Circumferential permeability in nonmagnetostrictive amorphous wires
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Circumferential permeability in nonmagnetostrictive amorphous wires M. L. Sancheza) Departamento de Fisica, Universidad de Oviedo, Calvo Sotelo s/n, 33007-Oviedo, Spain
R. Valenzuela,b) M. Vazquez, and A. Hernando Instituto de Magnetismo Aplicado, UCM, and Instituto de Ciencia de Materiales, CSIC, P.O. Box, 155, 28230 Las Rozas, Madrid, Spain (Received 17 July 1995; accepted 18 June 1996)
Real and imaginary components of the impedance response on Co68.1 Fe4.4 B15 Si12.5 amorphous as-cast wires were measured in the 100 Hz–100 kHz frequency range and 0.05–30 mA (RMS) current amplitude, at axial dc fields of 0 and 4800 Aym. From these data, plots of circumferential complex permeability as a function of circular field, as well as magnetization curves, were derived. Results are analyzed in terms equivalent circuits, which allows a resolution of domain wall and rotational contributions to the circumferential magnetization processes. I. INTRODUCTION
Recently, giant magnetoimpedance (GMI) phenomena have attracted a great deal of interest because of their potential use in technological applications such as sensors or magnetic heads.1 GMI has already been studied in amorphous2–4 and nanocrystalline wires5 and ribbons.6,7 This phenomenon consists essentially in large variations of the material’s impedance (subjected to a longitudinal ac current), when an axial dc magnetic field is applied. The GMI effect is strongest in the case of amorphous wires with small, negative magnetostriction constant, prepared by the in-rotating-water quenching technology.8 Their structure can be schematically described by an inner core axially magnetized, and an outer shell with circumferentially oriented domains. When l is very small, the core has a nearly axial multidomain structure, and the domains in the outer shell are not perfectly circumferential.9 The impedance response depends on the interactions between the outer shell domains of the wire and the circular field generated by the high frequency current. The application of an axial dc field decreases the outer domains (eventually suppressing them for fields sufficiently strong), leading to a large decrease in the impedance response; this is the basis of GMI. The impedance dependence with axial field is stronger at frequencies in the 100 kHz –1 MHz range. At these frequencies, skin-depth effects play an important role in the wire magnetization processes, leading to further complexity. GMI has been phenomenologically explained by using classical electrodynamics.2,6 Recently, an alternative approach has been proposed,10 a) On b)
sabbatical leave from the National University of Mexico. Address all correspondence to this author.
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http://journals.cambridge.org
J. Mater. Res., Vol. 11, No. 10, Oct 1996
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based on the modeling of GMI by means of equivalent circuits. A direct association of equivalent circuit elements with physical parameters of the material allowed a resolution of the magnetization processes.11 To our kn
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