C. Beatrice

Domain‐wall dynamics and Barkhausen effect in metallic ferromagnetic materials. I. Theory

The Barkhausen effect (BE) in metallic ferromagnetic systems is theoretically investigated by a Langevin description of the stochastic motion of a domain wall in a randomly perturbed medium. BE statistical properties are calculated from approximate analytical solutions of the Fokker–Planck equation associated with the Langevin model, and from computer simulations of domain‐wall motion. It is predicted that the amplitude probability distribution P0(Φ) of the B flux rate Φ should obey the equation P0(Φ)∝Φc−1 exp(−cΦ/〈Φ〉), with c>0. This result implies scaling properties in the intermittent behavior of BE at low magnetization rates, which are described in terms of a fractal structure of fractal dimension D<1. Analytical expressions for the B power spectrum are also derived. Finally, the extension of the theory to the case where many domain walls participate in the magnetization process is discussed.

Domain-wall dynamics and Barkhausen effect in metallic ferromagnetic materials. II, Experiments

Barkhausen effect (BE) phenomenology in iron‐based ferromagnetic alloys is investigated by a proper experimental method, in which BE experiments are restricted to the central part of the hysteresis loop, and the amplitude probability distribution, P0(Φ), and power spectrum, F(ω), of the B flux rate Φ are measured under controlled values of the magnetization rate I and differential permeability μ. It is found that all of the experimental data are approximately consistent with the law P0(Φ)∝Φc−1 exp(−cΦ/〈Φ〉), where all dependencies on I and μ are described by the single dimensionless parameter c>0. Also the parameters describing the shape of F(ω) are found to obey remarkably simple and general laws of dependence on I and μ. The experimental results are interpreted by means of the Langevin theory of domain‐wall dynamics proposed in a companion paper. The theory is in good agreement with experiments, and permits one to reduce the basic aspects of BE phenomenology to the behavior of two parameters ...

Connection between hysteresis and thermal relaxation in magnetic materials

The connection between hysteresis and thermal relaxation in magnetic materials is studied from both the experimental and the theoretical viewpoint. Hysteresis and viscosity effects are measured in Finemet-type nanocrystalline materials above the Curie temperature of the amorphous phase, where the system consists of ferromagnetic nanograins imbedded in a paramagnetic matrix. The hysteresis loop dependence on field rate, the magnetization time decay at different constant fields, and the magnetization curve shape after field reversal are all consistent with a single value of the fluctuation field

Phenomenology and interpretation of the Barkhausen effect in ferromagnetic materials (invited)

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Giant magnetoimpedance and induced anisotropy in joule-heated and conventionally annealed Co-based amorphous materials

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Suppression of the magnetic‐permeability relaxation in nanocrystalline Fe73.5Cu1Nb3Si13.5B9

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Permeability and losses in ferrites from dc to the microwave regime

In addition, it is shown that all data collapse onto a single curve

Dynamic effects driven by thermal activation in the magnetization of nanocrystalline soft magnetic materials

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Evidence for a magnetic permeability relaxation of dissipative type in amorphous ferromagnetic alloys

when magnetization is plotted as a function of a properly defined field

Hysteresis properties of conventionally annealed and Joule-heated nanocrystalline Fe73.5Cu1Nb3Si13.5B9 alloys

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