Tailoring of Magnetic Properties of Glass coated Microwires
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Tailoring of Magnetic Properties of Glass coated Microwires A.P. Zhukov1,2, J. González3 V. Zhukova3 and J.M. Blanco4 1
Donostia International Physics Centre, P. M. de Lardizabal 4, 20018 San Sebastián, Spain 2 "TAMag" S.L., C/ José Abascal 53, Madrid, Spain 3 Dept. Material Physics, Chemistry Faculty, P.O. Box 1072, 20080 San Sebastián, Spain 4 Dept. Appl. Phys. I, EUITI, UPV/EHU, Avda Felipe IV 1B, 20011, San Sebastián (Spain). ABSTRACT The magnetic behaviour of the glass-covered metallic microwires with a wide compositional range of composition with soft and hard magnetic character is presented. The effect of conventional furnace and dc current annealing under dc axial magnetic field or without it as well as of a chemical etching on the magnetic properties of Co and Fe-based glass coated microwires has been studied. Such treatments modify the magnetic parameters. In particular, annealing under applied magnetic field (field annealing) can improve significantly such magnetic parameters as permeability. Such phenomenology can be interpreted considering the noticeable magnetic anisotropy induced by the combined effects of the magnetic field and strong internal stresses arising from the coating. Giant magnetoimpedance (GMI) effect was observed in nearly-zero magnetostrictive amorphous microwires. Upon careful heat treatment, FeCuNbSiB amorphous microwires devitrificate into nanocrystalline structure with large variety of magnetic parameters. Hard magnetic materials with coercivity up to 800 Oe were obtained as a result of decomposition of metastable phases in Co-Ni-Cu microwires as well as after crystallization process of FeCuNbSiB amorphous microwires. 1. INTRODUCTION Studies of ferromagnetic amorphous wires obtained by in-rotating-water quenching technique with a typical diameter of around 120 µm has become a classic topic of applied magnetism owing to their very particular magnetization properties. Large Barkhausen jump between two stable remanent states (so-called magnetic bistability, MB) and Giant Magneto-Impedance (GMI) effect have been observed and intensively studied in the last few years [1]. An alternative technology, the Taylor-Ulitovsky method, was recently employed to produce continuous microwire (0.4 Km/min) with a metallic nucleus (typically from about l µm to 20 µm in diameter) covered by insulating Pyrex-type glass coating sheath (with the thickness of 1- 10 µm). A number of outstanding magnetic properties, such as magnetic bistability, enhanced magnetic softness and GMI effect (up to 130%) have been found recently in such microwires [2-5]. The magnetic properties of microwires are correlated with their microstructure, composition and internal stresses originated from the difference of thermal expansion coefficients of the metal and the glass. Consequently, the magnetic properties could be improved by adequate treatment: heat treatment or chemical etching of the glass coating or by the selection of adequate chemical composition of the metallic nucleus. The aim of this paper is to present novel resul
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