Effect of Nb addition on the structure and soft magnetic properties of melt-spun Co 69 Fe 7 Si 14 B 10 alloy D. Arvindha Babu a , J. Arout Chelvane a,n , Himalay Basumatary a , A.P. Srivastava b , T. Sahoo c , D. Akhtar a , M. Manivel Raja a a Defence Metallurgical Research Laboratory, Hyderabad, India b Bhabha Atomic Research Centre, Mumbai, India c Proof and Experimental Establishment, Balasore, India article info Article history: Received 1 October 2010 Received in revised form 14 May 2011 Accepted 16 May 2011 Available online 1 June 2011 Keywords: Rapid solidification Stripe domain M¨ ossbauer study Magnetoimpedance abstract Melt-spun ribbons of Co 69 Fe 7 Si 14x Nb x B 10 alloys with x ¼0, 2 and 4 have been prepared and characterized for structure and soft magnetic properties. Ribbons with x ¼0 and x ¼2 are found to be completely amorphous whereas the ribbon with x ¼4 contains irregular shaped faulted Co 2 Si orthorhombic phase with grain size of about 100 nm. Nb addition is found to decrease the degree of amorphicity and induce perpendicular anisotropy, deteriorating the soft magnetic and magnetoimpe- dance properties. & 2011 Elsevier B.V. All rights reserved. 1. Introduction Magnetoimpedance (MI) is the change in impedance of a soft ferromagnetic conductor on application of an external steady magnetic field. It has attracted considerable attention recently due to its potential application as magnetic field sensor. The essential criteria for a material to exhibit large MI are (i) it should be magnetically soft (ii) small electrical resistivity (iii) large saturation magnetization and (iv) small saturation magnetostric- tion [1]. The origin of MI lies in the changes of complex perme- ability of the material in the presence of an external magnetic field. In a soft ferromagnetic conductor, the magnetic permeabil- ity can change by orders of magnitude in the presence of an external magnetic field, which causes strong modifications in the internal fields, electrical current density and consequently on the material’s impedance. Amorphous and nanocrystalline alloys, e.g. Co-based amor- phous melt-spun ribbons, exhibit large magnetoimpedance effect as they possess excellent soft magnetic properties. Among the Co-based alloys, Co–Fe–Si–B alloy ribbons have been found to exhibit large MI [2,3]. Recently, we have studied the influence of quenching rate on the structure and soft magnetic properties of Co 69 Fe 7 Si 14 B 10 melt-spun alloy and found that higher quenching rate improves soft magnetic properties and MI [4]. Itoi and Inoue [5] have reported that the Nb addition enhances the glass forming ability and soft magnetic properties in Fe based amorphous alloys. Further, Nb addition improves the thermal stability of amorphous Fe–Si–B alloys at the expense of Curie temperature [6]. Phan et al. [7,8] reported that the substitution of Nb for B improves MI values in Co–Fe–Si–B alloy. It has also been reported [9] that the glass forming ability of Co-based amorphous wires can be improved by the addition of Nb, which in turn enhances the soft magnetic properties. Moreover, Nb substituted Co–Fe–Si–B alloys also find application in microwave power absorption [10]. Thus this study was therefore undertaken to study the effect of Nb addition on the structure and soft magnetic properties of melt-spun Co 69 Fe 7 Si 14 B 10 alloy. 2. Experimental Rapidly solidified ribbons (2 mm wide and 30 mm thick) of Co 69 Fe 7 Si 14x Nb x B 10 (x ¼ 0, 2 and 4) alloys were prepared using a vacuum melt spinner at a wheel speed of 47 m/s. Structural characterization was carried out using X-ray diffraction (XRD) employing CuK a radiation (Model: Philips-PW1830). A transmis- sion electron microscope (TEM) (FEI Tecnai-20 T) was used to observe the microstructural features. The samples were thinned from both sides of ribbon using precision ion polishing system (PIPS) by bombarding with Ar ion. Crystallization studies were Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/physb Physica B 0921-4526/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2011.05.033 n Corresponding author. Tel.: þ91 40 24586339; fax: 91 40 24340884. E-mail address: jarout@yahoo.com (J. Arout Chelvane). Physica B 406 (2011) 3243–3246