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Frequency-Dependence of Relative Permeability in Steel

“…The phenomenon may therefore be expected to be disorder-dependent, related to the density of pinning sites in the material, which in turn may be related to the percent carbon content in steel, for example. Indeed, relaxation in µ has not been observed in similar experiments on spring steel [1] and an independent study has shown a difference in behavior between iron and quenched steel [3], as shown in Figures 9 and 10. Surface condition and processing history of the sample may also play a role, since both of these influence the density and nature of domain-wall pinning sites.…”

“…Possible mechanisms responsible for this effect include phase lag in the motion of magnetic domain walls, with respect to the applied alternating current injected into the plate [2], or the presence of a surface region in which the material structure and its electromagnetic properties have been modified, compared with the bulk, for example by processing methods such as cold-rolling. The need for a complex, frequency-dependent magnetic permeability has also been recognized in studies on various ferromagnetic metal plates subjected to a homogenous time-harmonic magnetic field, with impedance measurements made by a pick-up coil wrapped around the specimen [3].…”

“…Real and imaginary parts of complex permeability as a function of frequency for measurements on iron and quenched steel. Data is taken from reference[3].…”