The influence of an isothermal annealing process on the structure and magnetic properties of the bulk amorphous alloy FeCoBYMo

Abstract

This paper presents the results of research into a bulk amorphous alloy based on Fe. Samples with the composition Fe61Co10Y8Mo1B20 were prepared in the form of plates using an injection-casting method. The samples were then subjected to an isothermal annealing process (at less than the crystallization temperature) of 700 K for 1 h and 770 K for 3.5 h The structures of the samples were investigated, both in the state after solidification and following the heat treatment, using X-ray diffraction (XRD) and Mössbauer spectroscopy. The results confirmed that the samples, both after solidification and after annealing, were amorphous. Magnetic measurements were carried out using a vibrating-sample magnetometer (VSM) with magnetic fields of up to 2 T. Based on these measurements, the effect of the isothermal annealing process on the magnetic properties was defined, including the saturation magnetization μ0Ms and coercive field Hc. Using the Kronmüller theory, the initial magnetization curves were analysed in the area of approach to ferromagnetic saturation. On the basis of this theory, the quantity and quality of the structural defects were defined; these defects play a critical role in the magnetization process in high magnetic fields. Following this study, the sample annealed at 770 K for 1 h was found to feature a relatively low coercive field and the higher value of magnetization saturation. Linear defects, the so-called quasidislocational dipoles, played the leading role in the process of magnetization of the test samples.