Local Structure And Properties Of Fe-(Si,B,P,C) Amorphous Alloys

Recently,Fe-based amorphous alloys with superior soft magnetic properties of high saturation magnetization,low coercivity and low loss have a booming development.Alloying and annealing are often used to improve the soft magnetic properties of Fe-based amorphous alloys.Clarifying clearly the mechanism on the structural origin of the alloying and annealing induced enhancement of the soft magnetic properties can guide us to design the composition and annealing process of the amorphous effectively.The relationship between short-range order and magnetic properties of Fe₇₈P₁₄C₈,Fe₈₀P₁₁C₉,Fe₈₀P₁₂C₈,Fe₈₀P₁₃C₇ and Fe₈₂P₁₂C₆ amorphous ribbons were investigated with synchrotron radiation X-ray diffraction and reverse Monte Carlo simulation.Results of pair distribution functions and Voronoi tessellation suggest that the amorphous cluster becomes compacted with the increase of Fe content.Moreover,with P replacing C gradually,more and more P atoms take up the substitutional positions neighboring iron atoms.Meanwhile,the ratio of Fe-centered clusters with coordination number no less than 12 increases.All of these lead to the enhancement of the saturation flux density of Fe-P-C amorphous ribbons.Then,the Fe₈₀P₁₁C₉ amorphous with the best glass formation ability was annealed at low temperature.Variations in the local structure and magnetic properties of Fe₈₀P₁₁C₉ amorphous alloys during structure relaxation have been investigated by XRD,DSC,DC-BH tracer and M?ssbauer spectra.With the increase of structural relaxation time,the saturation magnetization of the ribbon increases gradually but the coercivity firstly declines drastically to a minimum value and then increases slightly,and meanwhile the relative intensity ratio of the 2ⁿdd to the 3^rdd lines of M?ssbauer spectra increases to a maximum value and then reduces.Besides,after structural relaxation,the average hyperfine field of melt spun ribbons increases.The structural relaxation reduces the distance between Fe atoms and the magnetic interaction increases.Meanwhile,it also contributes to the rotation of the easy axis of amorphous alloys towards the ribbon plane,which results in the reduction of coercivity.All of these contribute to the magnetic softening of melt spun ribbons during structural relaxation.Finally,we have investigated variations in the local structure and thermal stability of Fe₈₀Si_8.75B₁₀Cu_1.25.25 amorphous ribbons after thermal cycling treatment between room temperature and77 K.All samples were characterized by X-ray diffraction,transmission electron microscopy,differential scanning calorimetry,magnetometry and transmission M?ssbauer spectroscopy.It confirms that the structure of melt spun ribbons is much compacted after thermal cycling treatment.In addition,the nucleation and growth activation energies ofα-Fe significantly increase after thermal cycling.Moreover,an increase of the saturation flux density from 1.46 T to 1.55 T and a decrease of coercivity from 9.21 A/m to 8.54 A/m can be achieved by the thermal cycling treatment.