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  • 1
    Electronic Resource
    Electronic Resource
    A study of the dynamics of magnetic disaccommodation in amorphous ferromagnets. II. Theoretical considerations (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4724-4727 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The results obtained in part I are interpreted in terms of the viscosity field arising from independent processes of directional ordering for magnetic defects dispersed in the amorphous structure and interacting with the magnetization vector. A specific model is developed in order to take into account the changes in the ordering kinetics induced by the periodic magnetization rotations described in part I. This model, however, requires that the magnetic induction remain constant during the whole measurement; as a consequence, the model's predictions cannot be directly compared with the experimental results, obtained instead at constant applied field. This difficulty is overcome by deriving a general relationship between the magnetic-induction decay and the viscosity field kinetics for an arbitrary number of half-periods of the square-wave field. The agreement of our theory with the experimental results turns out to be quite satisfactory. As consequence, the ordering processes responsible for the magnetic aftereffect in amorphous ferromagnets may be described as essentially uncorrelated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346153
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  • 2
    Electronic Resource
    Electronic Resource
    A study of the dynamics of magnetic disaccommodation in amorphous ferromagnets. I. Experimental results (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4719-4723 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Systematic room-temperature measurements of the aftereffect of the ac magnetic permeability have been performed on a Fe81B13.5 Si3.5C2 amorphous ribbon in order to get detailed information about the nature of the atomic ordering processes responsible for the magnetic relaxation. The magnetic aftereffect related to 180° domain-wall motion has been measured by means of a specific technique allowing periodic domain-wall displacements to be induced between two fixed, neighboring equilibrium positions by applying a square-wave field of proper amplitude and frequency. In this way, the average direction of the magnetization vector is cyclically modified in all points where the studied directional ordering processes may occur. As a consequence, the kinetics of ordering is modified in a characteristic way, giving rise to relevant variations in the intensity of the magnetic aftereffect measured between fixed times (t1=2×10−3 s and t2=10−1 s), and in the value of the magnetic induction at the time t2. All measurements have been performed at constant applied field. The degree of reliability of this experimental technique has been analyzed in detail. The magnetic aftereffect, ΔB=B(t1)−B(t2), and the magnetic induction B(t2) have been measured as functions of the number of domain-wall cycles, and after removing the square-wave field for a variable time t*. The results of many independent measurements are reported and discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346152
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of stress anisotropy on hysteresis and Barkhausen noise in amorphous materials (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 4412-4414 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369801
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of microstructure on thermal relaxation in nanocrystalline soft magnetic materials (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7463-7465 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1355349
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  • 5
    Electronic Resource
    Electronic Resource
    Stochastic model for magnetic hysteresis (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 3253-3261 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model of ferromagnetic hysteresis is presented, in which the different microscopic magnetization processes are reduced to the motion of a single domain wall in a random energy landscape. The equivalent pinning field acting on the domain wall is assumed to be a space-dependent stochastic process described by a set of coupled Langevin-type equations. The model is inspired by the one proposed by Néel for the description of hysteresis in the Rayleigh region, but it is more general, as it predicts both the static and the dynamic hysteresis loops, as well as their fine structure (Barkhausen effect). The model properties were investigated by computer simulations. In the low field limit, the Rayleigh law is verified, with coefficients depending on the stochastic properties of the pinning field, whereas at high fields the loop behavior is dominated by demagnetizing fields. The results obtained for the energy losses show that the separation of losses into the hysteresis and the dynamic components is a general property of this model. Furthermore, we numerically verified that in our model there is a complete decoupling of the dissipation effects due to the presence of the pinning field (inner disorder) and to the dynamics of the domain wall. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371198
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  • 6
    Electronic Resource
    Electronic Resource
    Single Bloch wall dynamics in amorphous ribbons: A comparison between experimental and theoretical results (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 4117-4125 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A numerical approach is introduced to study the motion of a single bowed domain wall in an isotropic ferromagnetic lamination under general conditions of time dependence of the exciting magnetic field. A large set of numerical results concerning the behavior of Bloch walls in a magnetostrictive amorphous ribbon (Allied Signal Metglas 2605 SC), submitted to a sinusoidal field of varying amplitude and frequency is reported and discussed. The results are compared with the ones reported in the literature and obtained through different methods of calculation. The present approach allows one to get valuable information on the effect of wall bowing on the magnetic permeability, the so-called magnetic skin effect and the critical field which corresponds to a domain-wall instability resulting in wall multiplication. The peculiar behavior of the phase shift between wall oscillations at the lamination surface and within the lamination bulk appears to be very sensitive to the value of the wall's surface energy density σw, at least within an appropriate frequency domain, thereby suggesting a reliable method of measuring this quantity. Actual measurements performed on a Metglas 2605 SC ribbon by using a Kerr-effect optical technique are reported and compared with the theoretical predictions. When a tensile stress of about 500 MPa is applied to this highly magnetostrictive material to provide a regular pattern of straight domain walls aligned along the ribbon axis, a value of σw=1.7×10−3 J/m2 is found. This value is consistent with the one calculated from the magnetostriction and the exchange energy coefficient of Metglas 2605 SC, which is between 1.4×10−3 and 1.8×10−3 J/m2. Measurements of the behavior of the wall oscillation amplitude as a function of the field intensity are also reported and discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355992
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  • 7
    Electronic Resource
    Electronic Resource
    Relaxation of magnetoresistance and magnetization in granular Cu90Co10 obtained from rapidly quenched ribbons : The 6th joint magnetism and magnetic materials (MMM)−intermag conferenc (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6817-6819 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Bulk granular Cu90Co10 systems displaying a negative giant magnetoresistance (GMR) were produced by submitting melt-spun ribbons to conventional annealing and dc joule heating in order to induce diverse microstructures. Room-temperature GMR values up to 9% at 20 kOe were found in samples produced using both kinds of thermal treatments. An evolution from a superparamagnetic towards a ferromagnetic behavior has been observed in samples submitted to different heat treatments. A long-time, nearly logarithmic relaxation of the magnetic remanence has been measured after fast removal of a magnetic field of 10 kOe. The progressive randomization of the magnetic moments also gives rise to a corresponding increase in the zero-field electrical resistance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358139
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  • 8
    Electronic Resource
    Electronic Resource
    Evidence for a magnetic permeability relaxation of dissipative type in amorphous ferromagnetic alloys (1987)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 142-144 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A strong relaxation of the magnetic permeability is observed in amorphous ferromagnetic alloys when times shorter than 10−3 s after impulsive sample demagnetization are explored. This effect is not related to an activated ordering process. It is shown that the motion of domain walls is dominated, at the measuring frequency, by dissipative effects. As a consequence, the fast relaxation of the magnetic permeability is related to a change with time of the power dissipated by the system, rather than to a change of the restoring force acting on the walls, responsible instead for the conventional permeability aftereffect. A mechanism for the power dissipation change is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.98595
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  • 9
    Electronic Resource
    Electronic Resource
    Connection between hysteresis, Barkhausen noise, and microstructure in magnetic materials (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4768-4770 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373153
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  • 10
    Electronic Resource
    Electronic Resource
    Phenomenology and interpretation of the Barkhausen effect in ferromagnetic materials (invited) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5355-5360 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: After reviewing the main aspects of Barkhausen effect (BE) phenomenology and the principal theoretical models proposed for its interpretation, a new experimental and theoretical approach is presented. It is shown that definite progress in the comprehension of BE phenomenology is achieved by restricting BE experiments to the central part of the hysteresis loop, where BE behaves as a stationary stochastic process and domain wall motion is the dominant magnetization process. From the theoretical point of view, a critical reconsideration of literature results on domain wall dynamics is proposed, which leads to a Langevin equation for BE, whose solution provides definite analytic expressions for BE power spectrum and amplitude probability distribution. A comparison between the obtained theoretical predictions and typical experimental results is presented and discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342370
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