Journal of Alloys and Compounds 420 (2006) 9–14 Giant magnetoimpedance effect in electroplated CoNiFe/Cu wires with varying Ni, Fe and Co content F.E. Atalay ∗ , H. Kaya, S. Atalay Inonu University, Science and Art Faculty, Department of Physics, 44069 Malatya, Turkey Received 17 September 2005; received in revised form 7 October 2005; accepted 18 October 2005 Available online 16 November 2005 Abstract Giant magnetoimpedance (GMI) behaviour has been studied for wires consisting of an 8.82–13.75 m thick magnetic layer containing either Co 20.77 Ni 61.74 Fe 17.49 , Co 18.21 Ni 41.20 Fe 40.59 , Co 18.97 Ni 49.60 Fe 31.43 , Co 46.01 Ni 39.87 Fe 14.12 or Co 33.67 Ni 51.44 Fe 14.89 . These magnetic layers were electroplated onto a 50 m diameter Cu non-magnetic wire. A large and sensitive GMI effect (about a 257% magnetoimpedance ratio) with nearly no hysteresis has been found in Co 18.97 Ni 49.60 Fe 31.43 wire at a 90 kHz ac driving current. Scanning electron microscopy (SEM) images showed that samples have globular and crack-free deposits with a grain size that varies between 3.06 and 9.17 m. © 2005 Elsevier B.V. All rights reserved. PACS: 75.70.Ak; 75.47.Np Keywords: Magnetoimpedance effect; Electroplate 1. Introduction The giant magnetoimpedance (GMI) effect in amorphous wires has been a subject of increasing interest. The GMI effect can be defined as the change of impedance of a soft magnetic element carrying a high frequency current, as a function of the external dc magnetic field [1–4]. Investigations of the GMI effect have been quickly extended to ribbons and films [5–15]. Recently, the GMI effect has been observed in electroplated composite wires consisting of a highly conductive inner core and a magnetically soft outer shell, which plays an important role in determining the magnitude of the GMI effect. The electrodepo- sition of a magnetic layer on the conductive inner core shows some advantages over the rapidly quenched amorphous materi- als. The rapid quenching process induces a considerable amount of internal stresses, which can affect the magnetic characteristics even in low magnetostrictive alloys. The importance of these internal stresses can be estimated in order of magnitude, but cannot be precisely controlled during the fabrication procedure [9]. The electrodeposited materials usually show high repro- ∗ Corresponding author. Tel.: +90 422 3410018; fax: +90 422 3410037. E-mail address: fatalay@inonu.edu.tr (F.E. Atalay). ducibility with respect to their properties, including magnetic properties. As the magnetic properties are essential for some sensor applications, this reproducibility is highly desirable. Recently, the GMI effect was studied on a nickel–iron (NiFe) layer that was electrodeposited over copper (Cu) wires [15]. It was reported that the magnitude of the GMI effect in NiFe/Cu varies between 40 and 750% depending on the Cu wire diame- ter, electrodeposition parameters such as the pH of the solution, current density, plating time and composition of the solution [15–17]. Kurlyandskaya and co-workers [11–14] have studied the GMI effect on Co 6 Fe 20 Ni 74 plated wire; under optimum conditions, a maximum GMI of 50% was reported for this wire. They have also measured the non-linear GMI effect on this com- position and found a maximum GMI of 800% under optimum conditions. Gibbs et al. [18] stated that the commercial magnetoresistive sensors that are based on anisotropic (AMR) or GMR are currently available in the market-place (AMR, Philips and Honeywell; GMR, NVE and Siemens). The spin-valve is the current sensor of choice in data storage heads. At present, there are no major commercial products that use the GMI effect. We therefore, believe that the GMI effect, particularly in thin-film NiFe and CoNiFe samples, still needs detailed investigation. Until now, there have been no reports on the GMI effect in 0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2005.10.022