Single-layer vanadium nitride (VN) and bilayer Pd
0.96
Fe
0.04
/VN and VN/Pd
0.92
Fe
0.08
thin-film heterostructures for possible spintronics applications were synthesized on (001)-oriented ...single-crystalline magnesium oxide (MgO) substrates utilizing a four-chamber ultrahigh vacuum deposition and analysis system. The VN layers were reactively magnetron sputtered from a metallic vanadium target in Ar/N
2
plasma, while the Pd
1−
x
Fe
x
layers were deposited by co-evaporation of metallic Pd and Fe pellets from calibrated effusion cells in a molecular beam epitaxy chamber. The VN stoichiometry and Pd
1−
x
Fe
x
composition were controlled by X-ray photoelectron spectroscopy. In situ low-energy electron diffraction and ex situ X-ray diffraction show that the 30 nm thick single-layer VN as well as the double-layer VN(30 nm)/Pd
0.92
Fe
0.08
(12 nm) and Pd
0.96
Fe
0.04
(20 nm)/VN(30 nm) structures have grown cube-on-cube epitaxially. Electric resistance measurements demonstrate a metallic-type temperature dependence for the VN film with a small residual resistivity of 9 μΩ·cm at 10 K, indicating high purity and structural quality of the film. The transition to the superconducting state was observed at 7.7 K for the VN film, at 7.2 K for the Pd
0.96
Fe
0.04
/VN structure and at 6.1 K for the VN/Pd
0.92
Fe
0.08
structure with the critical temperature decreasing due to the proximity effect. Contrary to expectations, all transitions were very sharp with the width ranging from 25 mK for the VN film to 50 mK for the VN/Pd
0.92
Fe
0.08
structure. We propose epitaxial single-crystalline thin films of VN and heteroepitaxial Pd
1−
x
Fe
x
/VN and VN/Pd
1−
x
Fe
x
(
x
≤ 0.08) structures grown on MgO(001) as the materials of a choice for the improvement of superconducting magnetic random access memory characteristics.
Anion doping of tungsten trioxide by nitrogen is used to obtain electrochrome cathode materials, the spectral transmittance of which can be controlled by the doping level. A series of samples was ...synthesized by reactive magnetron sputtering of a metal tungsten target in a mixture of argon, nitrogen, and oxygen gases, the flow rate of the latter was varied at a constant pressure of the gas mixture. Warm-colored tungsten oxynitride films were prepared at higher doping levels with their morphology and elemental composition characterized using scanning electron microscopy, crystal structure described using X-ray diffraction and the valence state of constituents revealed with X-ray photoelectron spectroscopy techniques. Optical properties were measured by making use of transmission spectrophotometry and spectroscopic ellipsometry. These extensive experimental studies revealed an increase in absorption towards shorter wavelengths below the wavelength of 0.5 µm with an increase in the doping level. At the same time, it was found that with an increase in the doping level, partial reduction of the tungsten occurs, and the fraction of non-stoichiometric oxygen steadily increases to half of the total oxygen content. It is a common belief that the imperfection of the doped material facilitates the intercalation of the material by electrolyte ions.
A series of Pd1-xFex alloy epitaxial films (x = 0. 0.038. 0.062. and 0.080). a material promising for superconducting spintronics, was prepared and studied with ultrafast optical and magneto-optical ...laser spectroscopy in a wide temperature range of 4-300 K. It was found that the transition to the ferromagnetic state causes a qualitative change of both the reflectivity and the magneto-optical Kerr effect transients. A nanoscale magnetic inhomogeneity of the ferromagnet/paramagnet type inherent in the palladium-rich Pd1-xFex alloys reveals itself through the occurrence of a relatively slow. 10-25 ps. photoinduced demagnetization component following a subpicosecond one; the former vanishes at low temperatures only in the x = 0.080 sample. We argue that the 10 ps timescale demagnetization originates most probably from the diffusive transport of d electrons under the condition of nanoscale magnetic inhomogeneities. The low-temperature fraction of the residual paramagnetic phase can be deduced from the magnitude of the slow reflectivity relaxation component. It is estimated as ≈30% for x = 0.038 and ≈15% for x = 0.062 films. The minimal iron content ensuring the magnetic homogeneity of the ferromagnetic state in the Pd1-xFex alloy at low temperatures is about 7-8 atom %.
We have investigated the low-temperature magnetoresistive properties of a thin epitaxial Pd0.92Fe0.08 film at different directions of the current and the applied magnetic field. The obtained ...experimental results are well described within an assumption of a singledomain magnetic state of the film. In a wide range of the appled field directions, the magnetization reversal proceeds in two steps via the intermediate easy axis. An epitaxial heterostructure of two magnetically separated ferromagnetic layers. Pd0.92Fe0.08/Ag/ Pd0.96Fe0.04. was synthesized and studied with de magnetometry. Its magnetic configuration diagram has been constructed and the conditions have been determined for a controllable switching between stable parallel, orthogonal, and antiparallel arrangements of magnetic moments of the layers.
Magnetic nanoparticles embedded into semiconductors have current perspectives for use in semiconducting spintronics. In this work, 40 keV Fe+ ions were implanted in high fluences of (0.5 ÷ 1.5) × ...1017 ion/cm2 into an oxide semiconductor and single-crystalline TiO2 plates of rutile structure with (100) or (001) face orientations. Microstructure, elemental-phase composition, and magnetic properties of the Fe-ion-implanted TiO2 were studied by scanning and transmission electron microscopies (SEM and TEM), X-ray photoelectron (XPS) and Rutherford backscattering (RBS) spectroscopies, as well as vibrating-sample magnetometry (VSM). The high-fluence ion implantation results in the formation of magnetic nanoparticles of metallic iron beneath the irradiated surface of rutile. The induced ferromagnetism and observed two- or four-fold magnetic anisotropy are associated with the endotaxial growth of Fe nanoparticles oriented along the crystallographic axes of TiO2.
Thin epitaxial films of the palladium-rich Pd
1−
x
Fe
x
alloy were synthesized and extensively studied as a tunable ferromagnetic material for superconducting spintronics. The (001)-oriented MgO ...single-crystal substrate and the composition range of
x
= 0.01–0.07 were chosen to support the epitaxial growth and provide the films with magnetic properties spanning from very soft ferromagnet for memory applications to intermediately soft and moderately hard for the programmable logic and circuit biasing, respectively. Dependences of the saturation magnetization, Curie temperature and three magnetic anisotropy constants on the iron content
x
were obtained for the first time from the analyses of the magnetometry and ferromagnetic resonance data. The experimental results were discussed based on existing theories of dilute ferromagnetic alloys. Simulation of the hysteresis loops within the Stoner-Wohlfarth model indicates the predominant coherent magnetic moment rotation at cryogenic temperatures. The obtained results were compiled in a database of magnetic properties of a palladium-iron alloy in a single-crystal thin-film form considered as a material for superconducting spintronics.
In nanoscale layered S/F1/N/F2/AF heterostructures, the generation of a long-range, odd-in-frequency spin-projection one triplet component of superconductivity, arising at non-collinear alignment of ...the magnetizations of F1 and F2, exhausts the singlet state. This yields the possibility of a global minimum of the superconducting transition temperature T c, i.e., a superconducting triplet spin-valve effect, around mutually perpendicular alignment.
The superconducting triplet spin valve is realized with S = Nb a singlet superconductor, F1 = Cu41Ni59 and F2 = Co ferromagnetic metals, AF = CoO x an antiferromagnetic oxide, and N = nc-Nb a normal conducting (nc) non-magnetic metal, which serves to decouple F1 and F2. The non-collinear alignment of the magnetizations is obtained by applying an external magnetic field parallel to the layers of the heterostructure and exploiting the intrinsic perpendicular easy-axis of the magnetization of the Cu41Ni59 thin film in conjunction with the exchange bias between CoO x and Co. The magnetic configurations are confirmed by superconducting quantum interference device (SQUID) magnetic moment measurements. The triplet spin-valve effect has been investigated for different layer thicknesses, d F1, of F1 and was found to decay with increasing d F1. The data is described by an empirical model and, moreover, by calculations using the microscopic theory.
The long-range triplet component of superconducting pairing is generated from the singlet component mainly at the N/F2 interface, where the amplitude of the singlet component is suppressed exponentially with increasing distance d F1. The decay length of the empirical model is found to be comparable to twice the electron mean free path of F1 and, thus, to the decay length of the singlet component in F1. Moreover, the obtained data is in qualitative agreement with the microscopic theory, which, however, predicts a (not investigated) breakdown of the triplet spin-valve effect for d F1 smaller than 0.3 to 0.4 times the magnetic coherence length, ξF1.
Single‐crystalline Fe1+xTe iron telluride with off‐stoichiometric iron has been synthesized by the Bridgman method. The X‐ray diffraction and wave‐length‐dispersive X‐ray electron‐probe microanalysis ...characterization have shown Fe1.125Te stoichiometry of the samples. Spin‐polarized ab initio calculations of the electric field gradients around interstitial iron atoms for Fe1.125Te have shown that in the first and second coordination rings around interstitial iron, the spin and electron densities are strongly perturbed against the stoichiometric ones. Together with the interstitial iron this gives rise to three kinds of iron centers making up a round‐corner plaquette. The room‐temperature Mössbauer spectra measured at different incidence angles of gamma‐radiation are satisfactorily fitted utilizing the hyperfine parameters, calculated within the plaquette model. The low‐temperature data are well described with the assumption of an incommensurate collinear spin density wave (SDW) phase, showing consistency with neutron scattering data for the Fe1.125Te system.
Binary FeTe should exhibit superconductivity according to ab initio calculations, but it does not. Different from the computational model, real samples are always non‐stoichiometric (Fe1+xTe). The combined ab initio calculations and Mössbauer spectroscopy of Fe1.125Te reveal two kinds of iron centers forming a plaquette around the interstitial iron ion. This creates a specific magnetic background on which the superconductivity issue should be re‐considered.
A thin‐film styrene polymer–carbon nanoparticle composite was obtained in a single‐stage alternating current dielectric barrier discharge plasma‐chemical process. The allotropic forms of the carbon ...nanoparticle filler were traced by transmission electron microscopy (TEM). TEM revealed an extraordinary adhesive encapsulation of the carbon nanoparticles by the polymer. It was found that the corona discharge regime provides an onion‐like carbon filler that enhances the mechanical strength and chemical resistance of the synthesized polymer–carbon nanoparticle film. Measurements of the electrical properties of the films implicitly confirmed the uniformity of the carbon filler distribution.
Alternating current dielectric barrier discharge plasma allows production of styrene polymer coatings uniformly filled with carbon nanoparticles. This single‐stage synthesized armored coating demonstrates enhanced mechanical strength and resistance against a conventional solvent. Transmission electron microscopy studies show carbon nanoparticles firmly encapsulated by the polymer.
The FeTe parent compound for iron‐superconductor chalcogenides was studied applying Mössbauer spectroscopy accompanied by ab initio calculations of electric field gradients at the iron nuclei. ...Room‐temperature (RT) Mössbauer spectra of single crystals have shown asymmetric doublet structure commonly ascribed to contributions of over‐stoichiometric iron or impurity phases. Low‐temperature Mössbauer spectra of the magnetically ordered compound could be well described by four hyperfine‐split sextets, although no other foreign phases different from Fe1.05Te were detected by XRD and microanalysis within the sensitivity limits of the equipment. Density functional ab initio calculations have shown that over‐stoichiometric iron atoms significantly affect electron charge and spin density up to the second coordination sphere of the iron sub‐lattice, and, as a result, four non‐equivalent groups of iron atoms are formed by their local environment. The resulting four‐group model consistently describes the angular dependence of the single crystals Mössbauer spectra as well as intensity asymmetry of the doublet absorption lines in powdered samples at RT. We suppose that our approach could be extended to the entire class of Fe1+ySe1−xTex compounds, which contain excess iron atoms.
Fe1.05 Te parent compound for iron superconductor chalcogenides was studied with Mössbauer spectroscopy from room to liquid helium temperatures. Density functional ab initio calculations of electric field gradients revealed four non‐equivalent groups of iron atoms formed by their different local environment. The four‐group model consistently explains angular dependence of the Mössbauer spectra in single crystals as well as intensity asymmetry of the doublet absorption lines in powder samples at RT.
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