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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 3626-3633 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of heat treatment on conventional magnetic properties and Barkhausen noise were studied in ferromagnetic amorphous Fe40Ni38Mo4B18 during a half magnetization cycle for both amorphous and crystallized states. The coercivity, Hc, was low in the amorphous specimens and maximum as the crystallization starts, and decreased with further annealing. The differential permeability near to the Hc, μc, was high in the amorphous specimens and minimum at the onset of crystallization, then increased with annealing. The single peak behavior of the Barkhausen noise (BN) envelope was a common feature in both amorphous and crystallized specimens, and the variation of peak height with heat treatment was similar to that of μc. The magnetic anisotropy energy constant, Ku, was lowest when the crystallite started to nucleate in the amorphous specimen, and increased as the crystallite size grows. The difference between ribbon and transverse directions of BN characteristics such as BN energy, peak height of BN envelope, Hp, and corresponding field strength to Hp, respectively, was the lowest at the onset of crystallization, and increased with Ku. A model was proposed to predict the linear relationship between the magnetic anisotropy energy constant detected by torque measurement and the one evaluated by BN measurement.
    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 89 (2001), S. 7496-7498 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electromagnetic properties of an Ag2O doped and an undoped BiPbSrCaCuO superconductor were evaluated to investigate the effect of the pinning center on the magnetic shielding and suspension/levitation phenomena. The residual magnetization M=M+–M− increased with the dopant concentration, a maximum for 2% doping, wherein a fine uniform dispersion of Ag particles was observed. The fine Ag particles form a cluster with increasing dopant as the particles condense with each other and grow, consequently does the number of flux passing through decreases, so the magnetization M decreases. This result indicates that M is proportional to the number of magnetic flux lines passing through the sample, because the smaller the particle size the larger the ratio of the surface area to the volume. Magnetic shielding was evaluated by measuring the induced voltage in the secondary coil by placing the sample in between the primary coil. The voltage was initially set to 0.5 V, and decreased to 0.17 and 0.28 V, respectively, for the undoped and 2% Ag2O doped samples. The much less change in the induced voltage for the 2% doped sample is attributed to increased flux shielding by shielding the vortex current. Simultaneous stable levitation and suspension of 2% Ag2O doped disk samples weighing 0.3 g were observed, respectively, above (3 mm) and beneath (2 mm) a toroidal permanent magnet under a field cooled condition. The role of flux pinning is discussed to account for the phenomena by considering the hysteretic force function. © 2001 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5447-5449 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The giant magnetoimpedance (GMI) has been measured in weak-field-annealed Co-based amorphous ribbon as functions of both the annealing field, Ha, and the measuring frequency. The GMI profile measured at 0.1 MHz shows a typical two-peak behavior for the sample with Ha less than 50 mOe. The GMI peak in the region where the applied field is antiparallel to the annealing field decreases with Ha, showing an asymmetry in the GMI profile. Eventually, the GMI peak in the antiparallel-field region disappears, and a drastic step-like change in the GMI peak is revealed for an applied field which is parallel to the annealing field of 500 mOe. The asymmetric GMI phenomenon for the 0.1 MHz measuring frequency, the so-called "GMI valve," is due to a peculiar domain structure, which occurs in the sample surface during the field annealing. The GMI peak in the parallel-field region appears again for measuring frequencies over 0.5 MHz due to the remarkable contribution of the magnetization rotation to the GMI. © 1999 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 7115-7117 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The changes in soft magnetic properties on amorphous Fe73.5Cu1Nb3Si13.5B9 alloy after neutron irradiation are studied by complex permeability spectra, magnetoimpedance ions and M–H curve measurements. The total integration fluence of fast neutrons (nf,En〉1 MeV) is varied from 1.92×1014nf cm−2 to 4.85×1016nf cm−2. Two different types of relaxation processes in permeability spectra, which were observed in low and high frequency regions, are related to the domain wall motion and the rotational magnetization, respectively. As neutron irradiation fluence increases, the permeability due to domain wall motion decreases but the permeability due to rotational magnetization increases. The anisotropy field estimated from magnetoimpedance profile decreases with neutron irradiation fluence. The measurement of M–H curves shows the improvement of softness after neutron irradiation of 4.85×1016nf cm−2, due to the enhancement of rotational magnetization. © 2000 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 2660-2664 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The perturbation theory of Auld [Acoustic Fields and Waves in Solids (Wiley, New York, 1973), Vol. II, p. 294], which describes the effect of a subsurface gradient on the velocity dispersion of surface waves, has been modified to a simpler form by an approximation using a newly defined velocity gradient for the case of isotropic materials. The modified theory is applied to nitrogen implantation in AISI 4140 steel with a velocity gradient of Gaussian profile, and compared with dispersion data obtained by the ultrasonic right-angle technique in the frequency range from 2.4 to 14.8 MHz. The good agreement between experiments and our theory suggests that the compound layer in the subsurface region plays a dominant role in causing the dispersion of acoustic surface waves.
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