Study of the mechanisms of the solid-state reactions in Sn/Fe/Cu thin films is interesting both from a fundamental point of view and from a view of the importance of emerging intermetallics in the technology of solder joints and thin-film lithium-ion batteries. By the integrated approach, including both X-ray phase analysis and local elemental analysis of the cross-sections of the films, the phase composition and the mutual arrangement of phases were studied, at various stages of the solid-state reaction occurring at different temperatures. The observed sequence of the appearing phases differs significantly from the expected one if the mass transfer took place by a volume diffusion through the forming layers.

Here we first report on the formation of epitaxial D03-Fe3Rh(001) films grown during solid-state reaction in Rh/Fe(001) bilayers on MgO(001) substrates. Samples of the Fe68Rh32 composition above 400 degrees C showed the formation of a new ordered phase, in addition to the ordered B2-FeRh phase (space group Pm-3m, lattice constant a = 0.2993 nm), which becomes the dominant phase in Fe76Rh24 samples. These results and the results of the asymmetrical XRD phi-scan prove that the new ordered phase is the ordered D03-Fe3Rh(001) phase (space group Fm-3m, lattice constant a = 0.5888 nm), forming a cube-on-cube orientation relationship with respect to the MgO(001) substrate. The D03-Fe3Rh sample is a soft magnetic material with high saturation magnetization.

Study of the mechanisms of the solid-state reactions in Sn/Fe/Cu thin films is interesting both from a fundamental point of view and from a view of the importance of emerging intermetallics in the technology of solder joints and thin-film lithium-ion batteries. By the integrated approach, including both X-ray phase analysis and local elemental analysis of the cross-sections of the films, the phase composition and the mutual arrangement of phases were studied, at various stages of the solid-state reaction occurring at different temperatures. The observed sequence of the appearing phases differs significantly from the expected one if the mass transfer took place by a volume diffusion through the forming layers.

The A2, B2, D0(3) phases and dispersive nanoprecipitates play key roles in the nature of super-functional properties, such as the large and sensitive magnetostriction, in Fe100-xGax alloys. However, the temperature conditions for the occurrence of the chemical interaction between Fe and Ga, leading to the synthesis of these phases and nanoprecipitates, remain completely unexplored. Herein we first report results of the start of the chemical interaction at the Ga/Fe(001) interface and the structural and magnetic phase transformations in 24Ga/76Fe (001), 40Ga/60Fe(001) and 60Ga/40Fe(001) bilayers from room temperature to 800.C. For all bilayers the magnetic ordered D0(3) phase is the first phase which is formed at the Ga/Fe(001) interface at similar to 375 degrees C. When the annealing temperature is increased above 580 degrees C in 24Ga/76Fe(001) samples the epitaxial D0(3)(001) layer begins to develop into the epitaxial magnetic ordered B2(001) layer, which remains after annealing to 800 degrees C. In 40Ga/60Fe(001) samples the epitaxial D0(3)(001) layer evolves into the epitaxial B2(001) layer and a new epitaxial layer with interplanar spacing 0.1484 nm (L6(0)(')), which has close reflections with L6(0) nanoprecipitates. The L6(0)(') phase exhibits unique magnetic properties, including a large magnetic fourfold anisotropy constant of similar to 7.10(5) erg/cm(3) and 8-fold anisotropy. The solid-state reactions in 60Ga/40Fe(001) samples start with the synthesis of D0(3) nanograins embedded in amorphous phases, whose peaks are centered on D0(3)(004) and Fe(002) reflections. Above 700 degrees C the amorphous phases partially crystallize and the epitaxial magnetic L6(0)' and ordered B2(001) phases emerge. Dewetting and unidentified secondary precipitations are observed in all samples and their influence on the magnetic properties is discussed. Our results demonstrate not only the complex nature of initial stage Fe100-xGax alloy synthesis, but also predict the low-temperature transformation at similar to 375 degrees C in the Fe - Ga phase diagram.

The formation of the Cu6Sn5 intermetallic in Sn(55nm)/Cu(30nm) thin-film bilayers has been studied upon heating the film sample from room temperature to 300°C directly in a column of a transmission electron microscope in the electron diffraction mode with recording electron diffraction patterns. The thin films synthesized by the solid-state reaction have been found to be single-phase and consist of the η-Cu6Sn5 hexagonal phase (95‒260°C). It has been suggested basing on the effective interdiffusion coefficient (5 × 10‒16 m2/s) estimated in the course of the reaction that the main mechanism of the formation of the Cu6Sn5 thin films is diffusion along grain boundaries and dislocations.

The phase formation sequences in 9Sn/91Fe(001) and 25Sn/75Fe(001) bilayers during thin-film solid-state reactions up to 800°C were investigated using X-ray diffraction, the torque method, and scanning electron microscopy. In both samples, FeSn2, FeSn, α-Fe1−xSnx, Fe5Sn3, α-Fe, and β-Sn were sequentially formed at the initiation temperatures Tini ~ 150°C, ~ 300°C, ~ 550°C, ~ 600°C, and ~ 700°C, respectively. Low-temperature transformations were predicted at temperatures TK1 ~ 150°C and TK2 ~ 300°C, which are absent in the phase equilibrium diagram of the Fe–Sn system. Solid-state dewetting of the 9Sn/91Fe(001) and 25Sn/75Fe(001) bilayers started at temperatures above 550°C. Overall, this work sheds new light on general chemical mechanisms governing the synthesis of intermetallic phases in Sn/Fe(001) thin films, the phase transformations, and the evolution of the dewetting process of FexSn1−x films.

The study of the formation of the Cu6Sn5 intermetallic compound in Sn(55nm)/Cu(30nm) thin bilayer films was carried out directly in the column of a transmission electron microscope (electron diffraction mode) by heating the film sample from room temperature to 300 °C and recording the electron diffraction patterns. The thin films formed as a result of a solid state reaction were monophase and consisted of the η-Cu6Sn5 hexagonal phase. The temperature range for the formation of the η-Cu6Sn5 phase was determined. The estimate of the effective interdiffusion coefficient of the reaction suggests that the main mechanism for the formation of the Cu6Sn5 intermetallic is diffusion along the grain boundaries and dislocations.

The structure and magnetic properties of CoPt–Al2O3 nanocomposite films synthesized by the annealing of Al/(Co3O4 + Pt) bilayers on a MgO(001) substrate at 650°C in vacuum are investigated. The synthesized composite films contain ferromagnetic CoPt grains with an average size of 25–45 nm enclosed in a nonconducting Al2O3 matrix. The saturation magnetization (Ms ~ 330 G) and coercivity (Hc ≈ 6 kOe) of the films are measured in the film plane and perpendicular to it. The obtained films are characterized by a spatial rotational magnetic anisotropy, which makes it possible to arbitrarily set the easy magnetization axis in the film plane or perpendicular to it using a magnetic field stronger than the coercivity (H > Hc).

We reported the phase formation sequences in 50Pt/50fcc-Co(001) and 32Pt/68fcc-Co(001) thin films after annealing up to 850 degrees C. In both cases, the ordered L1(0 )phase formed first on the Pt/Co interface at similar to 400 degrees C and as the annealing temperature increased the L1(0) phase transformed into the chemically disordered fcc Al phase in 50Pt/50fcc-Co(001) at 750 degrees C and in 32Pt/68fcc-Co(001) films at 550 degrees C. Based on the analysis of solid-state reactions in thin films, a phase transition at similar to 400 degrees C is predicted in Co-Pt systems with a 32-72% Pt composition. Torque measurements of the 50Pt/50fcc-Co(001) samples showed that the rotatable magnetic anisotropy coexisted with the three variants of L1(0) in a temperature range of 400-750 degrees C. An analysis of the torque curves revealed that the L1(0) films consist of a soft magnetic layer epitaxially intergrown to the substrate MgO(001) and a top layer having rotatable magnetic anisotropy. It showed that the magnetically hard properties of L1(0) films are associated with a rotatable magnetic anisotropy layer. A model of rotatable magnetic anisotropy is reasoned, which is founded on some identical mechanisms of rotatable magnetic anisotropy and magnetic-field-induced strains, explaining the ferromagnetic shape-memory effect in Heusler alloys. Our results suggested that the rotatable magnetic anisotropy phenomena may have an important role in the origin of perpendicular anisotropy in hard magnetic L1(0) structures. (C) 2020 Elsevier B.V. All rights reserved.

Here we first report results of the start of the solid-state reaction at the Rh/Fe(001) interface and the structural and magnetic phase transformations in 52Rh/48Fe(001), 45Rh/55Fe(001), 68Rh/32Fe(001) bilayers from room temperature to 800 °C. For all bilayers the non-magnetic nanocrystalline phase with a B2 structure (nfm-B2) is the first phase that is formed on the Rh/Fe(001) interface near 100 °C. Above 300 °C, without changing the nanocrystalline B2 structure, the phase grows into the low-magnetization modification αlʹ (MSl ~ 825 emu/cm3) of the ferromagnetic αʹ phase which has a reversible αlʹ ↔ αʺ transition. After annealing 52Rh/48Fe(001) bilayers above 600 °C the αlʹ phase increases in grain size and either develops into αhʹ with high magnetization (MSh ~ 1,220 emu/cm3) or remains in the αlʹ phase. In contrast to αlʹ, the αhʹ ↔ αʺ transition in the αhʹ films is completely suppressed. When the annealing temperature of the 45Rh/55Fe(001) samples is increased from 450 to 800 °C the low-magnetization nanocrystalline αlʹ films develop into high crystalline perfection epitaxial αhʹ(001) layers, which have a high magnetization of ~ 1,275 emu/cm3. αhʹ(001) films do not undergo a transition to an antiferromagnetic αʺ phase. In 68Rh/32Fe(001) samples above 500 °C non-magnetic epitaxial γ(001) layers grow on the Fe(001) interface as a result of the solid-state reaction between the epitaxial αlʹ(001) and polycrystalline Rh films. Our results demonstrate not only the complex nature of chemical interactions at the low-temperature synthesis of the nfm-B2 and αlʹ phases in Rh/Fe(001) bilayers, but also establish their continuous link with chemical mechanisms underlying reversible αlʹ ↔ αʺ transitions.

AbstractThe structural and magnetic properties of granular Co–In_2O_3 nanocomposite films formed by vacuum annealing of In/Co_3O_4 film bilayers at a temperature of 550°C have been investigated. The synthesized Co–In_2O_3 films contain ferromagnetic cobalt nanoclusters with an average size of 60 nm and a magnetization of ~340 emu/cm^3 surrounded by the In_2O_3 layer and exhibit the thermally activated conductivity.

The structural and magnetic properties of granular Co–In2O3 nanocomposite films formed by vacuum annealing of In/Co3O4 film bilayers at a temperature of 550°C have been investigated. The synthesized Co–In2O3 films contain ferromagnetic cobalt nanoclusters with an average size of 60 nm and a magnetization of ~340 emu/cm3 surrounded by the In2O3 layer and exhibit the thermally activated conductivity.

AbstractIt is shown that annealing 550°C of the Fe/Pt bilayer films fabricated by layer-by-layer deposition onto polycrystalline Al_2O_3 substrates in an atomic ratio of Fe: Pt = 71: 29 leads to the formation of the inplane rotational magnetic anisotropy with the easy axis that can be aligned by magnetic field in any direction in the film plane. The increase in the Pt content in the investigated film system to 50 at % leads to an increase in the anisotropy constant to 6.5 × 10^6 erg/cm^3, which exceeds the value in the Fe_71Pt_29 sample by a factor of 6. In addition to the rotational anisotropy, the Fe50Pt50 films are characterized by the perpendicular rotational magnetic anisotropy, which is higher than the film shape anisotropy. Therefore, the easy axis in these samples can be aligned by magnetic field in any spatial direction. According to the X-ray and magnetic measurement data, the synthesized samples have a polycrystalline structure consisting of two ordered phases: magnetically hard L1_0–FePt and magnetically soft L1_2–Fe_3Pt. This gives us grounds to suggest that the rotational magnetic anisotropy originates from the epitaxial intergrowth and exchange coupling of these two phases.

It is shown that annealing 550°C of the Fe/Pt bilayer films fabricated by layer-by-layer deposition onto polycrystalline Al2O3 substrates in an atomic ratio of Fe: Pt = 71: 29 leads to the formation of the inplane rotational magnetic anisotropy with the easy axis that can be aligned by magnetic field in any direction in the film plane. The increase in the Pt content in the investigated film system to 50 at % leads to an increase in the anisotropy constant to 6.5 × 106 erg/cm3, which exceeds the value in the Fe71Pt29 sample by a factor of 6. In addition to the rotational anisotropy, the Fe50Pt50 films are characterized by the perpendicular rotational magnetic anisotropy, which is higher than the film shape anisotropy. Therefore, the easy axis in these samples can be aligned by magnetic field in any spatial direction. According to the X-ray and magnetic measurement data, the synthesized samples have a polycrystalline structure consisting of two ordered phases: magnetically hard L10–FePt and magnetically soft L12–Fe3Pt. This gives us grounds to suggest that the rotational magnetic anisotropy originates from the epitaxial intergrowth and exchange coupling of these two phases.

Mn5Ge3 films are promising materials for spintronic applications due to their high spin polarization and a Curie temperature above room temperature. However, non-magnetic elements such as oxygen, carbon and nitrogen may unpredictably change the structural and magnetic properties of Mn5Ge3 films. Here, we use the solid-state reaction between Mn and GeO thin films to describe the synthesis and the structural and magnetic characterization of Mn5Ge3(Mn5Ge3Oy)-GeO2(GeOx) nanocomposite materials. Our results show that the synthesis of these nanocomposites starts at 180°С when the GeO decomposes into elemental germanium and oxygen and the resulting Ge atoms immediately migrate into the Mn layer to form ferromagnetic Mn5Ge3 nanoclusters. At the same time the oxygen atoms take part in the synthesis of GeOx and GeO2 oxides and also migrate into the Mn5Ge3 lattice to form Mn5Ge3Oy Nowotny nanoclusters. Magnetic analysis assumes the general nature of the Curie temperature increase in carbon-doped Mn5Ge3Cx and Mn5Ge3Oy films. Our findings prove that not only carbon, but oxygen may contribute to the increase of the saturation magnetization and Curie temperature of Mn5Ge3-based nanostructures.

AbstractThe results of structural and magnetic investigations of nanogranular Co–Al_2O_3 films formed from Co_3O_4/Al thin-film layered structures upon vacuum annealing are reported. The Co_3O_4/Al films have been obtained by sequential reactive magnetron sputtering of a metallic cobalt target in a medium consisting of the Ar + O_2 gas mixture and magnetron sputtering of an aluminum target in the pure argon atmosphere. It is shown that such a technique makes it possible to obtain nanogranular Co–Al_2O_3 single- and multilayer thin films with a well-controlled size of magnetic grains and their distribution over the film thickness.

The results of structural and magnetic investigations of nanogranular Co–Al2O3 films formed from Co3O4/Al thin-film layered structures upon vacuum annealing are reported. The Co3O4/Al films have been obtained by sequential reactive magnetron sputtering of a metallic cobalt target in a medium consisting of the Ar + O2 gas mixture and magnetron sputtering of an aluminum target in the pure argon atmosphere. It is shown that such a technique makes it possible to obtain nanogranular Co–Al2O3 single- and multilayer thin films with a well-controlled size of magnetic grains and their distribution over the film thickness.

The phase formation sequence during the thermally induced solid-state reaction between polycrystalline Pt and epitaxial fcc-Co (001) films in the Pt/fcc-Co(001) bilayers are systematically examined using X-ray diffraction and magnetic measurements. The films have nominal atomic ratio Co:Pt = 28:72 and total thickness 300-400 nm. Annealing to the temperature of 375 degrees C does not change the structural and magnetic properties of the films; this is indicative of the absence of considerable mixing at the Co/Pt interface. With the subsequent increase of the annealing temperature, the phase formation in the Pt/fcc-Co( 001) bilayers has been found to have two temperature (375 degrees C-575 degrees C and 575 degrees C-825 degrees C) intervals. Solid-state reaction between Pt and Co starts above 375 degrees C, and nanoclusters containing the ordered L1(0) phase epitaxially intergrow with the disordered A1 phase of the composition CoPt3 form and exist in the first temperature interval. The distinctive feature of the first interval is the formation of in-plane rotatable magnetic anisotropy. In the second temperature interval, the (L1(0) + A1) two-phase mixture grows into the ordered L1(2)-CoPt3 phase leading to the disappearance of rotatable anisotropy. Possible origin of the rotatable magnetic anisotropy is discussed. The first magnetocrystalline anisotropy constant of L12-CoPt3 has the maximum value of -5.0.10(5)egr/cm(3) and order parameter 0.55 at 675 degrees C. A careful analysis of thin film solid-state reactions implies the existence of low-temperature transformation (similar to 375 degrees C) on the Pt-rich side of the Co-Pt system. (C) 2017 Elsevier B.V. All rights reserved.

Представлены результаты исследования структурных и магнитных свойств пленок Fe87Pt13, синтезированных с использованием твердофазных реакций, и композитных пленок Fe87Pt13-Al2O3, полученных с помощью метода алюмотермии. Показано, что в синтезированных образцах обоих типов присутствует вращающаяся магнитная анизотропия, заключающаяся в том, что направление легкой оси намагничивания в плоскости пленки может устанавливаться магнитным полем. Установлено, что в композитных Fe87Pt13-Al2O3 пленках величина вращающейся магнитной анизотропии на порядок выше, чем в образцах Fe87Pt13. Сделано предположение, что природа вращающейся магнитной анизотропии связана с обменным взаимодействием L10-FePt фазы с L12-Fe3Pt фазой в пленках Fe87Pt13 и с магнитными окислами железа в образцах Fe87Pt13-Al2O3. Исследование выполнено при финансовой поддержке РФФИ в рамках научных проектов N 16-03-00069 и 15-02-00948, и частично правительства Красноярского края, КФН, РФФИ (проект N 16-42-243006). DOI: 10.21883/FTT.2017.02.44066.262