E. P. Naiden

Synthesis of Ti3Al and TiAl based surface alloys by pulsed electron-beam melting of Al(film)/Ti(substrate) system

Phase formation and surface hardening in the 100-nm-thick Al(film)/Ti(substrate) system under conditions of pulsed electron-beam melting (∼15 keV, ∼3 μs, 3–4 J/cm2) have been studied depending on the number of film deposition-melting cycles. Using this method, submicrocrystalline and nanocrystalline surface alloys with thicknesses ≥3 μm based on Ti3Al and TiAl intermetallics have been obtained on the titanium substrate.

Automatic Complex for a Study of the Characteristics of Hard Magnetic Materials

An automatic setup for a study of the magnetic characteristics of hexagonal oxide ferrimagnetic materials, which uses a technique of determining anisotropy fields by the singular-point detected method, is described.

Formation of silicon carbide and diamond nanoparticles in the surface layer of a silicon target during short-pulse carbon ion implantation

Synthesis of silicon carbide and diamond nanoparticles is studied during short-pulse implantation of carbon ions and protons into a silicon target. The experiments are carried out using a TEMP source of pulsed powerful ion beams based on a magnetically insulated diode with radial magnetic field Br. The beam parameters are as follows: the ion energy is 300 keV, the pulse duration is 80 ns, the beam consists of carbon ions and protons, and the ion current density is 30 A/cm2. Single-crystal silicon wafers serve as a target. SiC nanoparticles and nanodiamonds form in the surface layer of silicon subjected to more than 100 pulses. The average coherent domain sizes in the SiC particles and nanodiamonds are 12–16 and 8–9 nm, respectively.

Spin-orientation transitions in the system BaFe12−2xCoxTixO19

A neutronographic investigation of the system BaFe12−2xCoxTixO19 (0≤x <- 3.5), was conducted in the 77–800 K temperature interval. The distribution of Co2+ and Ti4+ ions in the crystallographic sublattices was calculated. A magnetic state diagram of the system was constructed in x-T coordinates, based on data from the temperature dependencies of the magnetic reflection intensities. It is shown that a state with a plane of easy magnetization exists in the given system only in narrow intervals of Co ion concentrations and temperatures. Features of the occurrence of spin reorientation in the investigated system are discussed.

Magnetization processes of the first kind in the hexaferrite Co0.62Zn1.38W

The magnetization curves M(H) and derivatives ∂2M/∂H2 of a polycrystalline textured specimen of the compound BaCo0.62Zn1.38Fe16O27 are investigated in the 100–300 K temperature range. It is shown that magnetization processes of the first kind are characteristic for this compound at temperatures below 220 K. The diagram of the magnetic state is analyzed in coordinates of the normalized anisotropy constants X=K2/K1 and Y=K3/K1. Temperature dependences of the three magnetic crystallographic anisotropy constants are computed on the basis of experimental data on the critical magnetization and the field, and hysteresis loop width.

Effect of conditions of pulsed electron-beam melting for Al (film)/Ti (substrate) systems on phase formation and properties of Ti-Al surface alloys

Findings of comparative investigations are presented for phase formation, characteristics of hardening, tribological properties, and oxidation resistance of Ti-Al intermetallic surface alloys formed by multiple alternation of deposition of an Al film (0.1–1 μm) on a Ti substrate and pulsed liquid-phase mixing of Al and Ti by intense low-energy (∼15 keV) electron beams with microsecond (∼3 μs) and submillisecond (100 μs) duration. It is found that microsecond synthesis is effective for formation of γ(TiAl) oxidation-resistant surface alloys. In turn, submillisecond synthesis allows one to form Ti3Al surface alloys with enhanced wear resistance.

Thermomagnetic phenomena in hexagonal ferrimagnetic materials

The results of an investigation of the magnetocaloric effect in the CoTi-M and CoZn-W hexaferrite systems in the 150–500 K temperature range are presented. It is shown that the maxima of the magnetocaloric effect correspond to spontaneous spin-orientational transitions leading to transformation of the magnetic structure from easy-plane to uniaxial and to resultant changes in the values and signs of the magnetic anisotropy constant as a function of the composition and temperature. Estimates of the ΔT(T) relation taking into account the magnetic anisotropy constants K1, K2, and K3, which are known for the compounds considered, agree well with experiment. Hence, the main contribution to the magnetocaloric effect at temperatures far from the Curie point in the materials in question is governed by the rotation of the magnetization vector.

Magnetic properties of hexagonal oxide ferrimagnets with orientational transitions

We study the magnetic structure of different types of hexaferrites, BaCoxTixFe12−2xO19(M), BaCo2−xZnxFe16O27(W), and Ba3Co2.4Ti0.4Fe23.2O41 (Z), and determine the concentration and temperature regions whre magnetically ordered phases such as the cone, plane, and axis of easy magnetization phases exist and the order of the magnetoorientational phase transitions. The constants of magnetic crystal anisotropy, including those of a higher order, were determined using polycrystalline textured samples. We estimate the exchange integrals for the main structural types of hexaferrites, M, W, Y, and Z. Based on these values, we show that it is possible to make a quite reliable prediction about the concentration and temperature dependence of such basic characteristics of hexaferrites as magnetization and anisotropy fields.

Method of a singular point and determination of fields of anisotropy of polycrystalline hexagonal magnets

A numerical computation is performed on the magnetization curves and their derivatives for magnets of hexagonal syngony for isotropic polycrystalline specimens as well as materials with “sheet” texture in the basis plane. It is shown that investigation of the second derivatives ∂2M/∂H2 for a degree of texture fT > 0.4 permits obtaining information about the magnitude of the anisotropy field independently of its type. The singularities of M(H) and ∂2M/∂H2 are examined for magnetization processes of the first kind. In this case the singular point method permits measuring the magnitude of the critical fields, the critical magnetizations, and the anisotropy field on a textured specimen with fT>0.7, which yields information about the magnitudes of the high order anisotropy constants in the long run.

Mechanochemical synthesis of nanodimensional ferrite powders from salt systems

Nanodimensional spherical powders of oxide cubic ferrimagnets are obtained by mechanochemical synthesis. Their phase composition, morphology, dispersity, specific surface, and magnetic properties are determined. It is established that the synthesized ferrites are nanodimensional powders with a highly developed surface (S = 100−160 m2/g), and their magnetic characteristics substantially differ from those for bulk ferrites. As the structural element is reduced from 1000 to ∼3–16 nm, ferrimagnets acquire the properties of cluster spin glass with a high blocking temperature.