First Principle Study On The Effect Of Electronic Structure And Magnetic Performance Of M-type Strontium Ferrite

M-type strontium ferrite(SrF122O19)is one of the most common materials in permanent magnet materials,because it has high curie temperature.large saturation magnetization,excellent chemical stability and low price.Therefore,the strontium ferrite have a very importance position in permanent magnet materials.It is widely used in magnetic recording material.magnetic storage material and can be used as an electronic component of a microwave display.However,the magnetic properties of strontium ferrite are obviously lower than the Nd-Fe-B ferrite.Therefore,how to improve the magnetic properties of M-type strontium ferrite materials has become a main research goal of this thesis.In this thesis,the stable magnetic configuration,magnetic properties and electric structure of strontium ferrite are studied by first-principles calculations.Using the first-principles method based on density functional theory was used to study the unit cell with 64 atoms.The generalized gradient approximation GGA and GGA+U method were used to optimize the unit cell structure of strontium ferrite.Compare with the total magnetic moment of the system to obtain the optimal approximation method.We examined nine possible ferromagnetic and multiple ferromagnetic configurations and relaxed all structures.By comparing the energy of all structures,we obtained the most stable configuration for subsequent doping studies.After calculating the most stable strontium ferrite configuration,the electronic structure of our system was calculated and by comparing the band gap values of the system to determine what properties of strontium ferrite,and determine the contribution of different Fe ions to the total density of states and the bonding between Fe atoms and O atoms.The transition element of Mn atom radius is close to the Fe atom,and the Mn atom not cause large lattice distortion after replacing the Fe atom,and the Fe and Mn atoms 3d orbital electron numbers are different,so the Mn atom replaces Fe atom will have a great influence on the total magnetic moment of the system.The first-principle method is used to calculate the substitution of Mn-doped strontium ferrite SrFemMnxO19(x=0.5,x=1.0),we mainly investigated two low levels of doping to determine which Mn atoms are more likely to replace Fe atoms.After obtaining the stable configuration of the Mn-doped strontium ferrite,the electronic structures of strontium ferrite(x=0.5)and(x=1.0)were studied to determine how Mn atoms affect the system band gap.The state of density of the doped Mn atoms is bonded to the surrounding O atoms by state density analysis.Finally,comparing the lattice parameters.magnetic moment change and volume change of the original cell and Mn atom replaces Fe atoms in strontium ferrite,it is determined whether the Mn atol can be reasonably substituted as a dope atom to replace Fe atom in strontium ferrite,it provides a theoretical basis for laboratory research on strontium ferrite magnetic materials.