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  • 11
    Electronic Resource
    Electronic Resource
    Magnetic excitations and phase transition of CsFeBr3 in an external magnetic field (1990)
    Springer
    The European physical journal 81 (1990), S. 75-82 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In CSFeBr3 the Fe2+ ion with effective spin one has locally a singlet ground state (m=0). The antiferromagnetic interactions between neighbouring Fe-ions are too weak as compared with the anisotropy constant to introduce long range order in the absence of an external field. By inelastic neutron scattering we studied the magnetic excitations in an external magnetic field up to 5 Tesla applied along thec-axis. A linear Zeeman splitting was observed with a Landé factorg=2.4. The field renormalizes the dispersion curves in such a way that the exchange interaction has decreasing influence with increasing field. Theoretical calculations according to the excitonic model of Lindgård describe the experimental results very well. At 4.1 Tesla a phase transition appears to a commensurate long range order with a 120° arrangement of the spins in the hexagonal plane. Within the limits of experimental observation this phase transition has no influence on the dynamical behaviour. No critical phenomena could be observed. The dynamical structure factor |G j(ℚ)|2 of the lower Zeeman split modes decreases with increasing field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01454216
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  • 12
    Electronic Resource
    Electronic Resource
    Temperature and magnetic field dependent correlations in the singlet ground state system CsFeBr3 (1992)
    Springer
    The European physical journal 86 (1992), S. 257-262 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The magnetic excitations in CsFeBr3 have been measured with inelastic scattering of cold neutrons to high precision at 80 mK. The fact that the lowest frequency mode softens with decreasing temperature but stabilizes at 0.11 THz below 2.5 K is the indication that CsFeBr3 remains a SGS system forT→0. From dispersion curves measured earlier in a magnetic field along the chain axis experimental intensities were derived and in turn correlation lengths. Correlation lengths were also calculated using the new parameters for exchange and anisotropy. The experimental results and the calculations both show that the correlation lengths increase for increasing magnetic field, flatten off around the phase transformation at 4.1 Tesla with a maximum of about 35 Å and then decrease again for higher fields. No critical phenomena connected with this phase transformation could be detected. The “Mirror Mode” published earlier was found to be of spurious origin due to double scattering. It does not exist.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01313834
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  • 13
    Electronic Resource
    Electronic Resource
    Magnetostrictive and quadrupolar anisotropy in nuclear magnetic fcc systems (1992)
    Springer
    The European physical journal 89 (1992), S. 305-311 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The spin hamiltonian for nuclear magnetic order in copper is investigated with respect to magnetoelastic couplings to the lattice. These arise due to the dipolar, Ruderman Kittel and the quadrupolar interaction. While the latter is quenched for the ideal fcc-lattice, it is found that for copper it will dominate the magnetoelastic terms of the nuclear spin hamiltonian. The absolute size of the quadrupole contribution is determined by the effective charge and (anti-) shielding effects. This interaction can give rise to an effective anisotropy in the fcc-system which can be quite large compared to the small stabilisation energies for nuclear order in copper. Consequences for the nuclear ordering in copper are briefly discussed and compared to the available experimental and theoretical data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01318161
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  • 14
    Electronic Resource
    Electronic Resource
    Elementary excitations in easy-plane Heisenberg ferromagnets (1981)
    Springer
    The European physical journal 42 (1981), S. 241-244 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We study the influence of the non-diagnonal terms in an easy-plane Heisenberg ferromagnet on the cross-section for inelastic neutron scattering from single spin-wave states. We show that these terms modify the wavevector dependence of the cross-section for unpolarized neutrons, and the created polarization. An appropriate experiment on CsNiF3, for example, should be a good test of these predictions, and would eventually clarify some uncertainties about the appropriate Boson Hamiltonian for an easy-plane ferromagnet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01422028
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  • 15
    Electronic Resource
    Electronic Resource
    Magnetic excitations of CsFeCl3 in an external magnetic field parallel to the hexagonal plane (1994)
    Springer
    The European physical journal 95 (1994), S. 13-21 
    Details
    ISSN: 1434-6036
    Keywords: 75.10.Dg ; 75.25.+z ; 75.30.Et
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In CsFeCl3 the Fe2+-ion with effective spin one has locally a singlet ground state (m s =0). The ferromagnetic interactions along thec-direction and the anti-ferromagnetic interactions perpendicular to it are too week as compared to the anisotropy to introduce longrange order in the absence of an external field. By inelastic neutron scattering we have investigated the excitation spectrum in an external magnetic field up to 6 T applied perpendicular to thec-axis. Preliminary measurements in zero field show that dipolar effects lead to a shift of the minimum of the dispersion curve away from theK-point. We show that with increasing magnetic field the whole dispersion sheet is shifted towards higher frequencies and a splitting appears. With the help of a local Hamiltonian which neglects exchange interactions between all neighbours we give a qualitative explanation of the intensity of the magnetic excitations in dependence of the magnetic field. A more sophisticated theory (RPA-diagonalisation of the Heisenberg-Hamiltonian that is used to describe the magnetic behaviour of CsFeCl3) yields — apart from a mismatch for the modes at high energy transfers — a satisfactory description of the magnetic excitations of CsFeCl3 in dependence of the magnetic field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01316838
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  • 16
    Electronic Resource
    Electronic Resource
    Momentum distributions of projectile fragments produced in the cold and hot fragmentation of relativistic136Xe and197Au projectiles (1993)
    Springer
    The European physical journal 346 (1993), S. 43-46 
    Details
    ISSN: 1434-601X
    Keywords: 25.70.Np
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The longitudinal-momentum distributions of projectile fragments from 0.8 A GeV136Xe and 1 A GeV197Au projectiles impinging on targets of beryllium and aluminium, respectively, have been measured using the projectile-fragment separator FRS at GSI. Different momentum distributions have been found for two different classes of fragmentation processes: the abundant hot fragmentation with several nucleons evaporated from the prefragments, and the rare cold fragmentation with only protons removed from the projectile, but no nucleons evaporated. The data are compared to model calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01290780
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  • 17
    Electronic Resource
    Electronic Resource
    Experimental study of the spindynamics in the 1-D-ferromagnet with planar anisotropy, CsNiF3, in an external magnetic field (1983)
    Springer
    The European physical journal 53 (1983), S. 117-142 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The results of a detailed inelastic neutron scattering study of the spindynamics in CsNiF3 in an external magnetic field are presented. Results have been obtained for different combinations of the correlation function 〈S α Sα〉 (α=x, y, z) in order to analyse theH, T, q c-dependence of both, the central component and the spinwave scattering. These results cannot be explained by a multispin-wave theory alone, but it is necessary to introduce solitons in order to describe the experimental findings. It is found that under certain conditions the contribution from solitons and from two-spinwave processes have the same size. These results show that the spindynamics in this system in fields 2.5kOe〈H〈10kOe and5K≦...15K are similar to that in a sine-Gordon system. ForT〉15K this picture breaks down probably due to the finite size of the easy plane anisotropy energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01304200
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  • 18
    Electronic Resource
    Electronic Resource
    Influence of growth conditions on the structural, optical, and electrical properties of ZnSe films (1992)
    Springer
    Applied physics 54 (1992), S. 455-459 
    Details
    ISSN: 1432-0630
    Keywords: 61.10.-i ; 78.55.-m ; 72.80.Ey
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract ZnSe films were grown by chemical vapour deposition on GaAs substrates. The influence of the source temperature (between 820 and 900° C) and the substrate temperature (between 620 and 790° C) on the film properties were investigated by Hall measurements, X-ray diffraction, and photoluminescence. With respect to blue luminescent devices the ratio of excitonic to deep level transitions was found to be optimum at low growth rates when the source temperatures were kept below 840° C. P-type conduction up to a net carrier concentration of 8×1018 cm−3 could be obtained by substrate temperatures above 700° C. Lattice contraction versus substrate temperature pointed to a reduced incorporation of donors at higher growth temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00324171
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  • 19
    Electronic Resource
    Electronic Resource
    Reflection-scanning near-field optical microscopy and spectroscopy of opaque samples (1994)
    Springer
    Applied physics 59 (1994), S. 103-108 
    Details
    ISSN: 1432-0630
    Keywords: 07.60.Pb ; 07.65.Eh ; 78.65-s
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Opaque samples are imaged by Scanning Nearfield Optical Microscopy (SNOM) in reflection mode: A quartz glass fiber tip is used both to illuminate the sample and to collect light locally reflected from or emitted by the surface. The collected light is coupled out by a 2×2 fiber coupler and fed into a grating spectrometer for spectral analysis at each sampled point. The tip-sample distance is controlled by a shear-force feedback system. The simultaneous measurement of topography and optical signals allows an assessment of imaging artifacts, notably topography-induced intensity changes. It is demonstrated that an optical reflectance contrast not induced by topographic interference can be found on suitable samples. Local spectral analysis is shown in images of a photoluminescent layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00332201
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  • 20
    Electronic Resource
    Electronic Resource
    Response of metal-insulator-metal point contact diodes to visible laser light (1981)
    Springer
    Applied physics 25 (1981), S. 7-12 
    Details
    ISSN: 1432-0630
    Keywords: 06.30 F ; 07.62 ; 73.40 R
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Video response and mixing behaviour of metal-insulator-metal point contact diodes have been investigated for visible laser light. Thermally enhanced tunneling is shown to dominate the dc detection behavior of those diodes, while mixing of frequencies being more than several MHz apart is a more complex phenomenon involving thermal, field-and photo-assisted tunneling. In further experiments the potential of point contact diodes for optical heterodyne spectroscopy was examined. Two green laser lines of 122 GHz frequency difference were mixed with the second harmonic of an appropriate microwave frequency, generated simultaneously on the diode. The modestS/N ratio achieved has to be assigned to the different behaviour of metal-insulator-metal diodes in the visible and rf range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00935384
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