Study of the dynamic of crystallization of an amorphous Fe40Ni40P14B6 ribbon through Johnson-Mehl-Avrami model

Abstract

The study of the crystallization process of an amorphous Fe40Ni40P14B6 ribbon which is grown by the melt-spinning is reported. Differential scanning calorimetry (DSC), thermogravimetry (TGA), X-ray diffraction and magnetization measurements are used to investigate its dynamic of crystallization. DSC measurements show that a well-pronounced exothermic peak corresponding to first crystallization changes as function of the heating rate. For using the temperature calibration procedure of the thermogravimetric equipment, we are able to observe both the transition magnetic temperature of amorphous phase and the crystallization step observed in the differential scanning calorimetry measurements. The analysis of the dynamic of crystallization through Johnson-Mehl-Avrami (JMA) model allows us to state that the nucleation and grain growth processes occur by diffusion controlled growth. The analysis of the X-ray diffraction ex situ carried out after heating confirm the appearing of nanocrystalline Fe3B0.63P0.37 and Ni3P grains (of ≈40 nm) which are likely embedded inside a residual amorphous matrix. Finally, the increasing the crystallized fraction takes an important role on saturation magnetization and magnetic anisotropy.