Bias-current eect on giant magnetoimpedance in Co-based amorphous microwire Kwang Seok Byon a , Seong-Cho Yu a, * , Cheol Gi Kim b , Manuel V azquez c a Department of Physics, Chungbuk National University, Cheongju 361-763, Republic of Korea b Department of Phys. & Adv. Mater., Sun Moon University, Chung-nam 336-840, Republic of Korea c Instituto de Ciencia de Materiales, CSIC, 28049 Cantoblanco, Madrid, Spain Abstract The giant magnetoimpedance GMI) eect has been measured in Co 83:2 B 3:3 Si 5:9 Mn 7:6 amorphous microwire as a function of direct current dc)-biased current and measuring frequency, f. The GMI pro®le has a single peak for f 6 5 MHz,andtwopeaksathigherfrequency.ThemaximumGMIratioincreasescontinuouslywithfrequencyupto45% at 10 MHz. The in¯uence of superimposed dc biasing is shown to result in asymmetrical GMI as well as in a shift of the axial hysteresis loop. Both eects are interpreted in terms of the relative contribution of domain wall and rotational processes to the transverse susceptibility. Ó 2001 Elsevier Science B.V. All rights reserved. PACS: 75.60.ch; 75.20.M 1. Introduction Recently, several works on the giant magne- toimpedance GMI) eect have been reported on Co-based wires and microwires with a ®nal aim of developing sensitive magnetic sensors [1,2]. GMI eects originate in the skin eect as a consequence ofthechangesinthepenetrationdepthinducedby the static applied ®eld through modi®cation of the transverse susceptibility [3±5]. Recent experiments have been directed at improvement of the GMI ratio and its ®eld sensitivity by modifying an- nealing conditions, bias ®eld or current, and applied stress [5±9]. These magnetically soft amorphous wires consist of two main regions of domains,acoreandanoutershell.Suchadomain structure is determined by distribution of the magnetoelasticanisotropyarisingfromthestresses quenched-in by thermal gradient during the fab- rication process [4]. In Co-based wires, the inner core domains exhibit an axial easy magnetization direction, and for the outer shell domains the easy direction is a circular one [10]. The GMI is determined by the modi®cation of the circumferential permeability by the static magnetic ®eld. In some technological applications, an asymmetric magnetoimpedance is required to improve linearity and ®eld sensitivity [11]. The asymmetrical GMI pro®le is present when the combination of two kinds of uniaxial and unidi- rectional anisotropies exists in a material [7]. In this work, GMI eect and axial M ±H hys- teresis loops are reported in a non-magnetostric- tive Co-base microwire as a function of the bias current.Resultsarediscussedintermsofmagnetic Journal of Non-Crystalline Solids 287 2001) 339±343 www.elsevier.com/locate/jnoncrysol * Corresponding author. Tel.: +82-431 261 2269; fax: +82-431 275 6416. E-mail address: scyu@cbucc.chungbuk.ac.kr S.-C. Yu). 0022-3093/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0022-309301)00579-8