We report the giant magnetoimpedance effect in a ferromagnetic metal/insulator/semiconductor (MIS) diode with the Schottky barrier based on the Fe/SiO2/n-Si structure. It was established that the ...applied magnetic field strongly influences the impedance of the structure in the temperature range 10—30 K. In this range, there is the pronounced peak in the temperature dependence of the real part of the impedance at frequencies from 10 Hz to 1 MHz. The effect of the magnetic field manifests itself as a shift of the peak of the real part of the impedance. Under the action of a bias voltage of 5 V, the peak of the real part of the impedance similarly shifts toward lower temperatures with and without applied magnetic field.
We have investigated the properties of a several bioelectrodes based on the immobilization of Gluconobacter oxydans bacterial cells on carbon superfine materials (CFMs). We use three types of CFMs ...(as adopted by the working classification CFM 1-3). All bioelectrodes was formed by covering the surface of the CFM via suspension of bacteria in a chitosan gel. The properties of samples are evaluated by measuring the physiological state of the bacteria immobilized: (a) recording the intensity of cellular respiration, (b) for measuring the charge transport characteristics of electrode (bioelectrocatalysis), and (c) by measuring the electrode impedance. Measurements (b) and (c) are made on two and three-electrode circuits in the oxidation of ethanol in the presence of 2,6-dichlorophenol electron transport mediator. For CFMs 1 and 2 the electron transport by the oxidation of the substrate is not registered, while for CFM 3 the current generation occurs. The resistance of CFM 3 bioelectrode is below the resistance of CFMs 1 and 2 both before (39.6 kΩ/cm2 for CFM 3, 630 Ω/cm2 for CFM 2, and 1329 Ω/cm2 for CFM 1) and after the addition of the substrate (2.9 kΩ/cm2 for CFM 3, 45 kΩ/cm2 for CFM 2, and 58 kΩ/cm2 for CFM 1). The bioelectrode made of CFM 3 has a capacitance of 196 μF/cm2-greater than two orders of magnitude of the bioelectrode capacity of CFMs 1 and 2 (0.51 and 0.58 μF/cm2, respectively). It is important to further study the properties of the CFM class of materials, which are promising as the basis of mechanically flexible electrodes with controlled parameters.
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•Nanoscale vertical heterostructures based on graphene and 2D VTe2 were proposed.•Calculated TMR ratio for the favorable threelayer heterostructure is 220%.•T-VTe2 monolayer in ...bilayer T-VTe2/graphene is 100% spin-polarized.•The hole doping of graphene and the exchange splitting of the Dirac cone is revealed.
New perspective 1.4 nm thick spin-polarized triple heterostructures based on graphene sandwiched between two vanadium ditelluride monolayers (VTe2/graphene/VTe2) were studied using ab initio DFT technique. Both possible trigonal prismatic (H-VTe2) and octahedral (T-VTe2) VTe2 phases were considered to design and study graphene-based heterostructures. It was shown that the interaction with graphene changes the electronic structure of 2D T-VTe2 from metallic to half-metallic, making T phase perspective to be used for magnetic tunnel junctions. The electronic subsystem of graphene fragment is slightly hole doped. Calculated tunnel magnetoresistance ratio for the favorable heterostructure configuration estimated within the Julliere model is 220%, which opens a way to use VTe2/graphene/VTe2 as prospective magnetic tunnel junction in novel spintronic nanodevices based on tunnel magnetic resistance and spin transfer torque effects.
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.
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.
Using Density Functional Theory and Periodic Boundary Conditions it is shown that the hydroxylated/oxygenated/halogenated Mn2C monolayer is a 2D ferromagnetic material with a local Mn ions magnetic ...moment of 2.7μв per unit cell. Upon oxygenation the ferromagnetic coupling between Mn ions can be transformed into a superposition of magnetic states. In particular, the intrinsic magnetic moments in the hydroxylated/halogenated Mn2C monolayer can attain up to 6μB per unit cell. It is found that oxygen termination induces flat bands in the band structure, which evidence for the strong electron correlations and could lead to the implementation of exotic quantum phases in 2D crystals and high-temperature superconductivity. Along with the potential of the hydroxylated Mn2C monolayer characterized by the half-metallicity for application in spintronic devices as a perfect spin injector/detector, this material like other conventional MXenes is promising for the use in energy storage, electromagnetic interference shielding, and sensing.
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•Hydroxylated/oxygenated/halogenated Mn2C monolayers are a 2D ferromagnetic materials.•Mn2C surface passivation by F and Cl ions yields the maximum magnetic moments up to 5.63 μB.•Hydroxylated Mn2C monolayer characterized by 100% spin polarization.
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.
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 use of spintronic devices with a tunable magnetic order on small scales is highly important for novel applications. The MAX phases containing transition metals and/or magnetic ion-substituted ...lattices attract a lot of attention. In this study, the magnetic and electronic properties of (Crsub.4-x Fesub.x )sub.0.5 AC (A = Ge, Si, Al) compounds were predicted and investigated within the density functional theory. It was established that single-substituted (Crsub.3 Fesub.1 )sub.0.5 AC (A = Ge, Si, Al) lattices are favorable in terms of energy. An analysis of the magnetic states of the MAX phases demonstrated that their spin order changes upon substitution of iron atoms for chromium ones. It was found that mostly the (Crsub.4-x Fesub.x )sub.0.5 GeC and (Crsub.4-x Fesub.x )sub.0.5 AlC lattices acquire a ferrimagnetic state in contrast to (Crsub.4-x Fesub.x )sub.0.5 SiC for which the ferromagnetic spin order dominates. It was pointed out that the atomic substitution could be an efficient way to tune the magnetic properties of proposed (Crsub.4-x Fesub.x )sub.0.5 AC (A = Ge, Si, Al) MAX phases.
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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