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  • 1990-1994  (6)
  • 1
    Electronic Resource
    Electronic Resource
    Uniaxial magnetic anisotropy in Fe-rich 2:17 compounds with sp substitutions : The 6th joint magnetism and magnetic materials (MMM)−intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6737-6739 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic properties of single-phase 2:17 compounds of the composition Sm2Fe17−x−yCoyMx with M=Al and Ga and x and y in the range 0–5 are reported. The Curie temperature is found to increase for the y=0 samples with increasing x up to a maximum at x=3 for M=Al and x=4 for M=Ga and a monotonic increase with increasing y for all x and M. Samples with x〈2 showed an easy-plane magnetic anisotropy at room temperature while samples with x(approximately-greater-than)2 showed a single-phase uniaxial anisotropy. The addition of Co is seen to increase the saturation magnetization and the anisotropy field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358187
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Structure sensitivity of magnetization processes at the spin-reorientation transition in Nd2Fe14B : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5562-5564 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Calculations based on different micromagnetic models were carried out in order to describe the behavior of the ac susceptibiIity in the temperature range of the spin-reorientation transitions in hard magnets. It was found that the rotational susceptibility shows a sharp cusp at the transition temperature, while the contribution due to an increase in the domain- wall mobility is less significant. As well, there is a significant contribution of domain- wall processes to the overall susceptibility over the entire range of temperatures studied (80– 180 K). For randomly oriented bulk samples, the susceptibility cusp has been experimentally observed. The susceptibility of randomly oriented powders shows only a moderate temperature dependence below the transition, followed by a sharp decrease at the transition temperature. The frequency dependence of the susceptibility showed the behavior expected for conducting samples, proving that domain-wall dynamics (e.g., aftereffects, lattice-defect–domain-wall interactions, etc.) do not play a role in the observed temperature dependence of the susceptibility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347950
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Time-dependent response and the de Almeida–Thouless line in R 1:2:3 superconductors (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5058-5060 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: As shown recently, the time-dependent response in high-temperature superconductors can be well evaluated on the basis of the classical theory of first-order relaxation processes, if the temperature is low enough. In this article we extend our investigation to the high-temperature limit and show that the decrease of the logarithmic relaxation rate is an experimental consequence of the relaxation model and not a critical slowing down. On the basis of a comparison of the different classical relaxation processes and superconductive time-dependent response the special features of the superconductor can be interpreted. It is shown that all irreversible relaxation results in thermal hysteresis as a consequence of the difference between the time scale of the relaxation and the experiment. This feature introduces difficulties into the experimental determination of the de Almeida–Thouless lines.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344669
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Variable frequency two-phase ac susceptometer for use in dc bias fields over the temperature range of 4.2 to 300 K (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 793-796 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A system has been designed and constructed in order to detect differential ac susceptibility as a function of temperature between 4.2 and 300 K. A dc bias field in the range of 0–50 kOe is provided by a superconducting magnet. The available ac field range is 0–1 Oe. Using the reference source of a PAR lock-in amplifier, the measurements can be carried out in a frequency range of 0.1–10 kHz. A differential amplifier circuit is used to accurately detect the susceptibility signal. As this provides both in-phase and out-of-phase compensating signals, both the real and imaginary components of the susceptibility can be detected even when using a single-phase lock-in amplifier. The circuit diagram and principle of operation as well as the calibration procedure and data processing methods are described in detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142086
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Asymmetry between flux penetration and flux expulsion in Tl-2212 superconductors (1993)
    Springer
    Journal of superconductivity 6 (1993), S. 185-189 
    Details
    ISSN: 1572-9605
    Keywords: Thallium cuprates ; superconductivity ; magnetic hysteresis ; irreversibility ; flux pinning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract dc magnetic hysteresis as well as flux penetration and flux expulsion were investigated in Tl2−y Ba2CaCu2O8−x polycrystals and monocrystals. All measurements were performed at 35 K and in the 0–5 T field range. Hysteresis measurements revealed an irreversibility field of about 2 T. Existing models predict identical field-cooled (fc) and zero-field-cooled (zfc) magnetizations and vanishing time dependence above this field. Although the identical fc and zfc magnetizations are in fact observed, the time dependence vanishes only for flux penetration after zero-field cooling; a remanence is preserved after field cooling and decays with a finite relaxation rate. Activation energies calculated on the basis of the thermal activation model display a pronounced field dependence, and arelower for flux penetration than for flux expulsion in high fields (H≥3 T) for all orientations. This behavior of extreme layered superconductors contradicts classical theoretical models and questions the original definition of the irreversibility line as well. All of our results are consistent with the recent theory of lock-in transition, and can be well interpreted by using those principles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00625745
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Magnetic properties of Sm2Fe14−xCoxAl3 compounds (1994)
    Springer
    Journal of materials science 29 (1994), S. 5333-5336 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Compounds in the series Sm2Fe14−x Co x Al3 (x = 0, 1,2, 3, 4 and 5) have been shown to be of the Th2Zn17 structure. The Curie temperature is found to increase monotonically from a critical temperature,T c equal to 471 K for thex=0 sample, toT c=681 K for thex=5 sample. X-ray diffraction measurements of magnetic field oriented powders showed that all compounds exhibit a room temperature uniaxial anisotropy. Magnetization measurements show that the magnetic anisotropy of Sm2Fe14Al3 can be increased substantially by the substitution of even a small quantity of Co for Fe. Results are discussed in terms of possible applications of these compounds as particulate recording media.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01171544
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    Paper (German National Licenses)
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