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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time effects associated with domain-wall stabilization processes are investigated at temperatures ranging from 80 to 420 K, for yttrium iron garnet polycrystalline samples sintered in different atmospheres. A very different behavior for samples sintered in high and low oxygen partial pressures is found. Above 0.1 atm the isochronal relaxation spectra show a peak around 180 K that could be associated with an electron diffusion controlled domain-wall relaxation. The activation energy for the process is close to 0.4 eV. Below this pressure, the spectra show both positive and negative peaks as a result of the competition between disaccommodation and accommodation processes. These peaks are closely temperature spaced in the neighborhood of 130 K, and the relaxation mechanism responsible for this behavior is not yet clear.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 6208-6210 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It has been recently suggested that periodic antidot arrays in magnetic media could be a suitable system for high density data storage because hard axis magnetic switching has remanence and hence, memory. In this work a numerical micromagnetic study of periodic antidot permalloy arrays is presented. Remanent states are obtained after saturation of the sample along the hard axis direction for different antidot sizes w (0.32 μm≤w≤2.16 μm) and different separation distances d between antidots (w/2≤d≤3w). Our micromagnetic model allows us to study these systems beyond the experimental results presently available so that we can explore the high density limit. The signal to noise ratio decreases significantly for separation distances d≥w and increases steadily with the antidot size w in the range analyzed. The remanent configurations are similar to the experimental data obtained by scanning Kerr microscopy. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford BSL : Blackwell Publishing Ltd
    Grass and forage science 53 (1998), S. 0 
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The effects of plant harvest stage, autumn harvest dateand cultivars on alfalfa production and quality weredetermined in a 3-year field experiment established in1992. Harvesting stage influenced annual yield andquality. Late bud-first flower harvests increased harvestfrequency and forage quality in comparison with har-vestingat the full bloom stage while decreasing dry-matteryield by 18% (25·5 vs. 21·6 t ha 21 ). Harvestingstage significantly affected autumn forage productionand quality and yield at the first spring cut. Harvests atfull bloom allowed greater autumn and spring regrowththan cutting at the late bud stage, possibly because ofthe accumulation of higher root reserves. Autumn har-vestsand cultivar significantly influenced the yields atthe first spring cut in any growing season. Cuttingbefore the first frost in autumn reduced the vigour ofboth cultivars, and the subsequent yield at the first cutin any year, in comparison with harvests taken after ornear the first autumn frost. It is concluded that theeffects of the stage of harvesting alfalfa on dry-matterproduction and quality are important in theMediterranean environment of the Ebro Valley; theeffects of autumn management were observed mainlyon the yields of the subsequent first cut in spring but noton the total annual production.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6574-6576 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic relaxation in ceramic cylindrical samples of BiPbSrCaCuO high Tc superconductors has been studied as a function of applied magnetic field for a constant decay rate of that field strength. We have analyzed the variation of the ac susceptibility versus time just after removing the magnetic field. Data have been obtained by means of an inductive technique from 1 to 3600 s, with magnetic fields that range from 10 to 100 Oe, and by switching off the field at a constant rate of 25 Oe/s. The field dependence of the thermally activated parameters has been obtained within the framework of the Anderson–Kim theory and using the so-called box distribution of energies. Anderson–Kim considered a logarithmic decay of the magnetic flux governed by an effective energy U=U0−FVX, where U0 is the pinning energy, V is the activation volume, X the pinning length, and F the driving force density. In this case we have found a field dependence of the form H−n for the pinning energy, with n close to 2 and temperature dependent. However, we have observed that the box distribution, which assumes the existence of a continuous energy spectrum, shows no field dependence for the effective energy. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The frequency dependence of the ac susceptibility in polycrystalline samples of YBaCuO has been studied at the ac field range 0.06–1.2 Oe. The curve of the real part of the susceptibility χ' exhibits two drops, the first one close to Tc and the other well below Tc which could correspond to screening behavior of the grains and grain boundaries, respectively. The imaginary part of the susceptibility shows only a peak below Tc which is related to hysteresis losses at the grain boundaries. The peak corresponding to intragrains hysteresis losses is very small and appears masked by the losses of the intergrains. In the range of 1–20 kHz, the onset temperature of χ' showed no frequency dependence. However, the width of the transition decreases lightly and there is a small shift in the peak of χ‘ to higher temperature as the frequency increases. This behavior could be explained in terms of the thermally activated Anderson flux creep. The shift depends on the amplitude of the measuring field. The activation energy for flux creep ranges from 6.4 eV at 0.02 Oe to 3.23 eV at 1.2 Oe in the zero-field-cooled measurements and from 3.41 eV at 0.02 Oe to 1.41 eV at 1.2 Oe in the field-cooled measurements.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this communication we present in a systematic way experimental data on ferromagnetic resonance (FMR) linewidths of polycrystalline nickel ferrites (NixFe3−xO4 with 0.8〈×〈1.5) from 8 to 12.4 GHz and from 26.5 to 60 GHz. Data from 26.5 to 60 GHz were taken at room temperature while measurements at X band have been carried out from 77 to 400 K. Neither in X band nor from 26.5 to 60 GHz was a clear frequency dependence found. Classical contributions to the FMR linewidth according to Sparks' outline are analyzed in the whole range of frequencies from 8 to 60 GHz. Contributions of the porosity, anisotropy, slowly and rapidly relaxing impurities, valence exchange and eddy current mechanisms are considered. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polycrystalline yttrium–iron–garnet (YIG) samples were sintered in air at temperatures ranging from 1350 to 1450 °C. Ferromagnetic resonance measurements have been accomplished at 11 GHz from 77 to 350 K. The different contributions to the linewidth have been analyzed. These results are compared with previous measurements of magnetic disaccommodation in the same samples. A qualitative relationship between both kind of measurements for polycrystalline YIG samples by means of an induced anisotropy formalism is provided. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Biotechnology progress 11 (1995), S. 221-223 
    ISSN: 1520-6033
    Source: ACS Legacy Archives
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 427-429 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Disaccommodation and ferromagnetic resonance measurements for single crystal titanium-doped lithium ferrites are presented. Magnetic disaccommodation is performed at 1 kHz from 77 to 400 K while ferromagnetic resonance is carried out at 11 GHz from 77 to 300 K. Ferromagnetic resonance line shape asymmetry and anisotropy field data are also shown. A relationship between the asymmetry and the disaccommodation spectra is suggested. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7585-7587 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Micromagnetic simulations of switching processes in planar square magnetic nanoelements are presented. Nanosquares of size "a" in the range 10 lex〈a〈110 lex (lex being the exchange length, lex=(A/2πMs〈sup ARRANGE="STAGGER"〉2)1/2) and thickness "t", 0.25 lex〈t〈2 lex have been studied. Two different switching modes have been observed. The first one is basically found for very small nanoelements and it is close to uniform rotation while the second one takes place in the large nanosquares and presents an intermediate state. Good agreement of the computations with recent experimental measurements in Supermalloy is achieved. The shape of the hysteresis loops, the values of the coercivity, and the maximum in coercivity dependence with size are reproduced by the simulations. Furthermore, the two reversal mechanisms are shown to be the cause of such maximum in coercivity such as the different shapes of hysteresis loops. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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