceeding from the analysis of temperature dependence of cobalt magnetocrystalline anisotropy constants is given.

Magnetic hysteric properties and saturation magnetization of nanocrystalline iron

The paper presents the results of experimental studies of bulk nanocrystalline pure iron produced by two-steps severe plastic deformation. The processed samples are characterized by enhanced values of coercivity and saturation in comparison with a coarse grained state. Annealing leads to partial restoration of the properties. High-temperature (1073 K) annealing results in complete restorations of properties due to recrystallization. Transmission electron microscopy and X-ray analysis were used for structural analysis.

Thermal expansion of cobalt in various structural states

The temperature dependence of the thermal expansion of cobalt in various structural states was studied. It is shown that, in the temperature range wherein a coarse-grained sample elongates in a jumpwise manner, a sample with a nanocrystalline structure does not demonstrate such a behavior. The linear thermal expansion of the nanocrystalline sample over the entire temperature range of heating is explained by the fact that the hcp-fcc phase transformation does not occur in the nanocrystalline cobalt. The phase transformation occurs only after annealing of the nanocrystalline sample at 923 K for 30 min when the crystallites grow to a certain size. It is shown that the nanostructural state of cobalt is stable up to 793 K.

Effect of severe plastic deformation on the properties of the Fe-36% Ni invar alloy

Temperature dependences of the magnetization and thermal expansion coefficient of the Fe-36% Ni invar alloy in different structural states obtained upon plastic deformation by torsion under a quasihydrostatic pressure followed by annealing at different temperatures are studied. A decrease in the thermal expansion coefficient of the invar in a temperature range of 20–100°C and the formation of ordered precipitates (with a superstructure) were found to result from severe plastic deformation.

Thermal expansion of Ni2.08Mn0.96Ga0.96 alloy

The temperature dependence of the thermal expansion of polycrystalline Ni2.08Mn0.96Ga0.96 alloy samples is studied in the as-cast state and after homogenizing annealing. A sample in which twins are mainly oriented normal to the sample length shortens jumpwise during the martensitic transformation. A sample in which twins are parallel to its length elongates jumpwise. After annealing, both samples do not exhibit a jumplike change in length during the phase transformation. When an annealed sample is cooled in a magnetic field, its length again changes jumpwise in the phase transformation range.

Dilatation anisotropy upon the phase transition in the rolled Ti-49.8% Ni alloy

The temperature dependence of the thermal expansion of the Ti-49.8% Ni alloy rolled at 773 K has been measured in three mutually perpendicular directions with respect to the rolling direction. It has been found that, upon phase transition of the martensitic type, the sample is elongated stepwise in two directions, and it is contracted in the third direction. The observed effect is due to the crystallographic texture. The dilatation jump during the phase transformation is determined by the joint action of the change in lattice parameters and the process of twinning.

Magnetic properties of terbium with submicrocrystalline structure

The influence of the structural state of terbium on its magnetic properties is studied. It is shown that in the submicrocrystalline state remagnetization occurs following a wide hysteretic loop and a helical antiferromagnetic order does not form. Unlike the coarse-grained state, the magnetization value in the submicrocrystalline state is 5 times less, and the temperature of magnetic transformation is lower by 14 K.

Study of the domain structure of submicron-grained nickel

Abstract The results of an experimental study of the domain structure of nickel with submicron-grained structure ( d = 0.1 μm ) by the Lorenz method are given. For comparison, the domain structure of coarse-grained ( d = 10 μm ) specimens are studied as well. It is established that the decrease in grain size from 10 to 0.1 μm in the structure causes no changes in the domain structure configuration. The observations are explained from the analysis of nickel magneto-crystalline and induced anisotropies.