V. S. Zhigalov

Solid-phase reactions, self-propagating high-temperature synthesis, and order-disorder phase transition in thin films

The results of experimental studies of self-propagating high-temperature synthesis in double-layer Cu/Au thin-film systems are presented. It is shown that the synthesis initiation temperature for a Cu/Au film is determined by the order-disorder phase-transition temperature in the Cu-Au system. The order-disorder transition temperature for thin films is found to be lower than for the bulky samples. It is assumed that the temperatures of initiation of solid-phase reactions in thin films can be associated with the structural phase-transition temperatures.

Self-propagating high-temperature synthesis and solid-phase reactions in bilayer thin films

Self-propagating high-temperature synthesis (SHS) in Al/Ni, Al/Fe, and Al/Co bilayer thin films is investigated. It is established that SHS is achieved in thin films at initiation temperatures 300–350° lower than in powders. The mechanism of SHS in thin films is similar to the process of explosive crystallization. It is shown that at the initial stage solid-phase reactions arising on the contact surface of condensate films can be self-propagating high-temperature synthesis. SHS could find application in different technologies for obtaining film components for microelectronics.

Solid-phase synthesis of solid solutions in Cu/Ni(001) epitaxial nanofilms

Solid-phase synthesis of solid solutions in the epitaxial Cu/Ni(001) bilayer film systems of compositions 3Cu: 1Ni, 1Cu: 1Ni, and 1Cu: 3Ni has been studied using the X-ray diffraction methods. The saturation magnetization and the magnetic crystallographic anisotropy constant on nickel vary in accordance with the solid solution formation. The initiation temperature of the solid solutions is about 350 °C and is independent of the Ni: Cu layer thickness ratio. The solid-phase synthesis of the solid solutions is presumably attributed to the transport of the Cu atoms to the epitaxial Ni(001) layer. It is found that the solid-phase synthesis in the Cu/Ni bilayer nanofilms and multilayers is determined by the spinodal decomposition in the Cu-Ni system.

Study of solid-state reactions and order-disorder transitions in Pd/α-Fe(001) thin films

The formation of the hard-magnetic ordered L10-FePd phase in thin bilayer Pd/α-Fe(001) films has been experimentally studied. Solid-state reactions initiated by thermal heating in bilayer Pd/α-Fe(001) films with a thickness of 50–60 nm (the atomic ratio Pd: Fe ≈ 50: 50) separated from the substrate have been studied using the in situ electron diffraction methods. It has been shown that the solid-state reaction between the palladium and iron layers in Pd/α-Fe(001) starts at 400°C with the formation of the disordered Fe-Pd phase. At 480°C, the ordered L10-FePd phase is formed. The order-disorder phase transition has been studied. It has been established that the transition of the ordered L10-FePd phase to the disordered FePd phase starts at 725°C. At 740°C, only the disordered FePd phase is present over the whole volume of the film. The observed temperature of the order-disorder phase transition is shifted from the equilibrium value by 35°C to higher temperatures. This effect is assumingly associated with the higher concentration of palladium atoms at the boundaries of the Fe-Pd crystal grains owing to the grain-boundary adsorption.

Phase transformations in the Mn-Ge system and in GexMn1 − x diluted semiconductors

Results of an X-ray diffraction study as well as magnetic and electrical measurements of the solid-state reactions in Ge/Mn polycrystalline films of an 80/20 atomic composition have been presented. It has been shown that the ferromagnetic Mn5Ge3 phase is formed first on the Ge/Mn interface after annealing at ∼120°C. The further increase in the annealing temperature to 300°C leads to the beginning of the synthesis of the Mn11Ge8 phase, which becomes dominating at 400°C. The existence of new structural transitions in the Mn-Ge system in the region of ∼120 and ∼300°C has been predicted on the basis of the presented results and results obtained earlier when studying solid-state reactions in different film structures. The supposition about the general chemical mechanisms of the synthesis of the Mn5Ge3 and Mn11Ge8 phases during the solid-state reactions in the Ge/Mn films of the 80/20 atomic composition and the phase separation in GexMn1 − x (x > 0.95) diluted semiconductors has been substantiated.

High-Pressure Phases in Nanocrystalline Co(C) Films Obtained by Pulsed Plasma Vaporization

The phase composition of nanocrystalline Co(C) films obtained by a new pulsed plasma vaporization technique was found by studying their atomic structure and magnetic properties. The films deposited at the substrate temperature T=50°C were of heterophase structure and consisted of a supersaturated solid Co(C) solution and the metastable Co3C carbide. The films obtained at T=150°C represented a mechanical mixture of the metastable Co3C and Co2C carbides. The metastable Co3C and Co2C carbides obtained in a nanocrystalline state were high-pressure phases (∼100 kbar). The thermal stability ranges of these metastable phases were determined.

Solid-state synthesis of the ZnO-Fe 3 O 4 nanocomposite: Structural and magnetic properties

The structural and magnetic properties of ZnO-Fe3O4 nanocomposites produced by the solid-state reaction Zn + 3Fe2O3 → ZnO + 2Fe3O4 upon annealing of Zn/α-Fe2O3 films under vacuum at a temperature of 450°C have been studied. Ferrimagnetic Fe3O4 clusters with an average grain size of 40 nm and a magnetization of ∼430 emu/cm3 at room temperature, which are surrounded by a ZnO layer with a large contact surface, have been synthesized. The magnetic characteristics of the ZnO-Fe3O4 nanocomposite in the temperature range of 10–300 K have been presented.

Solid-phase synthesis of Co7Sm2(110) epitaxial nanofilms: Structural and magnetic properties

The solid-phase synthesis of the Co7Sm2 and Co17Sm2 magnetically hard phases in Co/Sm/Co(110) epitaxial film systems has been experimentally investigated. The Co7Sm2 phase is first formed at the Sm/Co interface at a relatively low (∼300°C) temperature. As the annealing temperature increases to ∼450°C, the Co17Sm2(110) phase grows epitaxially on the Co7Sm2(110) phase. The saturation magnetization and biaxial anisotropy constant in the samples vary with the formation of the Co7Sm2 and Co17Sm2 phases. Investigations of the solid-phase synthesis in the nanofilms reveal the existence of a new structure phase transition at 300°C in the Co-Sm system with a high cobalt content.

Magnetic interaction between superparamagnetic particles in nanogranular cobalt films

A system of cobalt nanoparticles exhibits a transition from the superparamagnetic state into the state with cooperative magnetic ordering caused by the magnetic interaction between Co particles. It is shown that this transition can be used for obtaining nanogranular materials possessing soft magnetic properties at a large electric resistivity.

Solid-state synthesis in Ni/Fe/MgO(001) epitaxial thin films

Solid-state synthesis in Ni/Fe/MgO(001) bilayer epitaxial thin films has been studied experimentally. The phase sequence Fe/Ni→(∼350°C)Ni3Fe→(∼400°C)NiFe→(∼ 550°C)γpar is formed as the annealing temperature increases. The crystal structure in the invar region consists of epitaxially intergrown single-crystal blocks consisting of the paramagnetic γpar and ferromagnetic NiFe phases, which satisfy the orientation relationship [100](001)NiFe ∥ [100](001) γpar. It has been shown that the nucleation temperatures of the Ni3Fe, NiFe, and γpar phases coincide with the temperatures of solid-state transformations in the Ni-Fe system.