LaAg x In1−x

The structures of LaAg _x In_1–x alloys withx=0.75, 0.89 are determined by neutron diffraction on powder samples. The space group isI4/mmm (D _4h ^/17 ). The lattice constants splitting, the order parameter and the mean square vibrational amplitudes of the atoms are given in the temperature range from 20 KT300 K.     

Negatron effects in CdSe1 − x Te x and ZnS1−x Se x films

Various negatron effects in films of alloys of II–VI compounds deposited from solutions as a function of the deposition mode and heat treatment are studied. It is found that the negative photocapacitance effect, which was first discovered in ZnS_1?x Se _x films, and the slowly relaxing negative photoelectric effects, which are caused by the transition of electrons located in a nanoscale surface layer from the shallow energy levels of trapping centers to deeper levels with a lower polarizability and by the presence of nanoscale clusters in these materials, which play the role of a “reservoir” for minority charge carriers, occur according to a single mechanism. A model to explain the basic laws of negative photoconductivity in CdSe_{1 ? x} Te _x films deposited from a solution is proposed. Negative residual conductivity is explained in terms of double-barrier relief model, while negative differential photoconductivity is attributed to the presence of nanoscale electric domains.     

Formation of Ti1–x Si x and Ti1–x Si x N films by magnetron co-sputtering

The paper reports on surface morphology, structure and microhardness of TiSi–N films formed by cosputtering from two target-facing unbalanced magnetrons, equipped with pure Ti and Si targets, on an unheated substrate rotating in front of both targets. The ratio Si/Ti in the TiSi–N film was achieved by modifying the magnitude of currents in the individual magnetrons and by the addition of nitrogen to the film. The rotation of the substrate has a strong effect on the film deposition rate and its morphology. The deposition rate is 3 times lower than that of the film deposited on a stationary substrate. The surface roughness of a polycrystalline Ti film deposited on the rotating substrate is considerably higher than that on a stationary substrate. On the contrary, the surface of an amorphous Si film is smooth and there is no difference between the roughness of Si films sputtered on stationary and on rotating substrates. The hardness of the film increases with increasing Si content and with the addition of nitrogen to the TiSi film. The Ti(26 at.%)Si(8.5 at.%)N(65 at.%)-film sputtered on an unheated rotating steel substrate, held at a floating potential, exhibited the best result with a hardness of 29 GPa.     

Magnetic Parameters of Hg1–x Mn x Se1–y S y and Hg1–x Mn x Te1–y S y Crystals

The magnetic susceptibility of Hg_1–x Mn _x Se_1–y S _y and Hg_1–x Mn _x Te_1–y S _y crystals is investigated by the Faraday method at H = 3 kOe in the temperature interval T = 77–300 K. It is established that the specific features of are due to Mn–S–Mn–S, Mn–Se–Mn–Se, and Mn–Te–Mn–Te clusters and mixed Mn–Se–Mn–S and Mn–Te–Mn–S clusters of different sizes in which the indirect exchange antiferromagnetic interaction between Mn atoms is realized through chalcogen atoms. Based on the dependences 1/_Mn = f(T), the magnetic parameters are determined and their dependences on the crystal composition (x and y) are established.     

Oxidation of Si(100)2x1 and Gex Si1−x (100)2x1

High resolution electron energy loss Spectroscopy (HREELS), X-ray photoelectron Spectroscopy (XPS) and low energy electron diffraction (LEED) have been used to characterize initial stages of oxidation of Si(100)2x1 and Ge_x Si_1−x (100)2x1 surfaces. Different oxidation stages of Si were identified by measuring Si 2p core level shifts and characteristic vibrations of Si-O-Si complexes. The latter may be described in the framework of continuous random network models.Then,from the experimentally determined frequencies, force constants,average bond angles and bond lengths are determined. Complementary,marker experiments with atomic hydrogen as a probe in conjunction with HREELS were used to determine the local, atomic structure for different stages of oxidation from chemical shifts of Si-H and Ge-H stretching mode intensities, respectively.     

Specific heat of Eu x Sr1−x Te

In this paper, we report on measurements of the specific heatC of single-crystalline Eu _x Sr_1–x Te at temperatures between 60 mK and 15 K and in magnetic fields up to 6 T. Pure antiferromagnetic EuTe shows unusual critical behavior in the vicinity of the Néel temperatureT _N=9.8 K with a positive critical exponent instead of the 3d-Heisenberg exponent =–0.12. Possible reasons for this discrepancy between theory and experiment include magnetic anisotropy effects due to magnetic dipole-dipole interactions, which may give rise to a cross-over of the critical behavior very close toT _N. This anisotropy is also seen in the specific heat below 1 K where an exponential decay ofC is observed, and in the dependence of the magnetic susceptibility on the direction of the applied field. With increasing dilution of EuTe with nonmagnetic Sr, the critical behavior changes: becomes negative and decreases continuously towards –1 atxx _c. This concentration dependence of was previously observed in the diluted ferromagnetic system Eu _x Sr_1–x S. Our data thus support that the apparent change in the critical behavior depends on the degree of disorder. Samples with concentrationx lower than the critical concentrationx _c reveal spin-glass behavior in the specific heat. In addition, the dependence ofT _N on magnetic fields is discussed. The data yield a normalized magnetic phase boundaryB _c(T)/B_c(T=0) vs.T _N(B)/T_N(B=0) which is independent of concentration.     

On the magnetic susceptibility of Pd1−x Ag x in the range 0.5≦x≦1

The weak variation of the magnetic bulk susceptibility of Pd_1–x Ag _x with temperature T and silver mole fractionx within 0.5x1 has been investigated in the range 5KT400K. Experimental evidence can be given for an intersection point of the susceptibility isotherms (T=const,x) atx=0.55. The observed dependence of on T andx is interpreted by means of a semiphenomenological alloy susceptibility function (T,x).     

Spin-wave resonance in [Co x Ni1 − x ]N and [Co x P1 − x ]N gradient films

Gradient films of ferromagnetic 3d metals with prescribed magnetic potential profile along the film thickness are obtained. It is found that the spin-wave resonance spectrum in these films is characterized by anomalous dependences of resonance fields of spin-wave modes H _r on the mode number: H _r(n) ～ n, H _r(n) ～ n ^2/3.     

The crystallization of Fe1−x P x , 0.09≦x≦0.26

The crystallization behaviour of about 60 samples of electrodeposited Fe_1–x P _x , 0.09<x<0.26, was investigated with DSC and X-ray diffraction. Several subsequenting transformations during heating at 10 K/min were identified. The corresponding transformation temperatures, reaction heats and reaction rates were measured. If the as-deposited samples contain metal-rich crystallites (microcrystalline and partly amorphous material) crystallization starts with primary precipitation of -iron followed by polymorphous crystallization of Fe₃P. In amorphous samples these two processes become less important compared with the eutectoid reaction the higher the phosphorus content. In a small concentration range around 19 at% P this transformation is the only one. Above this range the primary crystallization of Fe₃P becomes more and more dominant.     

Pb1−x Fe x films prepared by vapor condensation

ZF, LF and TF SR experiments with antiferromagnetic (AF) ceramical samples La_2–x Sr _x CuO_4–y have been performed in the temperature range 10–300 K. Zero field muon spin polarization functions obtained below the Neel temperature clearly show a nonzero initial precession phase-–0.35 rad. We propose an explanation based on existence of the dynamical magnetic fields on the muon.We thank Drs. A.G. Chistov and A.M. Brjazkalo from RSC Kurchatov Institute for the preparation the #2 La₂CuO_4–y sample.     

High-Moment-Low-Moment Description of Magnetovolume Effects in Y(Mn x Al 1− x ) 2 and Y x Sc 1− x Mn 2

Based on the assumption of a high-moment-low-moment instability of the Mn atom, we construct a simple spin model with coupled magnetic and spatial degrees of freedom to describe the Laves phase systems Y(Mn x Al 1 m x ) 2 and Y x Sc 1 m x Mn 2 . Monte Carlo simulations of this model qualitatively reproduce anomalies observed in these materials like a discontinuous giant volume change and anomalous thermal expansion behavior.     

Magnetotransport effects in paramagnetic Gd x Mn1 − x S

The electrical resistance of Gd _x Mn_{1 ? x} S solid solutions with x = 0.1, 0.15, and 0.2 has been measured at magnetic field H = 0.8 T and at zero magnetic field within the 100 K < T < 550 K temperature range. The magnetoresistance peak is observed above room temperature. On heating, the composition with x = 0.2 exhibits the change of magnetoresistance sign from positive to negative and the magnetoresistance peak near the transition to the magnetically ordered state. The experimental data are interpreted in the framework of the model involving the orbital ordering of electrons and the arising electrical polarization leading to the changes in the spectral density of states for electrons in the vicinity of the chemical potential in the applied magnetic field.     

Lattice dynamics of ZnSe x S1 − x semiconductor crystals

Recently ultrabroadband infrared solid state lasers based on a new vibronic material Cr²⁺:ZnSe _x S_1–x were demonstrated [1–3]. Cr²⁺ ion substitutes the metal ion (tetrahedral sites), the crystal field of the solid solution is responsible for large inhomogeneous broadening of Cr²⁺ electron states. The crystal field can be reconstructed by investigation of lattice dynamics — optical phonon parameters and dielectric function in IR. We paid special attention to investigation of vibrational and infrared spectroscopic properties of ZnSe _x S_{1 ? x} crystals. A very interesting and somewhat unexpected result of these studies was the existence in the crystals of effective S-Se dipoles, which generate an additional deep dynamically charged level in the forbidden gap of the semiconductors. The results of the first-principles calculations of both the phonon structure and the electron localization in ZnSe _x S_1–x crystals as well as acceptor levels in Cr²⁺: ZnSe crystal are discussed.     

Martensitic transformation in La1−x Yb x Ag1−y In y

The structural phase transformation of La_1–x Yb _x Ag_1–y In _y has been studied on single crystals by low temperature Laue-technique. The martensitic transformation in this pseudobinary intermetallic alloy has to be characterized as a weak orthorhtombic distortion of a single I centered unit cell (c/a1.04;a/b1.006) and a collective slipping or twinning of these cells that gives a fixed orientation between the remaining cubic room temperature structure and the martensitic phase. Above room temperature exists an order-disorder transformation from the CsCl-B2 structure to an at room temperature metastable W-A2 structure. There is no dramatic change in the physical properties of this alloy by substituting La by Yb, so we may approximate our results to LaAg_1–y In _y .This paper is dedicated to Prof. Dr. S. Methfessel on the occasion of his 60^th birthday     

Mechanism of charge transfer in injection photodiodes based on the In-n +-CdS-n-CdS x Te1 − x -p-Zn x Cd1 − x Te-Mo structure

Photosensitive In-n ⁺-CdS-n-CdS _x Te_{1 ? x} -p-Zn _x Cd_{1 ? x} Te-Mo film structures based on II–VI semiconductors and operating in the wavelength range λ = 0.490–0.855 μm have been fabricated. These structures in the forward current direction at high bias voltages operate as injection photodiodes and exhibit a high integrated sensitivity S _int ≈ 700 A/lm (14500 A/W) at room temperature. It has been found that, in the fabricated structures at low illuminance levels and low forward bias voltages (0.05–0.50 V), the diffusion and drift fluxes of nonequilibrium charge carriers are directed toward each other. This effect leads to the sign reversal of the photocurrent, which makes it possible on the basis of these structures to create selective photodetectors with injection properties. In the reverse direction of the photocurrent, these structures also operate in the mode of internal amplification of the primary photocurrent, but the integrated sensitivity in this mode is considerably less than that in the forward current direction.     

High-temperature ferromagnetism in Si1 ? x Mn x (x ≈ 0.5) nonstoichiometric alloys

It has been found that the Curie temperature (T _C ?? 300 K) in nonstoichiometric Si_{1 ? x} Mn _x alloys slightly enriched in Mn (x ?? 0.52?C0.55) in comparison to the stoichiometric manganese monosilicide MnSi becomes about an order of magnitude higher than that in MnSi (T _C ?? 30 K). Deviations from stoichiometry lead to a drastic decrease in the density of charge carries (holes), whereas their mobility at about 100 K becomes an order of magnitude higher than the value characteristic of MnSi. The high-temperature ferromagnetism is ascribed to the formation of defects with the localized magnetic moments and by their indirect exchange interaction mediated by the paramagnetic fluctuations of the hole spin density. The existence of defects with the localized magnetic moments in Si_{1 ? x} Mn _x alloys with x ?? 0.52?C0.55 is supported by the results of numerical calculations performed within the framework of the local-density-functional approximation. The increase in the hole mobility in the nonstoichiometric material is attributed to the decay of the Kondo (or spin-polaron) resonances presumably existing in MnSi.     

Mössbauer spectroscopic study of FeAl1−x Co x

We report the results of a Mössbauer study of the alloy sytem FeAl_1?x Co _x forx ≥ 0.3 at temperatures down to 83 K. Magnetic splitting is observed forx ≥ 0.35 at all temperatures. However, forx=0.3, no splitting is observed at room temperature, and superparamagnetic behavior occurs at LN₂ temperature. The magnetically split spectra are fitted each with a distribution of hyperfine fields and the average hyperfine field \(\bar B_{hf} \) as a function of temperature is obtained. The variation of \(\bar B_{hf} \) withT is explained using the model of magnetic clusters with collective magnetic excitations from which the saturation hyperfine field and the magnetic anisotropy energy for these clusters are obtained. Also, the results are discussed using the model of random atomic distributions, and the agreement between the calculated and the experimentally obtained distributions of hyperfine fields is found improve asx increases.     

Cathodoluminescence spectra of Cd1−x Zn x Te solid solutions

An investigation is made of the cathodoluminescence, electrical properties, and structural features of crystals of Cd_1−xZn_xTe solid solutions with composition x ranging from 0.02 to 0.20 mole fraction as compared with CdTe and ZnTe. The main bands of the cathodoluminescence spectra are identified within the range 500–2700 nm. The role of oxygen in Cd_1−xZn_xTe cathodoluminescence is shown. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 96–100, January–February, 2000.     

The superconducting transition temperature of Pb1−x Mn x films

Results of the superconducting transition temperatureT _c of amorphous and microcrystalline films of lead doped with manganese as magnetic impurity are reported in this work. The amorphous films show an Abrikosov-Gor'kov behaviour, whereas for the crystalline films there is a much smaller depression and a peak for higher Mn concentrations, which indicates a region of coexistence of superconductivity and magnetic ordering as a spinglass.Supported by the Deutsche Forschungsgemeinschaft in the Sonderforschungsbereich 125, Fehlordnung in Metallen — Aachen, Jülich, Köln