Study of Nanocrystalline Formation of Magnetic Properties in fe72.5ag2nb3si13.5b9 Metallic Ribbon

Abstract

This thesis focuses on the experimental investigation of the effect of grain size and phase constitution on the magnetic properties of Fe72.5Ag2Nb3Si13.5B9 alloys in the amorphous and annealed states. The sample has been prepared by rapid solidification technique and their amorphous nature has been confirmed by X-ray diffraction (XRD). The crystallization behavior and the nanocrystal formation have been studied by Differential Thermal Analysis (DTA) and XRD. Magnetization measurements have been carried out using vibrating sample magnetometer (VSM). The ribbon sample has been annealed in a controlled way in the temperature range 550oC to 750oC for 2 hours. DTA runs for the sample show the existence of one exothermic peak for α-Fe(Si) phase. Thermal analysis experiment and from the obtained data activation energy of primary crystallization products α-Fe(Si) phase is 5.78 eV. The XRD experiments are in order to study the effect of structural parameters such as lattice parameter, crystallites size and silicon content of the nanocrystalline α-Fe(Si) grain. In the optimized annealing condition the grain size has been obtained in the range of 50 - 69nm. The peak shift indicates the change of the values of Si-content of nanograins and therefore, the change of the lattice parameter of nanograins. The saturation magnetization (Ms) has been observed 114emu/gm and in as prepared condition Curie temperature (Tc) has been found to be 305oC. The critical composition for disappearance of ferromagnetism fall of curves Ms with the replacement Cu by Ag of FINEMET, where the nearest neighbor coupling to longer dominant and intermediate range occurs and the magnetization process of this amorphous ribbon sample are soft behavior of magnetic material.