Materials Science and Engineering A 375–377 (2004) 1015–1018 Connection between magnetic and magnetotransport properties in Co-based rapidly solidiﬁed alloys C. Appino, C. Beatrice, M. Coisson, P. Tiberto, F. Vinai ∗ Istituto Elettrotecnico Nazionale Galileo Ferraris and INFM, Strada delle Cacce 91, I-10135 Torino, Italy Abstract The inﬂuence of a macroscopic uniaxial anisotropy, induced by ﬁeld annealing, on the magneto-impedance effect (GMI) behaviour in Co 71 Fe 4 Si 10 B 15 amorphous ribbons has been studied. Two kinds of samples, showing longitudinal or transverse domain pattern, have been obtained by means of suitable thermomagnetic treatments. The magneto-impedance features were investigated in the two specimens, and in particular a linear dependence of the GMI response, as a function of the distance between the electrical contacts, has been pointed out in both cases. © 2003 Elsevier B.V. All rights reserved. Keywords: Amorphous systems; Magneto-impedance; Domain pattern 1. Introduction The recent discovery in the last decade of magneto- impedance effect (GMI) in soft magnetic materials has raised a considerable interest among the scientiﬁc com- munity due to its technological application as sensitive magnetic ﬁeld sensors [1,2]. This effect, consisting in a strong impedance variation in presence of an external static magnetic ﬁeld, has an electromagnetic origin and is strictly related to the frequency-dependent penetration depth δ in the magnetic conductor [3]. By considering the general expres- sion for the penetration depth δ = (1/µσπf) 0.5 , where σ is the sample electrical conductivity and f the electrical current frequency, it can be noted that the magnetic permeability µ (transversal or circular in the case of ribbons and wires, respectively) plays a key role in the magneto-impedance re- sponse. As a consequence, GMI turns out to depend on the domain structure and consequently on induced anisotropy [4]. Recently, to point out the magneto-impedance depen- dence on the geometrical dimension, the inﬂuence of both sample length and distance between electrical contacts on the GMI have been carefully studied in Fe–Cr–Si–B–Cu– Nb ultrasoft magnetic wires [5]. These specimens display a central axial domain surrounded by a transverse one, and ∗ Corresponding author. Tel.: +39-011-391-9857; fax: +39-011-391-9834. E-mail address: vinai@ien.it (F. Vinai). closure domains near the end, leading to a bistable magneti- sation behaviour. The connection between the presence of closure structures and the reduction of magneto-impedance response has been put in evidence. In this work, longitudinal and transverse magnetic domain patterns have been tailored in nearly zero magnetostrictive Co 71 Fe 4 Si 10 B 15 melt-spun amorphous ribbons by means of performing suitable magnetic annealing. In this way, the effect of induced magnetic anisotropy on the magneto- impedance response has been ruled out. Furthermore, the dependence of GMI intensity on the distance between the electrical contacts has been investigated and correlated to the local domain structure induced by annealing. 2. Experimental A Co 71 Fe 4 Si 10 B 15 ribbon (thickness ∼ = 20 m; width 10 mm; length 28 cm) has been rapidly solidiﬁed by means of the planar ﬂow casting technique. This composition is characterised by a nearly zero magnetostriction and there- fore thermo-magnetic treatments are an effective tool in order to induce an uniaxial macroscopic anisotropy and con- sequently to obtain samples with parallel and well deﬁned domain walls. To relieve the quenched-in stresses, all stud- ied samples cut from the same ribbon have been previously furnace annealed (T a = 300 ◦ C for 1 h). This treatment, performed by applying a saturating magnetic ﬁeld, directed 0921-5093/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2003.10.033