research papers 240 https://doi.org/10.1107/S1600577520015131 J. Synchrotron Rad. (2021). 28, 240–246 Received 22 July 2020 Accepted 13 November 2020 Edited by G. Gru ¨ bel, HASYLAB at DESY, Germany Keywords: Co-rich glassy ribbons; EXAFS; coordination number; thermodynamic parameter. Supporting information: this article has supporting information at journals.iucr.org/s Local structure investigation of Co–Fe–Si–B ribbons by extended X-ray absorption fine-structure spectroscopy A. A. Deshmukh, a,b * A. P. Srivastava, c J. P. Singh, d Manish Kumar, d K. H. Chae, e K. Asokan f and U. A. Palikundwar a * a X-ray Research Laboratory, Department of Physics, Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur, MS 440033, India, b Department of Metallurgical and Materials Engineering, National Institute of Technology, Rourkela, Odisha 769008, India, c Mechanical Metallurgy Division, Bhabha Atomic Research Centre, Mumbai, MS 400085, India, d Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang 37673, Republic of Korea, e Advanced Analysis Center, Korea Institute of Science and Technology, Seoul 2792, Republic of Korea, and f Inter-University Accelerator Centre (IUAC), Aruna Asaf Ali Marg, New Delhi 110 067, India. *Correspondence e-mail: akdeshmukh9@gmail.com, uapali@yahoo.com In the present work, extended X-ray absorption fine-structure (EXAFS) investigations of Co 69 Fe x Si 21–x B 10 (x = 3, 5, 7) glassy ribbons were performed at the Co K-edge. The magnitude of the first peak of the Fourier transforms of the EXAFS signals is found to increase monotonically with increasing Si concentrations indicating the formation of the localized ordered structure at the atomic scale. The Co–Si coordination number (CN) increases at the expense of the CN of Co/Fe. Smaller interatomic distances are observed in the glassy phase compared with that in the crystalline phase which promotes the stability of the glassy phase. Calculations of the thermodynamic parameter (P HSS ), cohesive energy (E C ) and the atomic radius difference () parameter show that the alloy composition Co 69 Fe 3 Si 18 B 10 has a good glass-forming ability (GFA) with the highest CN of Si compared with other compositions. A linear correlation of CN with that of the GFA parameter (P HSS ) exists and the CN also plays a crucial role in the GFA of the glassy alloys. This parameter should be considered in developing different GFA criteria. 1. Introduction Cobalt (Co) based glassy alloys were found to have low magnetostriction and low coercivity, high initial and maximal permeability (Babilas et al. , 2012; Vojtanik, 2006; Zakharenko et al., 2006; Bednarcik et al., 2004). These glassy alloys have applications in various fields which include magnetic wires, magnetic sensors, band-pass filters and magnetic shielding (Babilas et al. , 2012; Vojtanik, 2006; Zakharenko et al. , 2006; Bednarcik et al., 2004). Earlier, numerous Co-based ternary alloys such as Co–Si–B (Kulik et al., 1984; Hagiwara et al., 1982; Baczewski et al., 1984; Barquin et al., 1994; Inoue et al. , 1995; Wexler & Emr, 1997; Wang et al., 2007), Co–Ta–B (Yu et al., 2014), quaternary alloys such as Co–Fe–Si–B (Babilas et al., 2012; Bednarcik et al., 2004; Kulik et al., 1984; Liu et al., 2012; Janotova ´ et al., 2014; Srivastava et al., 2016), Co–Fe–B– Nb (Gupta et al., 2012), Co–Fe–Ta–B (Taghvaei & Eckert, 2016), quinary alloys such as Co–Fe–Si–B–Nb (Janotova ´ et al., 2014; Sidorov et al. , 2014; Man et al., 2010; Dong et al., 2012; Liao et al. , 2019), Co–Fe–Si–B–Ni (Srivastava et al., 2012) and hexenary alloys such as Co–Fe–Si–B–Nb–Ga (Hosko et al. , 2012) were investigated for different magnetic and mechanical properties. Nevertheless, the glass-forming ability (GFA) of Co-based bulk metallic glasses (BMGs) was found to be ISSN 1600-5775 # 2021 International Union of Crystallography