On the structural stability of melt spun ribbons of Fe_95−xZr_xB₄Cu₁ (x = 7 and 9) alloys and correlation with their magnetic properties

Abstract

Melt spun ribbons of Fe_95−xZr_xB₄Cu₁ with x = 7 (Z7B4) and 9 (Z9B4) alloys have been prepared and their structure and magnetic properties have been evaluated using XRD, DSC, TEM, VSM and Mossbauer spectroscopy. The Glass Forming Ability (GFA) of both alloys has been calculated theoretically using thermodynamical parameters and Z9B4 alloy is found to possess higher GFA than that of Z7B4 alloy which is validated by XRD results. On annealing, the amorphous Z7B4 ribbon crystallizes into nanocrystalline α-Fe, whereas amorphous Z9B4 ribbon shows two-stage crystallization process, first partially to bcc solid solution which is then transformed to nanocrystalline α-Fe and Fe₂Zr phases exhibiting bimodal distribution. A detailed phase analysis using Mossbauer spectroscopy through hyperfine field distribution of phases has been carried out to understand the crystallization behavior of Z7B4 and Z9B4 alloy ribbons. In order to understand the phase transformation behavior of Z7B4 and Z9B4 ribbons, molar Gibbs free energies of amorphous, α-Fe and Fe₂Zr phases have been evaluated. It is found that in case of Z7B4, α-Fe is always a stable phase, whereas Fe₂Zr is stable at higher temperature for Z9B4.