Structural Mechanisms Of Magnetic Properties Modification In Fe-Si-B(-Cu)amorphous Alloys During Annealing

Annealing Fe-based amorphous ribbons below the crystallization temperature to relieve the internal stress their coercivity decreases.However,atomc-scale mechanisms of magnetic property modification have not yet been well understood.This thesis is aimed at finding the structural origin of magnetic softening during annealing.Fe81Si9B10 and Fe80Si9B10Cu1 amorphous ribbons were annealed at 563 K for various periods of time.It was found that the coercivity of alloy ribbons decreases before a slight increase with increasing annealing time.The intensity ratio R of the second to the third lines in M?ssbauer spectra is enhanced during annealing,which means that annealing induces the rotation of easy axis to the ribbon plane and concomitant reduction in coercivity.The structural evolution of Fe81Si9B10 and Fe80Si9B10Cu1 amorphous alloys annealed at various temperatures below the crystallization temperature was then investigated,where the decrease in coercivity with increasing annealing temperature also originates from the rotation of easy axis to the ribbon plane.Through synchrotron radiation X-ray diffraction,it was found that,from short-range order to medium-range order,a positive and negative sign for volumetric thermal strain alternates upon heating and the amplitude of strain decays.Moreover,extending to outer shells,thermal strain seems less temperature-dependent in terms of the rate of increment.Based on synchrotron radiation X-ray diffraction and Fe K-edge extended X-ray aborption fine structure experiments coupled with reverse Monte Carlo simulation,the Voronoi tessellation method was applied to extract the distribution of Voronoi clusters.With the increase of annealing temperature,the number of Voronoi clusters with low local five-fold symmetry decreases while the number of Voronoi clusters with high local five-fold symmetry increases,which implies the relief of structural frustration and resultant decrease in coercivity.By performing synchrotron radiation X-ray diffraction coupled with simulations,the coordination numbers of Fe and Cu around Fe are found to increases with annealing temperature,which indicates Cu clustering initiates and rapidly develops and Fe atoms aggregate in amorphous matrix before primary crystallization.With the Voronoi tessellation method,one can note that numbers of Fe-centered clusters with coordination number no less than 13 and Cu-centered clusters with coordination number no less than 14 gradually increase with the increase of annealing temperature.The number of Voronoi clusters with high local five-fold symmetry increases during annealing,indicating the release of internal stress and resultant reduction in coercivity.