Theoretical Studies On Electronic And Magnetic Regulation Of Iron-based Alloys

Materials with different configurations of lateral magnetic properties are often used in ultra-high-density magnetic recording applications and spintronic devices.Iron-based alloys have abundant reserves,good mechanical properties,strong oxidation resistance,and rich adjustable magnetic properties.They are candidate materials for this kind of magnetic materials.The research topic of this thesis focus on the magnetic regulation of iron rich Fe₁₀X₆(X=Si?Al)alloy by using structure disordering and defect/strain enginering.The structural characteristics,magnetic and electronic structures of B₂ phase and chemically disordered A₂ phase are compared by using the method of first principle calculation.The theoretical results provide a theoretical foundation for the design of iron-based alloy magnetic materials with stable structure,rich magnetic regulation and low price.Firstly,the structure,magnetic properties and electronic structure of B₂ phase and chemically disordered A₂ phase of Fe₁₀X₆(X=Si and Al)alloy were studied.B₂ phase has stable Cs Cl structure.The magnetic moment of B₂-Fe₁₀Si₆ cell is?8?_B,but the magnetic moment of B₂-Fe₁₀Al₆ alloy is only?4?_B.According to the degree of spin polarization of Fe atoms,B₂ structure can be divided into Fe_?atom with high magnetic moment and Fe_?atom with low magnetic moment.The volume of the chemically disordered A₂ phase that has a metastable bcc structure expands and the magnetic moment increases compared with the B₂ structure.Especially for A₂-Fe₁₀Al₆ alloy,although the magnetic moment of the system varies with the coordination environment around the Fe atom,the existence of antiposition defect in the system increases the magnetic moment by?375%.The analysis of its electronic structure shows the enchancement of electron exchange splitting in A₂ structure and the disappearance of Fe_?atom in A₂ structure resulting in the increase of the total magnetic moment of the system.The atom radius and electron of the Al atom has a good matching with the Fe atom,so the improvement of the magnetism of iron-based alloy is more obvious.The effects of vacancy and strain on the magnetic and electronic properties of the system were then studied by introducing vacancy defects and strain.The calculation of defect formation energy shows that the Fe vacancy in pure iron layer is easier to form.Through electron spin density analysis,it is found that the magnetic moment of Fe atoms near the Fe vacancy in iron layer increases.As a comparsion the magnetization direction of Fe atoms far away from the Fe vacancy in iron layer reverses,forming antiferromagnetic coupling in the system,which has little effect on the improvement of the overall spin performance of the system.Comparing the changes of magnetic moment of A₂ configuration and B₂ configuration,it is found that the magnetic moment of A₂configuration increases slowly with strain,while the magnetic moment of B₂configuration changes significantly in"V"shape with strain,and the magnetic moment of the system increases sharply at 2%strain.Correspondingly,the increase of d _Fe-Al in B₂configuration is more obvious,the increase of magnetic moment of Fe _I atom in B₂configuration is less than that of Fe _II atom,because there are more occupied states at fermi level of Fe _II atom and the electrons are more active with the strains.The theoretical calculation results of this subject provide good theoretical support for the experimental design of iron-based alloys with different in-plane magnetic structures.