Effect of replacing B by Zr in amorphous Co-Fe-Si-B soft magnetic alloys
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Wasif Hussain Khan National Institute of Technology, Raipur, Chattisgarh 492 010, India
Jeyaramane Arout Chelvane Defence Metallurgical Research Laboratory, Hyderabad 500 058, India
Trilochan Sahoo Proof and Experimental Establishment, Balasore, Orissa 756 025, India
Dilshad Akhtar Defence Metallurgical Research Laboratory, Hyderabad 500 058, India (Received 31 August 2011; accepted 23 January 2012)
Amorphous ribbons of Co69Fe7Si14B10-xZrx (x 5 0, 2.5, 5, 7.5 and 10) alloys have been prepared and their structure, soft magnetic and magnetoimpedance (MI) properties have been investigated. Glass forming ability (GFA) of these alloys was calculated using GFA parameter (a 5 Tx /Tl) and verified by experimental results. Saturation magnetization of the amorphous ribbon decreases on replacement of B by Zr which reveals Zr has more pronounced effect in decreasing saturation magnetization. However, improvement of other soft magnetic properties (coercivity and permeability) leads to considerable increase in MI properties. Annealing leads to crystallization of Co2Si, Co2B, Co2Zr and CoSi phases causing deterioration of soft magnetic and MI properties due to the magnetic hardness of the secondary phase which arises due to the presence of magnetocrystalline anisotropy.
I. INTRODUCTION
In recent years, amorphous Co-Fe-Si-B alloy ribbons have attracted considerable attention due to its excellent soft magnetic and magnetoimpedance (MI) properties.1,2 Soft magnetic properties of these alloys are attributed to almost zero magnetocrystalline anisotropy and very low saturation magnetostriction.1 Further, these alloys possess high transverse permeability through transverse domain structure. When magnetic field is applied, the transverse permeability decreases by many orders of magnitude causing increase in skin depth which leads to high MI properties. The superior soft magnetic and MI properties of these materials arise due to amorphous structure. Of the several soft magnetic alloys, Co-Fe-Si-B based amorphous alloys are found to exhibit large soft magnetic and MI properties. Studies carried out on Co-Fe-Si-B alloys indicate that boron (B) acts as a glass former and a few studies have been carried out to assess the glass forming ability (GFA) of these alloys.3–9 Recently, Arvindha Babu et al.9 have reported the effect of wheel speed on amorphous phase formation, soft magnetic and MI properties of
Co69Fe7Si14B10 alloys. Higher wheel speed (higher cooling rate) led to the formation of amorphous phase with better soft magnetic and MI properties whereas lower wheel speeds (lower cooling rate) yielded orthorhombic Co2Si phase deteriorating the soft magnetic and MI properties. Similar to B, Zr can also be added with Co-based alloys as a glass former as it exhibits all requirements as a glass former.10 It is seen, from Miedema’s model for enthalpy of formation, that Co-B has an enthalpy of mixing DHmix 5 9 kJ/mol atoms, while for Co-Zr it is found to be 41 kJ/mol atoms.11 Since enthalpy of formation of Co-Zr is more negative, Zr addition
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