Journal of the Korean Physical Society, Vol. 62, No. 10, May 2013, pp. 1382∼1387 GMI Effect of Amorphous Microwires with Enhanced Magnetic Softness A. Zhukov ∗ Dpto. de F´ ısica de Materiales, Fac. Qu´ ımicas, UPV/EHU, 20018, San Sebasti´ an, Spain and IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain M. Ipatov, A. Talaat and V. Zhukova Dpto. Fisica de Materiales, Fac. Quimicas, UPV/EHU, 20018 San Sebastian, Spain C. Garcia Bogazici Univ, Dept Phys, TR-34342 Istanbul, Turkey (Received 31 May 2012, in final form 7 August 2012) We present our results on studies of soft magnetic properties and GMI effect in thin microwires at elevated frequencies paying special attention to tailoring the GMI effect and achievement of high GMI ratio (∆Z/Z), high magnetic field sensitivity (dZ/dH) with low hysteretic behavior. We measured magnetic field dependence of real part, of the longitudinal wire impedance up to frequency, f , 4 GHz in Co-rich microwires. We observed that the GMI magnetic field dependence can be tailored either controlling magnetoelastic anisotropy of as-prepared microwires or by heat treatment. PACS numbers: 75.30.Gw, 75.50.Kj, 77.80.Dj Keywords: Glass-coated microwires, GMI effect, Soft magnetic materials DOI: 10.3938/jkps.62.1382 I. INTRODUCTION Amorphous soft magnetic materials continue playing important role in many technological applications [1]. Among different families of soft amorphous magnetic ma- terials, magnetically soft thin wires (with typical diame- ters from 1 to 120 μm) attract considerable interest ow- ing to unusual magnetic properties exhibiting by amor- phous ferromagnetic wires such as magnetic bistability and giant magneto-impedance, GMI, effect [1–3]. These properties are especially attractive for the magnetic sen- sor applications. One of the recent tendencies in the field of magnetic sensor applications is their miniaturization. Therefore reduction of diameters of magnetically soft wires keep- ing soft magnetic properties is one of the prioritary tasks in this field of applied magnetism. Therefore, studies of magnetically soft thin wires attract considerable at- tention [4–7]. The advantage of the Taylor- Ulitovsky method allowing the fabrication of glass-coated metallic microwires consists of controllable fabrication of long (up to few km long continuous microwire) and homogeneous thin composite wires. After certain progress on fabrication, characteriza- tion and design of soft magnetic properties and gi- * E-mail: arkadi.joukov@ehu.es ant magneto-impedance, GMI, effect of amorphous mi- crowires at the laboratory level [7], industrial applica- tions of thin wires with GMI effect for low magnetic field detection have been reported [6,8]. As regarding applications in magnetic sensors, afore- mentioned GMI effect, consisting of large change of the impedance of magnetically soft conductor under effect of applied magnetic field considered the most promising [6–10]. The GMI effect has been successfully explained in the terms of classical electrodynamics through the in- fluence of magnetic field on penetration depth with the skin effect of the electrical current flowing through the magnetically soft conductor [9,10]. Cylindrical shape and high circumferential perme- ability observed in amorphous wires are quite favor- able for achievement of high GMI effect [4, 7–10]. In fact, highest GMI effect and best soft magnetic properties are observed for nearly-zero magnetostrictive compositions. For the most attractive Co-Fe- based (Co x Fe 1-x ) 75 Si 15 B 10 system the magnetostriction con- stant, λ s , changes with x from –5 × 10 -6 at x = 1, to λ s ≈ 35 × 10 -6 at x ≈ 0.2, achieving vanishing value at Co/Fe ratio about 70/5 [11]. It is worth mentioning, that the magnetic field depen- dence of the impedance of magnetic conductor is mainly determined by the type of magnetic anisotropy. Thus the circumferential anisotropy leads to the observation of the -1382-