Thermal conductivity of semiconducting amorphous CdGeAs2

The thermal conductivity of amorphous semiconducting CdGeAs₂ was studied between 100 and 300°K. The Debye model was used for the calculation of the mean free path of phonons which was found to be 10 Å at 300°K and was related to the basic structure units of amorphous CdGeAs₂.Thanks are due to Mrs. J. Beránková, Mr. J. Kapar and Mrs. J. Trepeová for the preparation of the amorphous CdGeAs₂ used in this work and for the measurements of the thermal parameters, and to Dr. J. urek and Dr. S. Kolník from the College of Transport Engineering, ilina, for the sound velocity measurements.     

Influence of Ge and Ag impurities on the thermal conductivity of semiconducting amorphous As2Se3

The thermal conductivity of amorphous semiconducting As₂Se₃ is studied in the temperature range from 100 to 300°K and the influence of germanium and silver impurities is shown. The mean free path of phonons is determined and the observed change of the thermal conductivity is explained by the change of the velocity of sound in amorphous As₂Se₂ containing germanium.Presented by L. toura at the Meeting on Electronic Structure, Optical and Transport Effects in Amorphous and Liquid Semiconductors, Prague, May 1965.The authors are indebted to Dr. J. urek and Ing. I. Turek from the Department of Technical Physics of the College of Transport Engineering in ilina for measuring the velocity of sound in the investigated materials and to Mrs M. Kaparová and J. Trepeová for their help in the experimental work.     

Investigation of GeS (001)

Various possibilities of the preparation of the clean GeS surface were studied. The LEED pattern of the (001) face of the GeS cleaved in situ exhibits clear ordinary reflections. The dimensions of the surface unit mesh agree well to within experimental error (6%) with the corresponding dimensions of the bulk unit cell.The author wishes to thank Dr M.imeková for performing scanning electron microscopy pictures and Dr K.Jurek CSc. for EDAX measurements. Special thanks go to Dr M.Závtová who called my attention to this interesting material.     

On the effect of trapped particles in the regime of cyclotron resonance

The motion of particles in a finite amplitude wave, propagating obliquely to the homogeneous magnetostatic field is discussed. As follows from simple integral properties, in the neighbourhood of Doppler-shifted cyclotron resonance similar trapping effects appear as in a plasma without magnetostatic field. Consequences of this trapping are discussed, in particular, the possibility of a strong absorption of the wave, and the origin of stochastic instabilities caused by the perturbation of an effective trapping potential and leading to the acceleration of particles.The author is indebted to Dr. R.Klíma, Dr. J.Lacina and Dr. P.unka for interesting discussions and to Dr. .Körbel, Mrs. P.Jaroová and Mrs. A.Harmáková for numerical calculations.     

Kinetics and products of crystallization of Fe84−xVxB16 amorphous alloys

Isothermic crystallization of a series of Fe_84–xV_xB₁₆ (x = 0 to 8 at. % V) amorphous alloys was studied by the electrical resistivity, coercivity and⁵⁷Fe Mössbauer spectroscopy methods. Two stages of the process were observed corresponding to the primary -Fe(-V) formation by the growth-of-nuclei mechanism and the eutectic mixed borides — metal crystallization. Concentration dependences of kinetics parameters (Avrami exponent, activation energy) and the changes of electrical and magnetic properties were found and the influence of vanadium on the crystallization process is discussed.Dedicated to Dr. Svatopluk Krupika on the occasion of his 65th birthday.Thanks are due to Prof. L. Potocký, afárik University, Koice, for his kind providing the amorphous ribbons, and to Dr. J. Krejí from the author's Institute for the EDAX analyses.     

Domain wall motion in magnetically soft metallic glasses

The magnetic domains on the surface of amorphous alloys of the composition Fe₄₀Ni₄₀B₂₀ and Fe₅₀Ni₃₀B₂₀ were observed by means of the scanning electron microscope. The details of the experimental arrangement are described that enhance the s.c. type II magnetic contrast and enable us to apply a static magnetic field in the plane of the sample. The displacement of the domain walls under the influence of the applied field were measured and are discussed.Dedicated to Dr. Svatopluk Krupika on the occasion of his 65th birthday.One of the authors (K. Z.) is grateful to Dr. S. Krupika who initiated him in the field of magnetization processes and never lost patience with him in numerous discussions in the course of several decades. We also benefited from the discussions with Dr. I. Tomá after the presentation of our preliminary results at the Second Czechoslovak-Soviet Symposium on the Physics of Magnetic Domains in May 1986.     

Polarization correlation in the scattering of polarized nucleons

Experiments concerning the spin correlation tensorC _pqik in the scattering of polarized nucleons on polarized nucleons are discussed. Relativistic formulae are derived for the experimental quantities. The scattering matrix is directly reconstructed with the help of experimentally measured quantities. The components ofC _pqik are predicted for np-scattering at 630 MeV and are given on graphs.On leave from Faculty of Technical and Nuclear Physics, Czech Technical University, Behová 7, Praha 1, Czechoslovakia.On leave from Nuclear Research Institute, Czechosl. Acad. Sci., e, Czechoslovakia.The authors are indebted to S. M. Bilenskij, J. Bystrický, I. M.Kazarinov, L. I. Lapidus, R. M. Ryndin and Ja. A. Smorodinskij for stimulating discussions and valuable comments and to L. I. Graeva and A. M. Fulkina for their assistance.     

Experimental study of the149Sm(n, α) reaction with thermal neutrons

The cross section of the¹⁴⁹Sm(n, ) reaction for several alpha transitions has been measured. Using an arrangement where only the target is situated in the beam while the detector is placed in some distance aside, the influence of a high background has been successfully eliminated. A detailed analysis of the background has been performed. The obtained resolution in the alpha particle energy (FWHM=65 keV) makes it possible to distinguish seven transitions for which average cross sections for the thermal neutron spectrum withT= 400 °K have been evaluated.The authors wish to thank to Mrs. J. Tomíková for supplying the samarium targets, to Messers J. Hofman, J. Novotný, B. Malý for design of the electronic equipment and to Mr. V. Kvítek and Mr. P. Zajíek for their assistance during the experiment.     

States and homomorphisms on the Pták sum

Summing of a Boolean algebra and a quantum logic has been defined by P. Pták and studied by, e.g., V. Jani, Z. Rieanová, O. Nánásiová, and C. A. Drossos. It was shown that there is a special case when this structure is a direct product. Drossos has studied the connection between this structure and a Boolean power. In this paper we investigate the conditions when the Pták sum is a free product and when the connection is between the center ofL and the structure of states onBL.     

Determination of the optical activation energy of germanium by the method of photoelectric lines

From the dependence of the photovoltage of the p-n junction on the temperature of black body radiation, with which the junction is illuminated, the optical activation energy of germanium E₀=0.62±0.02 eV at 300 K is determined. On the basis of this measurement, and an analysis of the conductivity and optical measurements given in the literature, reasons are presented which render probable the conclusion that the optical activation energy of germanium is equal to the width of the band of forbidden energy values, of magnitude E_G=0.75–4.10^–4T eV.It is my agreeable duty to extend my thanks to K. mirous for the preparation of suitable samples, and A. Abrahám and V. Ondíková for their aid in the experimental work.     

Microhardness and structure transformations of Al-15 at.% Zn alloy aged at elevated temperatures

The microhardness changes on ageing in single crystals of the Al-15 at.% Zn alloy at the temperatures of 201 °C and 222.5 °C are presented in this paper. The gradual decomposition of the solid solution was simultaneously studied from X-ray diffraction measurements. The results reveal the mutual correlation between the individual structural stages and the microhardness of this alloy.Cukrovarnická 10, Praha 6, Czechoslovakia.In conclusion the authors wish to express their thanks to Doc. Dr. V. Syneek CSc. for many stimulating discussions, to Ing. J. Laek CSc. for the careful chemical analyses of the investigated alloy and to Ing. P. Bartuka CSc. for the private communication of his results from the electron-microscopic study. Our thanks are also due to Mr. Z. iký and Mr. J. Bauer for assistance in measurements.     

A study of the nuclear magnetic resonance of isotope Fe57 in hematite

The results of studying the nuclear magnetic resonance of isotope Fe⁵⁷ in weak ferromagnetic hematite -Fe₂O₃ for different types of samples are presented. Measurements of the temperature dependence of the nuclear magnetic resonance frequency in the range of 250–820°K, as well as the dependence of the signal intensity on temperature, the orientation and intensity of the static and h.f. field were carried out. The interpretation of the experimental results is based on the assumption that the signal originates from the nuclei inside the domain walls. The abnormally high value of the enhancement factor of the h.f. field is explained by the closeness of the nuclear magnetic resonance frequency and the resonance frequency of the domain walls.In conclusion the author expresses his thanks to Prof. J. Bro for his valuable advice and comments when preparing this paper; to Prof. R. Rost, Dr. Z Hauptman and M. Vichr for providing the samples; to Dr. V. Houdek for measuring the Néel temperature and to J. Pavlíek for substantial help in the measurements     

Control of plasma position in the castor tokamak

A servo-system for control of plasma position in the CASTOR tokamak is described. The plasma is maintained in the prescribed position with an accuracy of 3 mm.The author thanks to Mr. J. Zelenka who performed a great deal of mechanical and cablelaying work. Dr. F. áek is gratefully acknowledged for his support.     

The MSR-investigation of antiferromagnetic phase transitions in erbium

The muon spin relaxation rate (T) in an orientated polycrystalline sample of erbium constructed of large monocrystals has been measured for temperatures 20 <T<300 K. It has been shown that the (T) for erbium is bounded from above asT T_N, whereT _N=84.4 K is the Néel temperature. This fact may be explained by assuming that atT=T_N erbium undergoes a weak phase-transition of the first order.     

Some physical properties of single crystal manganese ferrites

The paper gives the results of measuring the Curie temperatureT _c , the Seebeck coefficient and the activation energy of electrical conductivity on single crystal samples of manganese ferrites prepared by two different methods. In the system Mn _x Fe_3–x O_4+y changes in the course of the quantities T_c, and are observed in the neighbourhood ofx=1 andx=1·9. A qualitative explanation of these courses is given and the influence of oxygen non-stoichiometry is discussed.The authors would like to thank Dr. S. Krupika for valuable remarks and discussions, E. Kitzinger for the X-ray analysis and A. Novák for careful chemical analysis.     

μSR studies in the heavy fermion systems UNi2Al3, UPd2Al3 and U2PtC2

We have performed Muon Spin Relaxation (SR) measurements of several heavy fermion systems: UNi₂Al₃ (single crystal), UPd₂Al₃ (single crystal) and U₂PtC₂ (polycrystal). ZF -SR measurements of UNi₂Al₃ show magnetic order below the Néel temperatureT _N=4.6K, with the muon precession frequency(T 0)=2.5MHz at low temperatures. The local field distribution obtained at low temperatures in UNi₂Al₃ resembles that of the incommensurate spin density wave (SDW) system (TMTSF)₂PF₆, suggesting an incommensurate spin arrangement in UNi₂Al₃. TF -SR measurements give the penetration depth(T 0)=6100Å for UPd₂Al₃ and(T 0)=7000Å for U₂PtC₂ respectively. Since UPd₂Al₃ and U₂PtC₂ are clean superconductors (/l-0), we can combine n _s/m^* with the Sommerfeld constant n _s ^1/3 m^* to calculate the Fermi temperatureT _F ^3/4–1/4, which represents the characteristic energy scale of the superconducting carriers. We obtainT _C/T_F 0.01 for both UPd₂Al₃ and U₂PtC₂, comparable to other exotic superconductors, but quite different from simple metal BCS superconductors, whereT _C/T_F 0.01.     

Die Röntgenolumineszenz der aus der Schmelze Gezüchteten Kristalle von NaCl: Fe

The X-ray luminescence of NaCl crystals with Fe(III) from the melt was studied. The conditions of the occurrence and colour of this luminescence and the luminescence centres are discussed from the point of view of the content of oxygen in crystals.

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Die Verfasser möchten Herrn RNDr. A. Bohun für seine Interesse und die Unterstützung dieser Arbeit herzlich danken. Sie danken ferner Herrn Ing. K. Polák für die Mitarbeit bei der Messung der Spektralzerlegung der Lumineszenz und Frl. H. paková und Herrn A. Cihlá für ihre wirksame Hilfe bei den technologischen Arbeiten.     

Highly oriented thin oxide films on single crystals of Fe-Si alloys

Under certain oxidation conditions, highly oriented oxide films grow on single crystals of some Fe-Si alloys. A typical two-phase film of this kind was studied in order to reveal the orientational relationships between-Fe₂O₃ and Fe₃O₄ on the (001) surface of the substrate. The orientational relationships were determined from reflection high-energy electron diffraction patterns where reflections from both oxides were present.The authors are indebted to Ing. B. esták and Ing. S. Kadeková who made possible the preparation of single-crystalline samples of Fe-Si alloys in the Institute of Physics, Czechoslovak Academy of Sciences; to Dr. M. Rozsíval (Institute of Solid State Physics, Czechoslovak Academy of Sciences) who enabled the authors to use the electron diffraction apparatus; and to Dr. A. Línek (Institute of Solid State Physics, Czechoslovak Academy of Sciences) for helpful discussion.     

The X-ray spectrum of germanium doped with Ga and Sb

The K ₂ emission band as well as the L _1,2 region of the X-ray spectrum of pure germanium and germanium doped with Ga and Sb, resp., are compared. In contrast to papers [1], no changes were found.The authors thank Dr. Z. Trousil for preparing the single crystals, Ing. L. toura, DSc, for the determination of the concentration of the doping elements in germanium single crystals and V. ídová for carefully performing some of the measurements.     

Study of the influence of iron and lanthanum oxides on the band structure of Pb(Zr,Ti) O3

The measurements of diffuse reflectance spectra in the range of 400; 2500 nm and of photoacoustic spectra in the range of 350; 800 nm were used for the study of the influence of iron (III) oxide and lathanum oxide additions on the band structure of polycrystalline lead zirconate — lead titanate solid solutions. The molar ratio of zirconium and titanium in the studied solid solutions was 60 40, and the concentrations of the dopants werex FeO_1.5, andy LaO_1.5, werex 0; 0·05 mol, andy 0; 0·10 mol, respectively. The diffuse reflectance spectra were expressed in terms of the Kubelka-Munk function values versus incident electromagnetic radiation energy. These dependences were decomposed into partial absorption bands using a computer. Transitions of charged carriers between energy levels or bands which differ mutually by the energy of 0·9, 1·2–1·3, 1·6, 1·65–1·7, 2·4–2·5, 2·75–2·8, 2·9–3·2, 3·4–3·8 eV, were identified. Their intensities depend on the concentration of Fe and/or on La in the Pb(Zr_0.60 Ti_0.40) solid solutions.The authors are very grateful to Mrs. Iva Havlasová, Vra Andrsová, Ing. Jan Netuka, and Mrs. Liana Karlíková from the first authors' institute, for their technical assistance.