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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 6042-6046 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Magnetic circular dichroism (MCD) of trivalent rare earth doped lithium niobate crystals is reported for the first time. Magneto-optical signals of Nd3+ and Yb3+ ions have been studied at 2 K as a function of the magnetic field strength up to 5 T. This study allows the identification of the Zeeman sublevels of these ions, which can be labeled by irreducible representations (Γ4, Γ5, or Γ6), so that the sign and allowance of transitions can be predicted. From the dependence of suitable MCD spectral lines on the magnetic field strength, the effective gyromagnetic factor of the ground state has been determined for both ions: (gNd)(parallel)=1.4±0.1 and; (gYb)(parallel)=4.7±0.1. © 1999 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5827-5829 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The physical meaning of the standard Preisach model (PM) and of the Preisach distribution p(α,β), particularly for what concerns the problem of the characterization of magnetic interactions, is discussed. It is shown that the standard PM can only describe interactions having a net demagnetizing effect, and that, when the factorization p(α,β)=f(α)f(−β) holds, the simple relation Id/I∞ = 1 − 2(square root of)Ir/I∞, independent of f(x), exists between the Henkel plot remanences Ir and Id. These predictions are compared with recent experimental results. Finally, the relation between magnetic interactions and hysteresis loop shapes is discussed in the frame of a generalized moving PM, where the relation between the applied field Ha and the internal PM field H is of the form H=Ha+Hi(I), where Hi(I) is an odd function of the magnetization I. The shape of p(α,β) and of Hi(I) for nonoriented SiFe alloys is determined and analyzed.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5764-5766 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The connection between hysteresis phenomena and free energy metastable states in magnetic systems is discussed. A random free energy model is introduced, which leads to a stochastic differential equation for the evolution of magnetization in time. We show that the solutions of this equation are equivalent to the Preisach model of hysteresis. The analytical form of the Preisach distribution is calculated. © 1996 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 2504-2508 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results obtained from measurements and spectroscopic analysis of current transients induced in almost ideal silicon n+-p junctions by infra-red stimulation are reported. In particular, by illuminating a reverse biased junction by means of an infra-red emitting diode for a few seconds, a current transient is generated which, at 0 °C, lasts several hours. This can be decomposed, by means of a proper spectroscopic method, into a sum of four exponential contributions with time constants ranging from tens up to thousands of seconds. Similar dark current transients were already obtained for the same junctions when they were stimulated by a change of the reverse bias voltage, without any optical excitation. The spectroscopy of both optical and voltage induced current transients gives four exponential components with the same time constants. Both the dark current and the photocurrent transients are ascribed to the same SiyOx clusters containing hundreds of Si atoms and four types of single energy level defect centers with different localization. While the voltage induced current transients implicate the activation of such defect centers in the p-region near the n+-p interface only, those due to the photostimulation produce their activation throughout the whole n+ region as well. This fact leads to much greater values for the transient photocurrent in comparison to those induced by voltage changes and, as a consequence, to greater reliability and accuracy in the measurements and in the results obtained from their analysis. © 1995 American Institute of Physics.
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Dynamic hysteresis loop shapes and magnetic power losses are studied in nonoriented Fe-Si laminations exhibiting significant excess losses. Measurements are carried out under controlled sinusoidal induction in the frequency range from 1 Hz to 1.6 kHz, at various peak inductions from 0.25 to 1.5 T. Excess losses are found to obey a f3/2 law up to frequencies of 200–400 Hz, depending on peak induction. Beyond this limit, definite deviations are observed, due to eddy current shielding. Detailed information on the flux and field distribution in this high frequency regime is obtained by finite element solutions of Maxwell equations employing the dynamic Preisach model to describe quasi-static hysteresis and dynamic wall processes. The agreement between theoretical predictions and measurements is discussed. © 1997 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5677-5682 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We discuss some properties of the scalar moving Preisach model (MPM) in relation to the description of magnetic interactions. MPM predictions for the behavior of Henkel plots are worked out. The role of the factorization properties of the Preisach distribution and the consequences of the joint presence of mean-field effects and local random interactions are discussed. Literature data are analyzed in the frame of this description, with particular attention to thin-film media with perpendicular magnetization, where mean-field effects are particularly strong. Some of the theoretical predictions are directly tested by hysteresis and Henkel plot measurements performed on SiFe soft alloys. A good agreement, in some cases involving no adjustable parameters, is found.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 387-396 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Proper gettering and annealing processes allow construction of silicon p-n junctions whose current-voltage characteristic either completely obeys the Shockley equation (ideal junctions) or, for reverse bias, has three components (almost ideal junctions): a voltage-independent term, which may be much smaller than the diffusion saturation current, a generation-recombination contribution, and an ohmic component. The last two currents are due to defect centers that have the same activation energy and which are electrically neutral. In preceding works it has been shown that such an experimental finding may be ascribed to four-state traps, i.e., to defect centers that may be empty of carriers, or filled by an electron or a hole, or both, and which are created by localized states, with different positions and energy levels, due to the oxygen. In the present work an experimental system for measuring, at 0±0.05 °C, the current transients produced in almost ideal junctions by changes of the reverse-bias voltage, and an analysis method for performing the spectrometry of such transients are described. It is found that these last a few hours and that they are composed of four exponential terms whose relaxation times range from tens to a few thousands of seconds. Finally, it is shown that such experimental results also can be ascribed to the preceding defect centers generated by SiyOx clusters of a few hundred atoms of oxygen put near the junction interface, which emit carriers through a tunnel-assisted thermal emission.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7463-7465 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interplay between activation volumes and microstructure is investigated in nanocrystalline Fe73.5Cu1Nb3Si13.5B9 (Finemet) alloys. Experiments are performed beyond the Curie point of the amorphous matrix, where relaxation effects are relevant. Measurements are analyzed within a theoretical framework where hysteresis and relaxation phenomena are jointly described. In highly crystallized samples magnetization processes are characterized by a unique length scale. In poorly crystallized samples the system behavior is controlled by a distribution of characteristic volumes related to structural disorder. © 2001 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 4412-4414 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hysteresis, power losses, and the Barkhausen effect are investigated in an Fe-based highly magnetostrictive amorphous material, as a function of applied stress. By means of the static and dynamic Preisach model, and of existing theories of the Barkhausen effect, the results are shown to be compatible with the existence of a characteristic structural length δc, playing a role similar to that of grain size in crystalline materials. At low applied stresses, where the magnetization process is dominated by quenched-in stresses σi, δc is identified with the typical wavelength of σi fluctuations. The theoretical analysis leads to the estimate δc∼70–100 μm and 〈σi〉∼3.5 MPa. © 1999 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4768-4770 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interplay between material microstructure and magnetic hysteresis is studied in rapidly quenched Si–Fe alloys. Two ribbons of different average grain dimension 〈s〉 (35 and 160 μm) were prepared by annealing at different temperatures and studied through two independent approaches: Barkhausen noise measurements, and Preisach analysis of static and dynamic hysteresis loops. In order to monitor the effect of demagnetizing fields on the magnetization process, the strips were progressively shortened from 30 to 10 cm. The correlation length of a domain-wall jump was estimated through the analysis of Barkhausen jump distributions versus apparent permeability. The correlation length of the coherent magnetization reversals controlling excess dynamic losses was estimated through the Preisach analysis of dynamic hysteresis loops. In the sample with lower 〈s〉, both the Barkhausen and the dynamic loss correlation lengths are comparable to 〈s〉, showing that a single structural feature governs all aspects of magnetization reversal. Conversely, in the high 〈s〉 sample, the ribbon thickness competes with 〈s〉 in controlling static and dynamic magnetization processes. © 2000 American Institute of Physics.
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