Microwires coated by glass: A new family of soft and hard magnetic materials
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J. Gonza´lez Departamento de Fı´sica de Materiales, Facultad de Ciencias Quı´micas, P.O. Box 1072, 20080 San Sebastia´n, Spain
J.M. Blanco Departamento de Fı´sica Aplicada I, Escuela Universitaria de Ingenierı´a Te´cnica Industrial, 20011 San Sebastia´n, Spain
M. Va´zquez Instituto de Magnestismo Aplicado, Red Nacional de Ferrocarriles Espan˜olas-Universidad Complutense de Madrid (RENFE-UCM), and Instituto de Ciencia de Materiales, Consejo Superor de Investigaciones Cientificas (CSIC), P.O. Box 155, 28230 Las Rozas, Madrid, Spain
V. Larin AmoTec, Kishinev, B-d Dacia 15 ap. 78, Moldova (Received 21 June 1999; accepted 7 July 2000)
The Taylor–Ulitovski technique was employed for fabrication of tiny ferromagnetic amorphous and nanocrystalline metallic wires covered by an insulating glass coating with magnetic properties of great technological interest. A single and large Barkhausen jump was observed for microwires with positive magnetostriction. Negative magnetostriction microwires exhibited almost unhysteretic behavior with an easy axis transverse to the wire axis. Enhanced magnetic softness (initial permeability, ι, up to 14000) and giant magneto impedance (GMI) effect (up to 140% at 10 MHz) was observed in amorphous CoMnSiB microwires with nearly zero magnetostriction after adequate heat treatment. Large sensitivity of GMI and magnetic characteristics on external tensile stresses was observed. Upon heat treatment, FeSiBCuNb amorphous microwires devitrificated into a nanocrystalline structure with enhanced magnetic softness. The magnetic bistability was observed even after the second crystallization process (increase of switching field by more than 2 orders of magnitude up to 5.5 kA/m). Hard magnetic materials were obtained as a result of decomposition of metastable phases in Co–Ni–Cu and Fe–Ni–Cu microwires fabricated by Taylor–Ulitovski technique when the coercivity increased up to 60 kA/m. A magnetic sensor based on the magnetic bistability was designed.
I. INTRODUCTION
The study of the magnetic properties of ferromagnetic wires obtained by the in-rotating-water quenching technique with a typical diameter of around 120 m has become a classic topic of applied magnetism owing to their very particular magnetization properties. Indeed, wires of magnetostrictive compositions show a single and quite large Barkhausen jump between two stable remanent states (so-called magnetic bistability, MB).1–3 It is spontaneously observed in magnetostrictive Fe and Co based wires with a length larger than a critical value of around 7 cm. Besides, the giant magnetoimpedance (GMI) effect has been observed and intensively studied in the last few years.4,5 J. Mater. Res., Vol. 15, No. 10, Oct 2000
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An alternative technology, the Taylor–Ulitovsky method for fabrication of tiny metallic microwires coated by insulating glass, has been known since the fifties.6 Technological aspects of such a method, such as the thermodynamic aspects of formation of the composite microwire and it
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