Anomalous ferromagnetic resonance in manganese- and aluminum-doped germanium layers deposited from the laser plasma

Ferromagnetic resonance (FMR) with an anomalous angular dependence has been observed in the Ge:(Mn, Al)/GaAs nanolayers deposited from laser plasma at a reduced temperature of 150°C. The resonance is associated with the needle-like inclusions of a high-temperature ferromagnetic phase with the Curie temperature T _C > 293 K. Such a magnetic anisotropy is confirmed by the atomicforce and magneticforce microscopy of a side chip. A low-temperature ferromagnetic phase with normal FMR and T _C < 212 K is formed between the needle-like inclusions. This phase manifests itself in the anomalous Hall effect at 77 K and probably is a solid solution of manganese in germanium.     

Nanosize layers of silicon and manganese ferromagnetic alloys deposited from laser plasma

The results of studying random silicon-manganese alloys with Mn concentration increased up to 50 at % and discrete alloys (multilayer structures with silicon and manganese layers 5–20 and 1–5 nm thick, respectively) deposited from laser plasma are presented. Structure and composition were checked by atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and Auger electron spectroscopy. In Si-Mn discrete alloys, the high-level hole conduction with the conventional linear Hall effect was observed. For silicon-manganese random alloy layers with Mn concentration increased up to 50 at %, the hysteresis abnormal Hall effect, magnetooptic Kerr effect and anisotropic dependence between the microwave absorption and magnetic field typical for plane ferromagnets were recorded up to 293 K. Ferromagnetism of homogeneously doped silicon layers is due not to the separation of the second phase with the excess of Mn but with the unusual properties of silicon and manganese alloys prepared in heavily nonequilibrium conditions. Structural measurements of discrete alloys confirmed the presence of the periodic depth distribution of silicon and manganese. The first data about the character of atom mixing near the layer boundaries during the laser synthesis were obtained. Results obtained by applied mathematical and statistical analysis of the sequences of separate photoelectron lines observed during the Si-Mn system ion profiling in depth were given.     

The special features of the Hall effect in GaMnSb layers deposited from a laser plasma

Epitaxial GaMnSb films with Mn contents up to about 10 at. % were obtained by deposition from a laser plasma in vacuum. The growth temperature T _s during deposition was varied from 440 to 200°C, which changed the concentration of holes from 3 × 10¹⁹ to 5 × 10²⁰ cm^?3, respectively. Structure studies showed that, apart from Mn ions substituting Ga, the GaMnSb layers contained ferromagnetic clusters with Mn and shallow acceptor defects of the Ga_Sb type controlled by the T _s value. Unlike single-phase GaMnSb systems studied earlier with negative anomalous Hall effect values and Curie temperatures not exceeding 30 K, the films obtained in this work exhibited a positive anomalous Hall effect, whose hysteresis character manifested itself up to room temperature and was the more substantial the higher the concentration of holes. The unusual behavior of this effect was interpreted in terms of the interaction of charge carriers with ferromagnetic clusters, which was to a substantial extent determined by the presence of Schottky barriers at the boundary between the clusters and the semiconducting matrix; this interaction increased as the concentration of holes grew. The absence of this effect in semiconducting compounds based on III–V Group elements with MnSb or MnAs ferromagnetic clusters was discussed in the literature; we showed that this absence was most likely related to the low hole concentrations in these objects.     

Nonlinearity and hysteresis in longitudinal current transport in CoSi/GaAs alloy layers deposited from laser plasma

The electron transport properties of nanosized CoSi alloy layers deposited at a lowered temperature (350°C) from laser plasma onto single-crystalline gallium arsenide have been studied. An asymmetry of the current-voltage characteristic (CVC) in the longitudinal current transport in such layers has been found, which indicates the spin polarization of charge carriers, and a substantial (up to 18%) nonlinearity and a hysteresis (up to 4%) have been revealed both at room temperature and at 77 K for comparatively low current densities (up to 5 × 10⁴ A/cm²). In repeated cycles of CVC measurements at 77 K, irreversible changes in the properties of the layers have been observed.     

Optical and magneto-optical properties of room-temperature ferromagnetic In(Ga)MnAs layers, deposited by pulse laser ablation

Spectral dependences of refractive and absorption indices n(hν), k(hν) (hν=1.2-4.4 eV) and the transversal Kerr effect δ(hν) (hν=0.5-4.4 eV) in In(Ga)MnAs layers fabricated by laser deposition have been investigated. Spectra of the diagonal and off-diagonal components of the dielectric permittivity tensor of these layers have been calculated. Comparison of the spectral dependences δ(hν), ε′(hν) and ε′₂×(hν)² of the In(Ga)MnAs layers with similar spectra for MnAs has been carried out. Particular features in the spectra of the In(Ga)MnAs layers have been explained by a competition of contributions of the In_1−x(Ga_1−x)Mn_xAs host and MnAs inclusions.     

Laser-plasma deposited nanosized layers of ferromagnetic semiconductors and silicon- and germanium-based Heusler alloys

The electric, magnetic resonance, and magneto-optical properties of thin laser-plasma deposited 50–100-nm layers of diluted magnetic semiconductors Ge:(Mn, Al)/GaAs, Ge:(Mn, Al)/Si, and Heusler alloys Co₂MnSi/Si, Co₂MnSi/GaAs, and Fe₂CrSi/GaAs with T _c > 293 K were studied. Anomalous ferromagnetic resonance in Ge:(Mn, Al) layers, ferromagnetism in CoSi/Si characterized by strong hysteresis in the magneto-optic Kerr effect, and the anomalous Hall effect at 293 K were observed.     

Luminescence from compressed electron-hole plasma in germanium

We have studied the luminescence spectra from compressed electron-hole plasma in pure germanium. The spectra show a satisfactory thermalization of the charge carriers and lead to a reasonable value of the compressibility. These features encourage to further experimental efforts in the studies of the Mott transition in highly excited semiconductors.     

Anomalous behavior of the surface state in ferromagnetic superconductors

The effect of the electromagnetic interaction between the persistent current and the magnetic moments to the surface state in ferromagnetic superconductors is studied theoretically. This interaction causes an oscillatory decay of the penetrated magnetic field near the magnetic phase transition temperature. Below a critical temperature, the spontaneous surface magnetization is stabilized by the magnetic field induced by the surface persistent current.     

Magnetism in structures with ferromagnetic and superconducting layers

The influence of superconductivity on ferromagnetism in the layered Ta/V/Fe_1–x V _x /V/Fe_1–x V _x /Nb/Si structures consisting of ferromagnetic and superconducting layers is studied using polarized neutron reflection and scattering. It is experimentally shown that magnetic structures with linear sizes from 5 nm to 30 μm are formed in these layered structures at low temperatures. The magnetization of the magnetic structures is suppressed by superconductivity at temperatures below the superconducting transition temperatures in the V and Nb layers. The magnetic states of the structures are shown to undergo relaxation over a wide magnetic-field range, which is caused by changes in the states of clusters, domains, and Abrikosov vortices.     

Anomalous interaction of a plasma flow with the boundary layers of a geomagnetic trap

Using the data from the Interball-1, GEOTAIL, THEMIS and CLUSTER satellites, we propose a mechanism of anomalous magnetosheath dynamics. This mechanism yields that plasma boundaries can be locally deformed over distances comparable to its thickness. In particular, the magnetospheric boundary, the magnetopause, is deformed over distances up to a few Earth radii (R _E) under the pressure of supermagnetosonic plasma streams (SPSs), instead of reacting to plasma pressure decreases, as it was previously thought. Supermagnetosonic plasma streams having a kinetic pressure a few times larger than the solar wind pressure and the magnetic pressure behind the magnetopause, can crush the magnetopause and even push it outside the mean bow shock position, as determined through the average pressures balance. Anomalous magnetosheath dynamics is initiated by plasma flow anomalies (FAs), triggered by rotational discontinuities, by jumps in the solar wind pressure and by interplanetary shocks, which all interact with the bow shock. We show that the generation mechanism for SPSs, adjacent to the FA, is connected with the compensation of the FA flow reduction by the SPS enhanced flow, which is produced by polarization electric fields at the FA edges. Statistically, SPSs are extreme events, relayed with intermittency and multifractality inside the boundary layers of the geomagnetic trap. In this way, SPSs provide “long-range” interactions between global and microscales. A similar role may be played by fast concentrated flows in the geomagnetic tail, in fusion devices, in astrophysical plasmas and in hydrodynamics.     

Tailoring the photoluminescence of PbS-nanoparticles layers deposited by means of the pulsed laser ablation technique

In this article, we report on the room-temperature pulsed laser deposition (PLD) of lead sulfide (PbS) nanoparticles (NPs) layers onto various substrates. It is particularly shown that the average size of PbS NPs can be controlled by varying the number of laser ablation pulses. The pulsed laser deposited PbS NPs are found to be of high-crystalline quality and their photoluminescence (PL) to blue shift significantly from 1420 to 880 nm, as their average diameter is decreased from 8.5 to 2.5 nm, thereby confirming the quantum size effect. The latitude of our PLD process is shown to permit the achievement of multilayered PbS-NPs structures of which the overall PL emission spectrum can be tailored through the appropriate stack of individual PbS-NPs layers.     

Anomalous Hall effect in ferromagnetic semiconductors in the hopping transport regime

We present a theory of the anomalous Hall effect in ferromagnetic (Ga,Mn)As in the regime when conduction is due to phonon-assisted hopping of holes between localized states in the impurity band. We show that the microscopic origin of the anomalous Hall conductivity in this system can be attributed to a phase that a hole gains when hopping around closed-loop paths in the presence of spin-orbit interactions and background magnetization of the localized Mn moments. Mapping the problem to a random resistor network, we derive an analytic expression for the macroscopic anomalous Hall conductivity sigma(AH)(xy). We show that sigma(AH)(xy) is proportional to the first derivative of the density of states varrho(epsilon) and thus can be expected to change sign as a function of impurity band filling. We also show that sigma(AH)(xy) depends on temperature as the longitudinal conductivity sigma(xx) within logarithmic accuracy.     

Anomalous Hall effect and electron transport in ferromagnetic MnBi films

The electron transport properties of highly c-axis oriented MnBi thin films of various thicknesses have been investigated. Samples are metallic but the low temperature resistivity shows an unusual T(3) dependence. Transverse Hall effect measurements show that both the ordinary and anomalous Hall coefficients decrease with decreasing temperature below 300 K, but the ordinary Hall coefficient (R(0)) undergoes a sign reversal around 105 K, where the magnetic anisotropy also changes sign. Analysis of the Hall data for various samples shows that the anomalous Hall coefficient (R(s)) exhibits a strong ρ(2) dependence, where ρ is the longitudinal resistivity.     

Domain width from ferromagnetic resonance in single crystal nickel films

Two resonances have been observed during ferromagnetic resonance measurements on strained single crystal nickel films at 132 K and at a microwave frequency 17 GHz. The lower field line can be interpreted as due to a multidomain structure. Multidomain analysis gives a value of the domain width, w = 1.6 ± 0.1 × 10^-5 cm, which is in agreement with the result from a different method.     

About the blue satellites to the resonance lines in laser produced plasma

Air breakdown is produced at low laser intensity by keeping a metallic target at the focus of the converging lens. Blue satellite is observed to the resonance line of first ionization state of nitrogen atom. The cause of the blue satellite and its variation with laser intensity is discussed.     

On the spin-wave resonance in bulk ferromagnetic conductors

The shape of the absorption curve of ferromagnetic experimental permeability is found and relations are derived for the resonance line width, the magnitude of the resonance field and the correction of the g-factor for the spin-wave resonance of ferromagnetic conductors for an arbitrary value of the surface anisotropy. The relations are used to discuss the results of the measurements and to show the dominant role of the skin-effect in the ferromagnetic resonance of bulk monocrystalline conductors with a small number of defects.