M. V. Sapozhnikov

Using laser sputtering to obtain semiconductor nanoheterostructures

Laser sputtering of solid-state targets in a hydrogen atmosphere has been used to form semiconductor nanoheterostructures. Impurities (Te or Mn) in the form of delta-doped layers obtained by laser sputtering of the corresponding targets in the process of vapor-phase epitaxy using organometallic compounds can be introduced into light-emitting structures based on the InGaAs/GaAs system to make it possible to control the spectrum and the electroluminescence intensity. Reducing the hydrogen pressure in the reactor to 25-50Torr allows laser deposition to be carried out at reduced temperatures of the epitaxial layers of the base material and makes it possible to obtain GaAs and InAs semiconductors with a high manganese-doping level that demonstrate ferromagnetic properties at room temperature.

Inhomogeneous states and the mechanism of magnetization reversal of a chain of classical dipoles

The inhomogeneous states (solitons) in a single chain of classical dipoles are studied numerically and analytically. An analytical solution to the problem is based on the long-wave approximation for dipole sums which holds for high magnetic fields perpendicular to the dipole chain. The analytical and numerical solutions are in reasonable agreement. The magnetization reversal is investigated by numerical simulation based on the Landau-Lifshitz stochastic equations. It is demonstrated that the magnetization reversal of a dipole chain at a finite temperature has a thermal activation nature and occurs through the formation of a stable phase nucleus (a soliton at the edge of the chain) and its growth (the motion of the soliton along the chain).

Magnetic and optical properties of nanocorrugated Co films

Nanostructured Co films were prepared on the top of a polymethyl methacrylate (PMMA) colloidal crystals by magnetron sputtering. Optical reflectance spectra were studied in the range of near UV, IR, and visible light for p- and s-polarizations. Valleys were observed in the spectra and their positions scaled with the PMMA sphere diameter. Both the surface plasmon resonance and the dipole resonance of single Co nanocaps should be considered to explain the obtained results. Magneto-optic measurements showed the qualitative change of the magnetization curve and the enhancement of magneto-optic rotation at wavelength λ=632 nm in comparison with the control Co film.

Ferromagnetism in epitaxial germanium and silicon layers supersaturated with managanese and iron impurities

The possibility of laser synthesis of diluted magnetic semiconductors based on germanium and silicon doped with manganese or iron up to 10–15 at % has been shown. According to data on the electronic levels of 3d atoms in semiconductors, Mn and Fe impurities are most preferable for realizing ferromagnetism in Ge and Si through the Ruderman-Kittel-Kasuya-Yosida mechanism. Epitaxial Ge and Si layers 50–110 nm in thickness were grown on gallium arsenide or sapphire single crystal substrates heated to 200–480°C. The content of a 3d impurity has been measured by x-ray spectroscopy. The ferromagnetism of layers and high magnetic and acceptor activities of Mn in Ge, as well as of Mn and Fe in Si, are manifested in the observation of the Kerr effect, anomalous Hall effect, high hole conductivity, and anisotropic ferromagnetic resonance at 77–500 K. According to the ferromagnetic resonance data, the Curie point of Ge:Mn and Si:Mn on a GaAs substrate and of Si:Fe on an Al2O3 substrate is no lower than 420, 500, and 77 K, respectively.

Effect of compressive and tensile stresses in GaMnAs layers on their magnetic properties

The effect of elastic stresses (compressive, tensile) on the magnetic properties of epitaxial GaMnAs layers prepared by laser deposition of solid-state targets in a gas atmosphere on different buffer sublayers (InxGa1 − xAs and InxGa1 − xP) and substrates (GaAs, InP) has been investigated. It has been established from the investigations of magnetic-field dependences of the Hall resistance that all layers exhibit ferromagnetic properties with the Curie temperature ∼50 K. It has been shown that, in the case of tensile stresses in GaMnAs layers (InxGa1 − xAs and InxGa1 − xP buffers and InP substrate), the anomalous Hall effect shape demonstrates a predominant orientation of the easy-magnetization axis in the growth direction, unlike the GaMnAs layers prepared on a GaAs substrate (with compressive stresses), which demonstrate the predominance of the component of the magnetization vector in the layer plane.

Ferromagnets based on diamond-like semiconductors GaSb, InSb, Ge, and Si supersaturated with manganese or iron impurities during laser-plasma deposition

Properties of thin (30–100 nm) layers of diluted magnetic semiconductors based on diamond-like compounds III–V (InSb and GaSb) and elemental semiconductors Ge and Si doped with 3d impurities of manganese and iron up to 15% were measured and discussed. The layers were grown by laser-plasma deposition onto heated single-crystal gallium arsenide or sapphire substrates. The ferromagnetism of layers with the Curie temperature up to 500 K appeared in observations of the ferromagnetic resonance, anomalous Hall effect, and magneto-optic Kerr effect. The carrier mobility of diluted magnetic semiconductors is a hundred times larger than that of the previously known highest temperature magnetic semiconductors, i.e., copper and chromium chalcogenides. The difference between changes in the magnetization with temperature in diluted semiconductors based on III–V, Ge, and Si was discussed. A complex structure of the ferromagnetic resonance spectrum in Si:Mn/GaAs was observed. The results of magnetic-force microscopy showed a weak correlation between the surface relief and magnetic inhomogeneity, which suggests that the ferromagnetism is caused by the 3d-impurity solid solution, rather than ferromagnetic phase inclusions.

Effect of ferromagnetic nanoparticles on the transport properties of a GaMnAs microbridge

A chain of Co nanoparticles was formed along a GaMnAs microbridge by electron beam lithography. The magnetic state of the particles was manipulated by a magnetic force microscope probe. It was found that resistance of the microbridge depended on the state of the particles and was different for the particles in the single-domain and vortex states. The resistance exhibited steplike behavior in an external magnetic field. This behavior was the result of the effect of the inhomogeneous stray fields of the particles on the microbridge resistance. The observed phenomenon can be used as an alternative way to control GaMnAs transport properties.

Nonreciprocal light diffraction by a lattice of magnetic vortices

We report on experimental study of optical properties of two-dimensional square lattice of triangle Co and CoFe nanoparticles with a vortex magnetization distribution. We demonstrate that intensity of light scattered in diffraction maxima depends on the vorticity of the particles magnetization and it can be manipulated by applying an external magnetic field. The experimental results can be understood in terms of phenomenological theory.

A (Ga, Mn)Sb magnetic semiconductor for spintronic applications

The structural, optical, and galvanomagnetic properties of (Ga, Mn)Sb layers grown by the laser sputtering of solid targets in H2 flow are n studied. It is shown that at a growth temperature of 400°C, (Ga, Mn)Sb layers are single-crystal up to high Mn concentrations. The magnetic field dependence of the Hall resistance at measuring temperatures of 10–300 K contains a hysteresis loop; i. e., the layers are ferromagnetic semiconductors.

Influence of the microcrystalline structure on the magnetic properties of ferromagnetic films and structures on their base

This paper presents the results of investigating the crystal structure of thin films of the Co40Fe60 composition obtained by magnetron sputtering on their magnetic properties and properties of ferromagnetic nanostructures formed from these films using the optical and electron lithography. It has been found experimentally that magnetic properties of the structures depend on the crystalline-grain sizes, which can be controlled by means of deposition of additional buffer layers of various materials ∼1 nm thick on the substrate under the ferromagnetic film. It has been shown that the crystallite size can be the main factor that determines the minimal lateral sizes of the structures with specified magnetic properties, which are formed from thin ferromagnetic films.