Multilayer models on the surface conditions of ferromagnetic metals

Tai, Cheng-Chi; Liu, Yin-Hsiung
May 2000
AIP Conference Proceedings;2000, Vol. 509 Issue 1, p1605
Academic Journal
Many ferromagnetic metals have either by design or happenstance a very thin surface layer of reduced magnetic permeability. Such a layer might occur intrinsically or be induced by surface treatments such as case hardening, shot peening, or surface alloying. We study the frequency-dependent impedance of a small air-cored coil of wire placed flat upon ferromagnetic metal plates. The impedance changes for Ni and Fe could not be fit to the half-space model for any values of σ and μ, but were consistent with a model that assumes a thin (several microns) surface layer. We do not believe that a single-layer model is a satisfactory explanation of the observed data. It is likely that the permeability varies continuously with depth in the near-surface region. Hence, it is possible a multilayer model might yield a better representation of the data with a layer depth closer to that observed. In this study, we show that the multilayer model improves the agreement between the measured data and the approximate analytic fitting form. This work will pave the way to a comprehensive understanding of the profile in the near-surface region of ferromagnetic metals. © 2000 American Institute of Physics.


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