IEEE TRANSACTIONS ON MAGNETICS, VOL. 48, NO. 11, NOVEMBER 2012 4375 Magnetoimpedance Response in Co-Based Amorphous Ribbons Obtained Under the Action of a Magnetic Field L. González , J. Bonastre , T. Sánchez , J. D. Santos , M. L. Sánchez , A. Chizhik , L. Domínguez , M. Ipatov , V. Zhukova , A. Zhukov , J. González , J. J. Suñol , and B. Hernando Department of Physics, University of Oviedo, Oviedo 30007, Spain Department of Physics, University of Girona, Girona 17003, Spain Dept. Materials Physics, Faculty of Chemistry, University of the Basque Country, San Sebastian 20018, Spain Department of Applied Physics I, EPID, University of the Basque Country, San Sebastián 20018, Spain IKERBASQUE Foundation, Bilbao 48011, Spain Magnetoimpedance (MI) response in the frequency range of 10–1000 MHz of Co Fe Si B amorphous ribbons obtained by rapid solidification without and with a magnetic field of 56 kA/m applied in the transverse direction of the ribbon during the fabrication is reported. MI of the ribbon produced without magnetic field presents one-peak behaviour at low frequency ( MHz) emerging two-peaks above this frequency, while the two-peaks is present at all frequencies for the ribbon produced with magnetic field as a con- sequence of the transverse magnetic anisotropy induced during the fabrication process. The evolution of the maximum of MI with the axial magnetic field, ascribed to the anisotropy field, as a function of the frequency provides useful information on the ribbons magnetic inhomogeneity through their cross section. Index Terms—Soft amorphous magnetic alloy ribbons, induced magnetic anisotropy, magnetoimpedance effect. I. INTRODUCTION D URING almost two decades, a huge amount of re- search has been devoted to the so-called giant magne- toimpedance effect (GMI) in different soft magnetic materials (amorphous or nanocrystalline character) and geometry (conventional wires, glass-coated microwires, ribbons, mul- tilayers ) [1]–[6]. Such scientific research has dealt several aspects concerning the intrinsic magnetotransport properties (i.e.: frequency range, intensity of the effect, magnetic field to observe possible maximum, noise ) and, therefore, GMI is actually opening a new branch of research combining the micromagnetics of soft magnets with the classical electro- dynamics. Obviously, the different geometry leads to some differences in the GMI response like the frequency range and/or the magnetic field dependence of the impedance with one or two peaks behaviour or, it could be relevant in the shape of the peak, etc. In this context, it should be noted that the soft magnetic amor- phous ribbons result attractive because they can present a re- markable GMI response and, additionally, they can be easily produced with certain control of the cross-section parameters. Moreover, it is well established that a pre-requisite to achieve GMI effect in these materials is that concerning to the “trans- verse” magnetic susceptibility to the ribbon axis. This require- ment could be ascribed to the presence of macroscopic mag- netic anisotropy with its easy axis transverse to the longitudinal ribbon axis. The possibility to fabricate amorphous ribbons with trans- verse magnetic anisotropy has been recently reported in [7], Manuscript received February 28, 2012; revised April 26, 2012; accepted April 29, 2012. Date of current version October 19, 2012. Corresponding au- thor: J. González (e-mail: julianmaria.gonzalez@ehu.es). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMAG.2012.2198623 where we analyze the GMI response in Co Fe Ni Si B amorphous ribbons obtained by rapid solidification without and with a magnetic field of 56 kA/m applied in the transverse direc- tion of the ribbon during the fabrication. This route of fabrica- tion would induce a small transverse anisotropy without losing the amorphisation and good mechanical properties of the sam- ples with the benefits that such route avoiding the post-pro- cessing after the fabrication process following the conventional induction methods. In addition, this transverse anisotropy has associated non-axial components of the magnetic permeability necessary to observe the GMI effect. Previously, we have already reported on excellent magnetic softness and high GMI effect (low frequency range MHz) of this amorphous alloy ribbon [7]. In this work we have extended the frequency range of magnetoimpedance up to 1000 MHz, in order to get a deeper knowledge of this GMI response in low magnetostrictive amorphous alloys exhibiting ribbon geometry. II. EXPERIMENTAL DETAILS As has been afore mentioned, two kinds of ribbon were fabri- cated by the single melt-spinning technique one was quenched in the usual way (as-quenched sample) and other with an ap- plied magnetic field of 56 kA/m during the fabrication process (field-quenched sample). The ribbon was of 0.90 mm wide, 20 m thick and pieces of 1 cm length were cut to obtain the GMI experimental data. Hysteresis loops of the nearly-zero magne- tostriction amorphous ribbon of nominal composition Co Fe Si B was obtained at 12 Hz by a conventional induction method. The ribbon impedance was evaluated using a network ana- lyzer at frequencies 10–1000 MHz, as described elsewhere [4]. The impedance of the as-quenched and field-quenched pieces was determined with a N52 30A vector network analyzer through reflection coefficient measurement. The longitudinal magnetic field is produced by the currents running through the exciting coil, , where is the exciting coil 0018-9464/$31.00 © 2012 IEEE