The Reseach Of Magnetic Properties,half-metallicity And Thermoelectric Properties Of Heusler Alloy Co_2-xFe_xVAl

Due to the special electronic structure,Heusler alloy has great development value and application potential.On the one hand,because of the unique half-metal structure,it can be well applied to spintronic devices.Co₂VAl has good half-metallic property and high spin polarization,while Fe₂VA1 has no magnetic moment.Combining the properties of the two alloys,new materials with high spin polarization and lower magnetic moment can be found.On the other hand,the alloy has a narrow gap at the Fermi level,which makes the alloy have a larger Seebeck coefficient,providing the possibility to optimize the thermoelectric properties of the material,and the Fe₂VAl alloy has semiconductor-like property.In this paper,We study the Heusler alloy Co_2-xFe_xVAl?x=0,0.5,1,1.5,2?.Combination of first-principles calculations and experiments,the crystal structure,saturation magnetic moment,electrical transport properties and thermoelectric properties of the alloys were investigated with the increase of Fe content.The main contents are as follows:1.Using the first-principles calculation,the relationship between the crystal structure,magnetic,semi-metallic properties and relative formation energies of Heusler alloy Co_2-xFe_xVAl in fully ordered and partially disordered state and Fe doping concentration were studied.It is found that the fully ordered magnetic properties decrease with the increase of Fe content,basically satisfy the Slater-Pauling?SP?,and the spin polarization ratio is also high.Fe₂VAl has semiconductor characteristics and its magnetic moment is zero;Partially disordered half-metallic loss and deviated from the SP.2.The Co_2-xFe_xVAl series alloy was prepared by vacuum arc melting method,and the alloy was heat treated under different conditions.The structure,magnetic properties and transport properties of Co_2-xFe_xVAl alloy were discussed and analyzed.It is found that the alloy Co_2-xFe_xVAl is easier to generate the ordered phase under the heat treatment process of annealing at 900°C with 48 h,cooling at ice water.At this time,the change of magnetic and electrical resistance of the alloy is consistent with the calculation of complete order.3.The alloys were prepared by vacuum arc melting and spark plasma sintering approaches and the thermoelectric parameters including Seebeck coefficient,electrical resistivity,thermal conductivity and ZT value were measured.The Fe₂VAl alloy Seebeck coefficient is the largest near the room temperature during the test temperature range.Due to the distortion of crystal lattice,other defects or the uncertainty of polycrystalline fine grains,the ZT value of Fe₂VAl alloy is relatively small.The ZT of Fe_1.5Co_0.5VAl is relatively the largest due to B32a disorder structure or the influence of other factors?to be further studied?.Therefore,by adjusting the content of doping elements and adjusting the process to improve the structure of the alloy,the thermoelectric properties of the alloy is optimized.