Study of the Effect of Grain Structure and Phase Constitution on the Magnetic Properties of Nanocrystalline fe72.5cr1nb3cu1si13.5b9 alloy

Abstract

This thesis is based on the experimental investigation of the effect of grain size and phase constitution on the magnetic properties of nanocrystalline Fe72.5Cr1Nb3Cu1Si13.5B9 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 450oC to 800oC for 30 minutes. DTA runs for the sample show the existence of tow exothermic peaks one for and other for Fe2B phase. Thermal analysis experiment and from the obtained data activation energy of primary crystallization products phase is 3.26eV and secondary crystallization products for Fe2B is 4.87eV. The XRD experiments are in order to study the effect of structural parameters such as lattice parameter, grain size and silicon content of the nanocrystalline grain. In the optimized annealing condition the grain size has been obtained in the range of 10-30nm. The peak shift indicates the change of the values of Si-content of nanograins and therefore, the change of the values of lattice parameter of nanograins. The saturation magnetization (Ms) has been observed 122.6emu/gm and in as prepared condition Curie temperature (Tc) has been found to be 316oC, which quite close compared to the Tc of conventional FINEMET (i,e, sample without Cr). The critical composition for disappearance of ferromagnetism fall of curves Ms with the replacement Fe by Cr, 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.