S. N. Varnakov

Study of the structural and magnetic characteristics of epitaxial Fe3Si/Si(111) films

The results of the structural and magnetic studies of the epitaxial structure prepared during the simultaneous evaporation from two iron and silicon sources on an atomically pure Si(111)7 × 7 surface at a substrate temperature of 150°C have been presented. The epitaxial structure has been identified as a single-crystal Fe3Si silicide film with the orientation Si[111]‖Fe3Si[111] using methods of the X-ray structural analysis, transmission electron microscopy, and reflection high-energy electron diffraction. It has been established that the epitaxial Fe3Si film at room temperature has magnetic uniaxial anisotropy (Ha = 26 Oe) and a relatively narrow uniform ferromagnetic resonance line (ΔH = 11.57 Oe) measured at a pump frequency of 2.274 GHz.

Analysis of optical and magnetooptical spectra of Fe5Si3 and Fe3Si magnetic silicides using spectral magnetoellipsometry

The optical, magnetooptical, and magnetic properties of polycrystalline (Fe5Si3/SiO2/Si(100)) and epitaxial Fe3Si/Si(111) films are investigated by spectral magnetoellipsometry. The dispersion of the complex refractive index of Fe5Si3 is measured using multiangle spectral ellipsometry in the range of 250–1000 nm. The dispersion of complex Voigt magnetooptical parameters Q is determined for Fe5Si3 and Fe3Si in the range of 1.6–4.9 eV. The spectral dependence of magnetic circular dichroism for both silicides has revealed a series of resonance peaks. The energies of the detected peaks correspond to interband electron transitions for spin-polarized densities of electron states (DOS) calculated from first principles for bulk Fe5Si3 and Fe3Si crystals.

Solid-State Reactions in Fe/Si Multilayer Nanofilms

Solid-state reaction processes in Fe/Si multilayer nanofilms have been studied in situ by the methods of transmission electron microscopy and electron diffraction in the process of heating from room temperature up to 900ºС at a heating rate of 8-10ºС/min. The solid-state reaction between the nanolayers of iron and silicon has been established to begin at 350-450ºС increasing with the thickness of the iron layer.

Optical characteristics of an epitaxial Fe3Si/Si(111) iron silicide film

The dispersion of the relative permittivity ɛ of a 27-nm-thick epitaxial Fe3Si iron silicide film has been measured within the E = 1.16–4.96 eV energy range using the spectroscopic ellipsometry technique. The experimental data are compared to the relative permittivity calculated in the framework of the density functional theory using the GGA-PBE approximation. For Fe3Si, the electronic structure and the electronic density of states (DOS) are calculated. The analysis of the frequencies corresponding to the transitions between the DOS peaks demonstrates qualitative agreement with the measured absorption peaks. The analysis of the single wavelength laser ellipsometry data obtained in the course of the film growth demonstrates that a continuous layer of Fe3Si iron silicide film is formed if the film thickness achieves 5 nm.

FEATURES OF THE ELLIPSOMETRIC INVESTIGATION OF MAGNETIC NANOSTRUCTURES

The technique for interpreting magneto-ellipsometric measurements is proposed. The model of a homogeneous semi-infinite medium for reflecting layered magnetic structures in the presence of the magnetic field in the configuration of the magneto-optical equatorial Kerr effect is considered. Based on the analysis of the Fresnel coefficients with regard to the magneto-optical parameter Q appearing in the off-diagonal elements of the permittivity tensor, the expressions are obtained using which the refraction (n) and absorption (k) coefficients, the real (Q1) and imaginary (Q2) parts of the magneto-optical parameter can be found from the ellipsometric (ψ0 and Δ0) and magneto-ellipsometric (ψ0 + δψ and Δ0 + δΔ) measurements. The results will allow to measure and analyze the magnetic characteristics such as hysteresis loops and the coercitive force of layered nanostructures using the conventional ellipsometric equipment.

Analysis of the structure and magnetic properties of an interface in multilayered (Fe/Si)N nanostructures with the surface-sensitive XMCD method

The structural and magnetic properties of (Fe/Si)N nanostructures obtained by successive deposition on the SiO2/Si(100) surface at a temperature of the substrate of 300 K have been studied. The thicknesses of all Fe and Si layers have been determined by transmission electron microscopy measurements. The magnetic properties have been studied by the X-ray magnetic circular dichroism (XMCD) method near the Fe L3, 2 absorption edges. The orbital (ml) and spin (mS) contributions to the total magnetic moment of iron have been separated. The thicknesses of magnetic and nonmagnetic iron silicide on the Si/Fe and Fe/Si interfaces have been determined with the surface sensitivity of the XMCD method and the model of the interface between the nonmagnetic and weakened magnetic phases.

Iron silicide-based ferromagnetic metal/semiconductor nanostructures

Ferromagnetic single-crystal epitaxial Fe3Si films and polycrystalline Fe5Si3 films are obtained on Si substrates by molecular-beam epitaxy with in situ control of the structure, optical, and magnetic properties. The results of the structural, magnetic, and optical measurements are discussed. The experimental data are compared to the results of the microscopic calculation of the spin-polarized structure, the permittivity, and the optical conductivity spectra.

Selective synthesis of higher manganese silicides: a new Mn 17 Si 30 phase, its electronic, transport, and optical properties in comparison with Mn 4 Si 7

The electronic structure, transport and optical properties of thin films of Mn4Si7 and Mn17Si30 higher manganese silicides (HMS) with the Nowotny “chimney-ladder” crystal structure are investigated using different experimental techniques and density functional theory calculations. Formation of new Mn17Si30 compound through selective solid-state reaction synthesis proposed and its crystal structure is reported for the first time, the latter belonging to I-42d. Absorption measurements show that both materials demonstrate direct interband transitions around 0.9xa0eV, while the lowest indirect transitions are observed close to 0.4xa0eV. According to ab initio calculations, ideally structured Mn17Si30 is a degenerate n-type semiconductor; however, the Hall measurements on the both investigated materials reveal their p-type conductivity and degenerate nature. Such a shift of the Fermi level is attributed to introduction of silicon vacancies in accordance with our DFT calculations and optical characteristics in low photon energy range (0.076–0.4xa0eV). The Hall mobility for Mn17Si30 thin film was found to be 25xa0cm2/Vxa0s at Txa0=xa077xa0K, being the highest among all HMS known before. X-ray photoelectron spectroscopy discloses a presence of plasmon satellites in the Mn4Si7 and Mn17Si30 valence band spectra. Experimental permittivity spectra for the Mn4Si7 and Mn17Si30 compounds in a wide range (0.076–6.54xa0eV) also indicate degenerate nature of both materials and put more emphasis upon the intrinsic relationship between lattice defects and optical properties.

Ellipsometric technique for determining in situ the absorption coefficient of semiconducting nanolayers

An algorithm that makes it possible to solve the inverse problem of ellipsometry aimed at determining the absorption coefficient on the basis of a single-zone ellipsometric experiment during the growth of thin semiconducting films is developed and implemented. The technique is based on analysis of the variation of ellipsometric parameters Ψ and Δ directly during the growth. The algorithm is tested in synthesis of Si/SiO2/Si(100) and Hg1 − xCdxTe structures.