Studies On The Mossbauer Spectra Of Fe-based Soft Magnetic Alloys

Currently, Fe-based soft magnetic alloys are one of hot information functional materials. Their excellent electromagnetic properties have attracted a wide attention. In this thesis, we choose two kinds of Fe-based soft magnetic alloys(Fe-Si-Al and Fe-Cu-Nb-Si-B) as the study objects and discuss their electromagnetic properties of alloy particles experienced different attrition treatments and heat treatments. Especially, we have employed the M?ssbauer technique, which has an extremely high energy resolution, enable us to know the subtle change in the atomic surrounding around the Fe nucleus due to the solid phase transitions via heat treatments and ball milling processes. Knowing this information will help us uncover the variations in static magnetic properties from the perspectives of the atomic surroundings, and therefore enable us to understand the improved electromagnetic properties on the basis of fundamental physics.This thesis will report the following results and come to several conclusions:Firstly by finely controlling the milling time for Fe-Si-Al particles, the effects of particle shapes on the microwave permeability have been studied. We chose two categories particles for this purpose: as-prepared particles with irregular shapes, the flaky particles obtained by a 30-hours-milling process. The morphologies, static and dynamic magnetic properties have been compared. The results show that the thicknesses of the flaky particles decrease with increasing the milling time, the saturation magnetization is reduced, and the high-frequency complex permeability and permittivity values are increased. XRD measurements show the solid phase transitions occurred during the milling processes. By M?ssbauer studies, it clearly shows the phase transition of Fe-Si-Al from the ordered solid solution(D03 type Fe-Si-Al superlattice) into the disordered solid solution(α-Fe(Si, Al)).Secondly, the proper annealing treatments on Fe-Cu-Nb-Si-B(FINEMENT) ribbons can result in partial nanocrystallization phases in ribbons. It was found that special nanocomposite nanostructures can be obtained in flaky particles to reduce the hi-f eddy current loss: the amorphous ferromagnetic phase with high resistivity is surrounded the ferromagnetic nanocrystalline phases with low resistivity.Finally, for these nanocomposite flakes, their M?ssbauer spectra have been studied with a combined model of the hyperfine interactions: the discrete parameters of hyperfine interactions and the distribution of parameters of hyperfine interactions for the nano phase and the amorphous phase, respectively. According to the fittings on the M?ssbauer spectra, we can learn the degree of nanocrystallization of the amorphous matrix. The high-frequency electromagnetic properties of annealed flakes have been measured. The results indicate that the FINEMET alloy flakes can be an excellent electromagnetic wave absorbent within 1.93-3.2 GHz.