The Hall effect in PdSi based amorphous alloys containing Co

The Hall effect in amorphous Pd_80–x Si₂₀Co _x , wherex=8, 9, 10, 12, 15, 20 (at.% are implied throughout) alloys was investigated. The measurements were carried out at r.t. in fields up to 17·5 kGauss. The variation of the Hall fieldE _H vs magnetic fieldB shows features typical for bulk ferromagnetics. The Hall constantR ₁ describing the extraordinary effect ranges from 0·29 to 27·64 (×10^–/4 in cm³/A. sec both) reaching its maximum value for the alloy withx= =12. The interpretation of theE _H vsB curves obtained is based on a model with magnetic clusters carrying giant magnetic moments. These clusters are considered to have close relation to the clusters observed by electron microscopy. Magnetic moment of an average magnetic cluster is estimated to be of the order of 1000 _B for the alloys with more than 9 at.% Co.     

Hall effect of noncrystalline Zr−Cu films

Quench condensed Zr _x Cu_1–x films offer a wide concentration range (0.1x0.9) for measurements of the Hall coefficientR _H of amorphous Zr–Cu alloys.R _H changes sign as a function of composition, from negative to positive, as the Zr concentration is increased. The sign change is observed in a narrow concentration range at aboutx=0.22, without any peculiarity of the conductivity at this crossover concentration. The Hall coefficient of the unannealed Zr-rich films is nearly independent of temperature. However, both, the values ofR _H and of the temperature dependence ofR _H change with a heat treatment well below the crystallization temperature. This is most obvious for the films with a composition close to the cross-over concentration.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday     

Elastic constants of the alloys Cd1−x Zn x (x<0.3%) and their temperature dependence

The temperature dependence of elastic constants of Cd_1–x Zn _x alloys, havingx=0.021, 0·042 and 0·233 at.%, has been measured in the temperature range from 4·2 to 300 K by the pulse-echo-overlap ultrasonic method. The adiabatic compressibilities and the Debye temperatures have been calculated. All elastic constants with the exception ofc ₄₄ increase slightly with the growing concentration of Zn.The summary of this paper was presented on the 7^th Conference on Ultrasonic Methods in ilina, September 11^th–13^th, 1980.     

On the magnetic susceptibility of the liquid Pd1−x Si x alloy system at 1825 K

The isothermal magnetic susceptibility (x) of the completely miscible liquid Pd_1–x Si _x alloy system shows a rapid monotonous decrease withx from strong paramagnetism to weaklyx-dependent diamagnetism. The measured susceptibility isotherm at 1825 K is analysed within 0x1 by using a semiphenomenological method of decomposing the magnetic susceptibility into its constituent parts. Because of the empirical similarity between liquid and glassy metals this interpretation also provides assertions about the magnetism of glassy Pd_1–x Si _x aroundx=0.2.     

Positron annihilation studies on the electronic structure of Pd−Ag−H system

Angular Correlation of Annihilation Radiation (ACAR) is shown to be useful to examine the electronic structure of -phase Pd_1–y Ag _y H _x system. Hydrogen absorption by Pd_1–y Ag _y alloys results in the increase of both nearly free andd-localized electron numbers in compliance with the KKR-CPA calculation outcomes. The investigation of -phase systems, PdH _x hydrides as well as Pd_1–y Ag _y H _x materials, failed because of a high concentration of lattice defects.     

Electronic transport properties of amorphous NiTi alloys

Measurements of electrical resistivity, magnetoresistance and Hall effect on amorphous Ni_100–x Ti _x alloys withx=39, 43, 60, 65, 70, and 76 are presented. The resistivity at 4.2 K is in the range 210 cm to 325 cm. The Hall coefficient turns out to be negative for low Ti contents and positive for high Ti contents with values around –6×10^–11 m³/As and +7×10^–11 m³/As, respectively. At low temperatures, the temperature and magnetic field dependences of the quantities measured are analysed and discussed in terms of weak localisation and electron-electron interaction effects.     

Scattering of conduction electrons by vacancies in aluminium

The low-field Hall coefficientR _H ⁰ and transverse magnetoresistance /₀ were measured in high-purity polycrystalline aluminium samples which were quenched from temperatures between 350 and 500°C. The measurements were made at 4.2 K in magnetic fields up to 40 kG. It was found that the low-field Hall coefficientR _H ⁰ of aluminium containing vacancies lies between –1.0 and –2.5×10^–5 cm³ A^–1s^–1, which is in good agreement with the calculation of Pfändner, Böning and Brening.     

119Sn-mössbauer,IR, and DSC study of tin oxyfluoride glasses

The¹¹⁹Sn-Mössbauer spectra ofxSnO·(70–x)SnF₂·30P₂O₅ glasses (0 x70) measured at 78 K comprised a doublet due to Sn²⁺ (=3.30–3.36 mm s^–1, = 1.70–1.72 mm s^–1) and a weak singlet due to Sn⁴⁺ located at –0.23 mm s^–1 with respect to BaSnO₃. The and of Sn²⁺ were comparable to those of Sn₂P₂O₇. Small Debye temperatures (146 and 155 K) were obtained from the low-temperature measurements. These results indicate that Sn²⁺ and Sn₄₊ occupied interstitial sites, being loosely and ionically bonded to distorted PO_4–x F _x tetrahedra.     

Heavy-fermion behavior and spin-glass freezing in Si-stabilized amorphous alloys based on UPt3

U-Pt-Si and U-(Pt, Pd)-Si alloys have been prepared in the amorphous state by splat-cooling. The average nearest-neighbor distance is the same as the U-Pt distance in UPt₃. The low-temperature behavior of these alloys (with composition (U_0.25Pt_0.75)_1–xSi_x, x=0.18, 0.20, 0.25; and (U_0.25(Pt_1–yPd_y)_{0.75 0.8}Si_0.2,y=0.05 and 0.1) has been studied by specific heatC, magnetization and resistivity measurements in the temperature range 1.5 K to 20 K and for magnetic fields up to 6 T. Some samples were investigated down to 0.1 K and the specific heat for one sample was measured in fields up to 22 T. With ₀ =C/T| _T0 between 0.25 and 0.35 J/moleUK², the alloys can be classified as heavy-fermion materials. As opposed to UPt₃, the alloys exhibit spin-glass behavior with a concomitant decrease of ₀. The magnetization exhibits typical spin-glass features (e.g., an irreversibility line). An inverse relationship between ₀ andT _max (temperature ofC/T maximum which is proportional to the spin-glass freezing temperature), irrespective of the Pd content, is observed. The behavior can be qualitatively described by a coexistence of heavy-fermion behavior and spin-glass freezing.     

Magnetostriction characteristics of the iron rich Fe-B-Si metallic glasses

Linear longitudinal and transverse magnetostriction and forced volume magnetostriction curves versus magnetic field for some as-quenched iron-rich amorphous alloys are presented. For the Fe₇₈Si₈B₁₄, Fe₇₈Si₉B₁₃ and Fe₇₉Si₁₂B₉ alloys the linear saturation magnetostriction was equal to 37·6×10^–6, 28·9×10^–8 and 34×10^–6, respectively.This work was in part financially supported by the Warsaw Technical University Institute of Material Science and Technology within the framework of the Project CPBR 2·4.     

Potential of Si1−xGex alloys for Auger generation in highly efficient solar cells

Recent investigation on Si solar cells demonstrated the utility of Auger generation for the creation of more than merely one electron/hole pair per absorbed photon. The semiconductor Si requires a minimum photon energy of about 3.4 eV for this internal carrier multiplication. The current of a Si cell is therefore not significantly increased by Auger generation when the cell is illuminated by an air mass 1.5 spectrum, which contains only few photons with energies above 3.4 eV. Use of Si_1–x Ge _x alloys promises a lower onset energy. Unfortunately, incomplete data on band structures ofrandom Si_1–x Ge _x alloys preclude a detailed quantitative discussion of the full potential for these materials. Nevertheless, (i) analogies to our own quantum efficiency data from pure Si, (ii) the calculated band structure of the hypothetical,ordered zincblende type Si_0.5Ge_0.5 crystal, and (iii) optical data for Si_1–x Ge _x alloys indicate an optimum Ge content ofx=0.6 tox=0.7.     

Supertransferred hyperfine interaction in magnetic insulators (II)

The important mechanisms of supertransferred hyperfine (STHF) interactions in N–O–M chains are briefly discussed: (i) spin polarization ofns states in the N-ion due to the s-d exchange interaction,H _STHF ^sd ; (ii) contributions of spin-polarized states of the intervening O-ion,H _STHF ^II ; (iii) transfer of d-electrons of the M-ion to emptyns states in the N-ion,H _STHF ^III . The dependence ofH _STHF upon the N–O–M bond configuration, electronic structure, and orbital state of the M-ion is presented in a convenient form. The STHF interactions in the chains Sn⁴⁺–O^2––Fe³⁺, Cr³⁺ in compounds with slightly distorted Perovskite structure are considered. The STHF field in the chain Sn⁴⁺–O^2––Cr³⁺ is shown to change the sign within the range of angles near 170°. This conclusion is in line with published data on the isoelectronic chain Sn⁴⁺–O²–Mn⁴⁺ in the compounds Ca_1–x Sr _x MnO₃. The results obtained for the N–O–Fe³⁺ chain are rationalized by the predicted angular dependence ofH _STHF=+ cos + cos². Features of the STHF interactions in N–O–M chains with an M-ion in an orbital degenerate state are examplified by a preliminary analysis of N–O^2––V³⁺ chains in orthovanadites.     

The theory of neutron scattering from mixed harmonic solids

In the intermediate valent cerium alloys Ce_1–xY_xPd₃, Ce(Pd_1–xRh_x)₃ and Ce(Pd_1–xAg_x)₃ the Gd³⁺-ESR shows a non-linear increase of the linewidth H(T) in the temperature range 4.2KT300K. The deviation from the linear Korringa law can be described by a reduced conduction electron density of states at the Gd site (which is a Ce lattice site) in the energy range E _4f (=width of the Ce 4f states). This supposition allows a determination of E _4f from the H(T)-data. For CePd₃:Gd³⁺ we find E _4f=(650±100) K. E _4f increases with Y- and Rh-concentration and decreases with Ag-concentration.     

Nuclear orientation study of the decay of204BiFe

The decay of²⁰⁴Bi nuclei (I =6⁺, T_1/2=11·22 h) oriented in an iron host was investigated on the JINR low-temperature nuclear orientation facility SPIN. The orientation parameterB ₂=1·17 (6) was obtained from the analysis of six prominent E1 gamma-transitions. From the measured normalized intensities of the gamma-rays observed some 70 values of multipole mixing ratios for the gamma-transitions in²⁰⁴Pb nucleus were determined for the first time. The spins 6, 6, 5 and 4 could be uniquely assigned to the²⁰⁴Pb negative parity levels at 3891·5 keV, 3768·4 keV, 3301·5 keV and 2338·2 keV, respectively. The spin-parity assignments of the levels at 4183·8 keV, 4094·2 keV, 3782·0 keV, 2506·9 keV and 2065·1 keV were confirmed as 6^–, 6^–, 5^–, 5^– and 5⁺, respectively. For the level at 3105·1 keV spin-parity 5^– was suggested and spinparity 7^– of the level at 2696·4 keV was called in question. The possible placements of the gammatransitions 3 1351·7 keV and 1353·4 keV in the decay scheme is discussed. The reorientation parameters for the long-living levels at 2264·2 keV (T _1/2=0·45 s) and 1273·9 keV (T _1/2= =265 ns) were determined asG ₂=0·41 (14) andG ₂=0·60 (17), respectively. For the isomeric level at 2185·7 keV (T _1/2=67·2 min) the value ofG ₂=0·88 (49) was proposed.The authors would like to express their thanks to T. I. Kracíková and M. Trhlík for the valuable discussions in the course of the evaluation of the experimental data.     

The d-resonance scattering in amorphous Fe x Pd80−x Si20 alloy

The electrical resistivity of amorphous Fe _x Pd_80–x Si₂₀ alloy has been discussed in terms of extended Ziman theory. The increase in the electrical resistivity of Fe _x Pd_80–x Si₂₀ has been predicted due to the d-resonance scattering of the conduction electrons by Fe-atoms.Dedicated to Academician Vladimír Hajko on the occasion of his 65th birthday.     

Electrical resistivity and thermoelectric power of amorphous niobium-nickel alloys synthetized by vapour quenching

Thin film samples (10–20 thick) of niobium-nickel alloys in the composition range Nb-5 to 95 at % Ni were vapour quenched by R. F. sputtering onto fused quartz substrates held at a temperature of 450 K. It was found that fully glassy alloys were synthetized in the composition range Nb-30 to 85 at % Ni, 2·5 times larger than reported for splat-quenched alloys. Crystallization temperatures exhibited maxima near the eutectic composition and are comparable to those of splat-quenched materials. At room temperature, the electrical resistivity of these alloys lies between 176–210 cm, and the absolute thermoelectric power S between 2·20–2·52 V/K. On increasing the temperature from 4·2 to 775 K, up to which the amorphous alloys are stable, the resistivity of the alloy with=0·50 decreases by about 1·5%; the value of d/dT progressively increases with increasing Ni content, becoming positive at 0·50dS/dT of all alloys lies between 6–8·5×10^–3V deg^–2. The electrical behaviour of these alloys may be treated in terms of electron scattering in disordered structures assuming the nearly free-electron model, in a manner analogous to Ziman's theory of electronic transport in liquid metals.     

Correlation betweenJ c and screw dislocation density in sputtered YBa2Cu3O7-δ films

Electric transport properties of sputtered YBa₂Cu₃O_7– films were studied as a function of screw dislocation density, ranging from 5·10⁷ cm^–2 to 1.3·10⁹ cm^–2 as determined at the film surface. A correlation was found between the number of screw dislocations and the critical current density (J _c ). Films with higher screw dislocation densities have higher critical current densities and a slower drop ofJ _c as a function of applied magnetic fieldH.     

Some physical properties of calcia and yttria stabilized ThO2 ceramics

In this paper the density, electrical conductivity, and dielectric permittivity of vacant ceramics of Ca _x Th_1–x O_2–x and Y _x Th_1–x O_2–x /2 type, respectivelly, were investigated as functions of temperature, frequency, and composition of these systems.The density drops with increasing calcium or yttrium amount, respectively. In the ThO₂-CaO system this is in agreement with the mechanism of formation of vacant phase Ca _x Th_1–x O_2x . The decrease of porosity in the ThO₂-Y₂O₃ system with increasing yttrium content can be due various factors which influence the mobility of Y³⁺ ions and, thus, also the formation of pores.The investigation of transport numbers has shown that whilst the Ca _x Th_1–x O_2–x phase under our experimental conditions is essentially p-type conductor, the Y _x Th_1–x O_2–x/2 phase is essentially ionic conductor.The transport of ion carriers is a diffusion-like process which has activation energy 1·28 to 1·16eV in the Ca _x Th_1–x O_2–x phase and 1·28 to 1·06 in the Y _x Th_1–x O_2–x /2 phase, respectively. The association of impurity ions with anion vacancies provides the maxima in conductivity isotherms.The relative dielectric permittivity of the vacant phase Ca _x Th_1–x O_2–x ranges from 19·2 to 36·2, in the phase Y _x Th_1–x O_2–x /2 from 19·2 to 103, depending on temperature, frequency, and composition of these systems.     

An IR-Radiometer with Internal Signal Modulation

An infrared (IR) radiometer electrical circuit on the basis of photoresistors and photodiodes made of silicon doped with zinc (Si) as well as the narrow bandgap semiconductor alloy Pb_0.78Sn_0.22Te is presented. In the circuit suggested a bridge with the photoreceiver connected to the radiometer input and immediately fed by signal generators functions as a radiation modulator. The threshold sensitivity turned out on a recorder is 2·10^–13 W·Hz^–1/2 (for the n⁺–n–n⁺ structures made of Si, =0.8–l.2m, T=300K); 1.4·10^–15W·Hz^–1/2 (for p⁺–n–n⁺ S-diodes on the basis of Si, =0.8–1.2m, T=300K) and 10^–12W·Hz^1/2 (for photodiodes on the basis of Pb_0.78Sn_0.22Te, =8–13m, T=77K).     

Compositional and structural characterization of strained Si/Si x Ge1−x multilayers and interfaces by high-resolution transmission electron microscopy

A method is described for the quantitative characterization of strained Si/Si _x Ge_1–x multilayers and interfaces by high-resolution transmission electron microscopy (HRTEM) in [110] and [100] crystal projections. The method relies on systematic variations of the image contrast with variations of the local composition x for certain ranges of objective lens defocus f and specimen thickness t and takes tetragonal lattice distortions fully into account. From an extensive study of the image formation process for Si _x Ge_1–x alloys and coherent Si/Si _x Ge_1–x interfaces, ranges of f and t were identified by Bloch-wave and multi-slice image simulations at 400 keV for which a quasi-linear functional relationship between the composition x and the first-order Fourier coefficients of the image intensity exists. By application of a novel image-processing algorithm, which allows a precise measurement of image Fourier coefficients in geometrically distorted lattice images, local composition values x can be determined at near-atomic resolution with an accuracy of x ±0.1 and interface sharpness can be detected at the atomic level. Recent applications of the method to the characterization of interfaces of strained Si _x Ge_1–x layers and short-period Si _m Ge _n superlattices fabricated by different deposition techniques will be presented.