We report here a simple hydrothermal synthesis of 100-200 nm flakes of tochilinite (Fe
1−
x
S)·
n
(Mg,Fe)(OH)
2
constructed by interchanging atomic sulfide and hydroxide sheets as a representative of ...a new platform of multifunctional two-dimensional materials. The reliable formation of tochilinites was ensured by an excess of sodium sulfide, with the assembly of the metal sulfide and hydroxide sheets driven by their opposite electric charges. X-ray photoelectron spectroscopy found that the hydroxide layers involved Fe
3+
cations from 10 to 40% of total iron tuned by addition of Al and Li entering the layers; the Fe
1−
x
S sheets comprised comparable amounts of high-spin Fe
3+
and Fe
2+
centers, and minor S-S bonding. The room-temperature Mössbauer spectra fitted with several doublets (chemical shift of 0.35-0.4 mm s
−1
and varying quadrupole splitting) transformed to three six-line patterns (hyperfine fields of ∼290, 350 and 480 kOe) due to magnetic ordering at 4.2 K, albeit the paramagnetic behavior observed in SQUID experiments. A series of UV-vis absorption maxima were explained in terms of both the high-index all-dielectric Mie resonance, in line with the permittivity measurement data, and the ligand-metal charge transfer resembling that in Fe-S clusters in proteins. Prospective properties and applications of the materials are discussed.
We report the reliable synthesis of 2D iron sulfide-magnesium hydroxide nanoflakes. The sulfide and hydroxide sheets assemble
via
opposite electric charges. Comparable amounts of high-spin Fe
3+
and Fe
2+
centers occur in the sulfide layers.
Three-layer iron-rich Fe3+xSi1−x/Ge/Fe3+xSi1−x (0.2 < x < 0.64) heterostructures on a Si(111) surface with Ge thicknesses of 4 nm and 7 nm were grown by molecular beam epitaxy. Systematic studies of ...the structural and morphological properties of the synthesized samples have shown that an increase in the Ge thickness causes a prolonged atomic diffusion through the interfaces, which significantly increases the lattice misfits in the Ge/Fe3+xSi1−x heterosystem due to the incorporation of Ge atoms into the Fe3+xSi1−x bottom layer. The resultant lowering of the total free energy caused by the development of the surface roughness results in a transition from an epitaxial to a polycrystalline growth of the upper Fe3+xSi1−x. The average lattice distortion and residual stress of the upper Fe3+xSi1−x were determined by electron diffraction and theoretical calculations to be equivalent to 0.2 GPa for the upper epitaxial layer with a volume misfit of −0.63% compared with a undistorted counterpart. The volume misfit follows the resultant interatomic misfit of |0.42|% with the bottom Ge layer, independently determined by atomic force microscopy. The variation in structural order and morphology significantly changes the magnetic properties of the upper Fe3+xSi1−x layer and leads to a subtle effect on the transport properties of the Ge layer. Both hysteresis loops and FMR spectra differ for the structures with 4 nm and 7 nm Ge layers. The FMR spectra exhibit two distinct absorption lines corresponding to two layers of ferromagnetic Fe3+xSi1−x films. At the same time, a third FMR line appears in the sample with the thicker Ge. The angular dependences of the resonance field of the FMR spectra measured in the plane of the film have a pronounced easy-axis type anisotropy, as well as an anisotropy corresponding to the cubic crystal symmetry of Fe3+xSi1−x, which implies the epitaxial orientation relationship of Fe3+xSi1−x (111)0−11 || Ge(111)1−10 || Fe3+xSi1−x (111)0−11 || Si(111)1−10. Calculated from ferromagnetic resonance (FMR) data saturation magnetization exceeds 1000 kA/m. The temperature dependence of the electrical resistivity of a Ge layer with thicknesses of 4 nm and 7 nm is of semiconducting type, which is, however, determined by different transport mechanisms.
The crystal structures of the first-synthesized compound EuScCuS3 and previously known SrScCuS3 are refined by Rietveld analysis of X-ray powder diffraction data. The structures are found to belong ...to orthorhombic crystal system, space group Cmcm, structural type KZrCuS3, with a = 3.83413(3) Å, b = 12.8625(1) Å, c = 9.72654(8) Å (SrScCuS3) and a = 3.83066(8) Å, b = 12.7721(3) Å, c = 9.7297(2) Å (EuScCuS3). The temperatures and enthalpies of incongruent melting are the following: Тm = 1524.5 К, ΔHm = 21.6 kJ•mol−1 (SrScCuS3), and Тm = 1531.6 К, ΔHm = 26.1 kJ•mol−1 (EuScCuS3). Ab initio calculations of the crystal structure and phonon spectrum of the compounds were performed. The types and wavenumbers of fundamental modes were determined and the involvement of ions participating in the IR and Raman modes was assessed. The experimental IR and Raman spectra were interpreted. EuScCuS3 manifests a ferromagnetic transition at 6.4 K. The SrScCuS3 compound is diamagnetic. The optical band gaps were found to be 1.63 eV (EuScCuS3) and 2.24 eV (SrScCuS3) from the diffuse reflectance spectra. The latter value is in good agreement with that calculated by the DFT method. The narrower band gap of EuScCuS3 is explained by the presence of 4f-5d transition in Eu2+ ion that indicates a possibility to control the band gap of the chalcogenides by the inclusion of Eu. The activation energy of crystal structure defects, being the source of additional absorption in the NIR spectral range, was found to be 0.29 eV.
Сomplex study of the crystal structure and properties of quaternary compounds AScCuS3 (A = Sr, Eu). Display omitted
•The AScCuS3 (A = Sr, Eu) compounds are mid-gap, indirect-bandgap semiconductors.•The EuScCuS3 compound exhibits ferromagnetic properties at low temperature, and SrScCuS3 is a diamagnetic.•The compound EuScCuS3 is more stable in the inert atmosphere than SrScCuS3, and both melt incongruently.•The ab initio calculations of the Raman and infrared spectra of AScCuS3 (A = Sr, Eu) agree well with experiment.
We present the results of investigations of the spin-polarized current and spin dynamics in the hybrid structures ferrimagnetic insulator/ferromagnetic metal subjected to microwave radiation. We ...studied the La0.7Sr0.3MnO3/Y3Fe5O12 bilayer films on the Gd3Ga5O12 substrate. It was experimentally established that under the action of spin pumping the resistance of the La0.7Sr0.3MnO3 film changes. The value of ΔR is maximum in the sample with a La0.7Sr0.3MnO3 layer thickness of 10 nm and sharply drops as the manganite film thickness is increased. The resistance decreases in the paramagnetic region and grows in the ferromagnetic region at temperatures below the metal-insulator transition point. The variation in the resistance of the manganite film can be attributed to the correlation of the spin dynamics and transport properties of conduction electrons in the structure.
The growth and phase formation features, along with the influence of structure and morphology on the electronic, optical, and transport properties of Cr2GeC and Cr2-xMnxGeC MAX phase thin films ...synthesized by magnetron sputtering technique, were studied. It was found that the Cr:Ge:C atomic ratios most likely play the main role in the formation of a thin film of the MAX phase. A slight excess of carbon and manganese doping significantly improved the phase composition of the films. Cr2GeC films with a thicknesses exceeding 40 nm consisted of crystallites with well-developed facets, exhibiting metallic optical and transport properties. The hopping conduction observed in the Cr2-xMnxGeC film could be attributed to the columnar form of crystallites. Calculations based on a two-band model indicated high carrier concentrations N, P and mobility μ in the best-synthesized Cr2GeC film, suggesting transport properties close to single crystal material. The findings of this study can be utilized to enhance the growth technology of MAX phase thin films.
The growth and phase formation features, along with the influence of structure and morphology on the electronic, optical, and transport properties of Crsub.2GeC and Crsub.2-xMnsub.xGeC MAX phase thin ...films synthesized by magnetron sputtering technique, were studied. It was found that the Cr:Ge:C atomic ratios most likely play the main role in the formation of a thin film of the MAX phase. A slight excess of carbon and manganese doping significantly improved the phase composition of the films. Crsub.2GeC films with a thicknesses exceeding 40 nm consisted of crystallites with well-developed facets, exhibiting metallic optical and transport properties. The hopping conduction observed in the Crsub.2-xMnsub.xGeC film could be attributed to the columnar form of crystallites. Calculations based on a two-band model indicated high carrier concentrations N, P and mobility μ in the best-synthesized Crsub.2GeC film, suggesting transport properties close to single crystal material. The findings of this study can be utilized to enhance the growth technology of MAX phase thin films.
The negative magnetoresistance of thin In2O3 films, obtained by an autowave oxidation reaction, was detected within a temperature range of 4.2–80K. The magnetoresistance was –1.35% at a temperature ...of 4.2K and an external magnetic field of 1T. A weak localization theory was used to explain the negative magnetoresistance and to determine the phase-coherence length in a temperature range of 4.2–80K. The phase-coherence length was found to oscillate as the temperatures increased to around 30K. From the maximum and minimum values of the oscillation of the phase-coherence length, it was suggested that the In2O3 film has two structure characteristic parameters. Transmission electron microscopy showed the structure of the thin In2O3 film to have structural features of a «crystal phase – amorphous phase». It was found that the crystalline phase characteristic size was consistent with the maximum phase-coherence length and the amorphous phase characteristic size was consistent with the minimum phase-coherence length. It has been suggested that the temperature measurements of the magnetoresistance and the theory of weak localization can be used to evaluate the structural features of nanocomposite or nanostructured thin films.
•The magnetoresistance of the thin In2O3 film was −1.35% at a temperature 4.2K.•Negative magnetoresistance has been explained by the weak localization theory.•The temperature dependence of phase-coherence length lϕ began to oscillate at 30K.•The oscillation of lϕ can be used to evaluate the structural features of thin films.
Three-layer iron-rich Fe
Si
/Ge/Fe
Si
(0.2 <
< 0.64) heterostructures on a Si(111) surface with Ge thicknesses of 4 nm and 7 nm were grown by molecular beam epitaxy. Systematic studies of the ...structural and morphological properties of the synthesized samples have shown that an increase in the Ge thickness causes a prolonged atomic diffusion through the interfaces, which significantly increases the lattice misfits in the Ge/Fe
Si
heterosystem due to the incorporation of Ge atoms into the Fe
Si
bottom layer. The resultant lowering of the total free energy caused by the development of the surface roughness results in a transition from an epitaxial to a polycrystalline growth of the upper Fe
Si
. The average lattice distortion and residual stress of the upper Fe
Si
were determined by electron diffraction and theoretical calculations to be equivalent to 0.2 GPa for the upper epitaxial layer with a volume misfit of -0.63% compared with a undistorted counterpart. The volume misfit follows the resultant interatomic misfit of |0.42|% with the bottom Ge layer, independently determined by atomic force microscopy. The variation in structural order and morphology significantly changes the magnetic properties of the upper Fe
Si
layer and leads to a subtle effect on the transport properties of the Ge layer. Both hysteresis loops and FMR spectra differ for the structures with 4 nm and 7 nm Ge layers. The FMR spectra exhibit two distinct absorption lines corresponding to two layers of ferromagnetic Fe
Si
films. At the same time, a third FMR line appears in the sample with the thicker Ge. The angular dependences of the resonance field of the FMR spectra measured in the plane of the film have a pronounced easy-axis type anisotropy, as well as an anisotropy corresponding to the cubic crystal symmetry of Fe
Si
, which implies the epitaxial orientation relationship of Fe
Si
(111)0-11 || Ge(111)1-10 || Fe
Si
(111)0-11 || Si(111)1-10. Calculated from ferromagnetic resonance (FMR) data saturation magnetization exceeds 1000 kA/m. The temperature dependence of the electrical resistivity of a Ge layer with thicknesses of 4 nm and 7 nm is of semiconducting type, which is, however, determined by different transport mechanisms.
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