Materials Science and Engineering A 375–377 (2004) 1036–1039 Effect of thermal treatments on the high-frequency magnetic permeability of glass-covered Co 83.2 Mn 17.6 Si 5.9 B 3.3 wires M. Coisson a,b , P. Tiberto a,b , F. Vinai a,b,∗ , S.N. Kane c,1 a IEN Galileo Ferraris, Strada delle Cacce 91, 10135 Torino, Italy b INFM, UdR TO-Poli, Torino, Italy c SATIE UMR CNRS, Ecole Normale Supérieure de Cachan, 61 Avenue de Président Wilson, 94235 Cachan, France Abstract Samples of glass-covered Co 83.2 Mn 17.6 Si 5.9 B 3.3 wires have been used as inner conductors of a section of coaxial line, whose reflection parameter has been measured by means of a network analyser. From high-frequency magneto-impedance data it is possible to extract information about the magnetic permeability of the sample, as a function of frequency or of an externally applied static longitudinal magnetic field. Curves of relative circular magnetic permeabilities are reported for as-prepared, conventionally annealed and Joule-heated samples. Features of the permeability curves displaying a ferromagnetic-resonance-like behaviour are shown and discussed. © 2003 Elsevier B.V. All rights reserved. Keywords: Magneto-impedance; Magnetic permeability; Coaxial transmission lines; Amorphous glass-covered wires 1. Introduction In the last years, the quest for increasing miniaturisation of devices eventually led to the development of materials working in the GHz region. To this aim, rapidly solidified alloys, either in wire or ribbon form, have been extensively studied because of their theoretical and technological inter- est [1]. In particular, Giant magneto-impedance (GMI) and magnetic permeability are interesting properties that have been widely investigated. Many experimental techniques have been developed in order to characterise such magnetic systems up to the microwave frequency region; among the others, methods using coaxial lines are particularly suit- able for the characterisation of wires and ribbons [2,3]. In this paper, samples of glass-covered Co 83.2 Mn 17.6 Si 5.9 B 3.3 wires have been used as inner conductors of a section of a coaxial line, whose reflection parameter S 11 has been measured by means of a vectorial network analyser. The characteristic impedance of the line containing the sample can be calculated [3], and if repeated measurements are per- formed under different applied longitudinal magnetic fields, ∗ Corresponding author. E-mail address: vinai@ien.it (F. Vinai). 1 On leave from School of Physics, D.A. University, Khandwa Road, Indore 452017, India. high-frequency GMI characterisations can be made. Several samples have been examined, both as produced and submit- ted to different thermal treatments (conventional annealing in furnace and dc Joule heating in vacuum). In this work, the analytical procedure to obtain the relative circular magnetic permeability from characteristic impedance measurements is discussed in detail. All samples show a variation of the circular magnetic permeability with frequency and applied field. Ferromagnetic resonance-like features of the perme- ability curves as a function of frequency at different fields are observed for all samples. 2. Experimental Glass-covered amorphous wires (metallic diameter ∼20 mm, glass coating thickness ∼5 mm) of nominal atomic composition Co 83.2 Mn 17.6 Si 5.9 B 3.3 have been sub- mitted to conventional annealing in furnace (T a = 100, 125 and 200 ◦ C for 30 min) and to dc Joule-heating in vacuum (I a = 2, 3 and 4 mA for 3600 s [4]). The amorphicity of the samples before annealing has been tested by X-ray diffraction [5]. Annealing temperatures and currents ensure that quenched-in stresses are relieved without inducing nanocrystallisation [4] (Joule-heated samples are submitted to a self-induced circular field annealing, possibly enhancing 0921-5093/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2003.10.009