Vol 55, No 9 (2019)

This paper presents an analytical review that addresses physicochemical principles underlying the synthesis of granular structures in semiconductor–ferromagnet systems. Such systems comprise a II–IV–V₂, II₂–V₃, or II–V₂ compound as a semiconductor and MnAs as a ferromagnet. We demonstrate that granular magnetic structures are an alternative to superlattices in spintronic devices and can exhibit giant magnetoresistance and tunneling magnetoresistance effects. It is shown that, owing to the high carrier mobility in semiconductors, they are more attractive as matrices of granular materials than are metals or dielectrics. We have formulated the basic principles underlying the synthesis of granular structures with high magnetoresistance based on eutectic systems. Eutectic crystallization involves simultaneous crystallization of all the constituent phases, leading to the formation of an unusual, fine structure. High cooling rates are favorable for metastable crystallization. This causes a synergistic effect, stimulating nanostructuring and favoring the formation of granular structures. We present results on semiconductor–ferromagnet systems and demonstrate the possibility of producing granular magnetic structures with high magnetoresistance in such systems.

Thin (~50 nm) cadmium arsenide films have been grown by magnetron sputtering on single-crystal silicon and sapphire substrates. Using X-ray diffraction, scanning electron microscopy, atomic force microscopy, and Raman spectroscopy, the composition of the films has been shown to correspond to the Cd₃As₂ stoichiometry. Along with the α-Cd₃As₂ phase, the films contained trace levels of the α'-Cd₃As₂ phase. Annealing at 520 K led to recrystallization and the formation of [112] textured films on single-crystal silicon substrates. In the annealed films, the crystallite size evaluated using the Debye–Scherrer equation was ~30 nm.

The GaSb〈Mn〉 magnetic semiconductor has been studied using the visualization and analysis of electron-microscopic images of the material, an approach widely used in practice in making ultrastrong permanent magnets based on metallic alloys. The role of columnar magnetic crystals is assigned to manganese-decorated dislocations, and the role of a nonmagnetic matrix is played by the GaSb compound semiconductor. The material synthesized in this study has been characterized by X-ray diffraction, scanning electron microscopy, and magnetic measurements. The magnetization of a polished transverse section of GaSb〈Mn〉 has been analyzed as a function of the angle it makes with the magnetic flux direction and as a function of temperature in the range 4–300 K.

We have studied the growth of zinc selenide layers on flat and shaped indium phosphide surfaces. The growth rate of zinc selenide has been shown to depend on substrate orientation. It has been shown that the present results can be useful in designing mesa stripe structures for quantum electronic instruments. We have fabricated mesa stripe laser diodes operating on the absorption band of methane and suitable for producing fiber-optic signal transmission systems.

MnO₂ surface layers and the addition of Mn₃(PO₄)₂ through the gas phase have an advantageous combined effect on the thermal oxidation of InP, increasing the growth rate of the oxide film, ensuring rapid chemical binding of the indium, blocking its diffusion into the film, and activating phosphate formation processes, which leads to the formation of dielectric nanofilms with resistivity as high as 10¹⁰ Ω cm.

We propose a mechanism capable of describing phase transformations during the hydrothermal treatment of micron- and nanometer-sized γ-Al₂O₃ and Al(OH)₃ powders, identify the steps of the process, and demonstrate the role of water with a small heat of vaporization in the hydrothermal treatment process.

This paper presents a comparative analysis of the electrochemical and semiconductor properties of magnetite on a semiconductor/electrolyte interface. It is shown that the solid phase of the oxide has a bulk zone that leads to charge and potential distributions in both the bulk phase and electrolyte solution. The presence of a bulk zone on the magnetite surface is evidenced by the observed linear behavior of 1/C² as a function of E (where C is capacitance and E is potential).

The R₂Ge₂O₇ (R = Pr–Lu, Y) rare-earth germanates have been prepared by solid-state reactions by firing stoichiometric R₂O₃ + GeO₂ mixtures in air at temperatures in the range 1273–1473 K. The unit-cell parameters (a, c, and V) of the R₂Ge₂O₇ (R = Tb–Lu) compounds have been shown to be linear functions of the ionic radius of the rare-earth elements. The high-temperature heat capacity of polycrystalline samples of the germanates has been determined by differential scanning calorimetry in the temperature range 350–1000 K. The variation in the specific heat of R₂Ge₂O₇ has been shown to be correlated with the dependence of the heat capacity of rare-earth oxides on the ionic radius of the rare-earth element within each tetrad.

Polycrystalline praseodymium orthoniobate, PrNbO₄, has been studied by high-temperature X‑ray diffraction and differential scanning calorimetry. We have determined the temperature of the fergusonite–scheelite structural phase transition and shown it to be a second-order transition.

This paper presents results of a study aimed at developing physicochemical principles of tin diiodide (SnI₂) synthesis and ultrapurification by high-temperature fractional distillation. SnI₂ samples were synthesized by different processes: in solution, from elemental mixtures at atmospheric pressure, and in a vacuum. Next, the samples were purified by fractional distillation in a plate column. Separation factors of difficult-to-remove impurities in the SnI₂-based liquid–vapor system have been determined experimentally. We have prepared and characterized extrapure-grade SnI₂ containing 10 ppm by weight of trace impurities