Research On Magnetism And Metallic Structure Of Part Heusler Alloys

Recently, with the rapid development of technology and deepened exploration in thefield of materials science, Heusler alloys exhibit rich physical properties and manyapplicable functions. Especially, the half-metallicity and ferromagnetic shape memoryeffect have been found in the electronic, machinery, chemicals, energy and other areas.Heusler alloys have stimulated much research interst. In this dissertantion, the first-principle calculations within density functional theory are used to investigate theelectronic structure of the Heusler alloys containing3d,4d elements.We abstract the main content of this dissertation as following:1. The electronic structure and magnetism of the Mn2RhZ (Z=Al, Ga, In, Si, Ge, Sn,Sb) Heusler have been studied by first-principles calculations. The calculated equilibriumlattice constant increases with increasing atomic number of Z atoms in the same columnof the Periodic Table. All these compounds, except for Mn2RhSb, the moments of Mn (A)and Mn (B) are antiparallel to each other. Rh possesses a small moment and its momentis parallel to the large one of Mn (B). Three half-metallic ferromagnets, namely,Mn2RhAl, Mn2RhGe and Mn2RhSb, are predicted. It is found that the total magneticmoments of the three half-metals can keep as an integral value for a wide range ofequilibrium lattice parameters.2. The electronic structure and magnetic properties of Fe2YB (Y=Ti, V, Cr, Mn)Heusler alloys have been studied theoretically. These alloys are all ferrimagnets expectfor Fe2VB. The latter has24valence electrons and is a paramagnetic semimetal. Fe2CrBis predicted to be half-metals at equilibrium lattice constant. The spin polarization ofFe2MnB is also quite high. The calculated total momets are1.00μBfor Fe2CrB and2.04μBfor Fe2MnB. Under uniform lattice distortion, the half-metallicity of Fe2CrB is morestable than Fe2MnB.3. The site preference, electronic structure and magnetic properties of Co2ZrZ (Z=Al,Ga, In, Si, Ge, Sn, Sb) have been studied by first-principles calculations. According theresults, we mainly studied Co2ZrGe alloy. The Cu2MnAl type is more favorable than theHg2CuTi type structure and the equilibrium lattice parameter is6.06. It is found thatCo2ZrGe alloy has an energy gap in the minority spin direction at the Fermi level (EF)whereas the other spin band is strongly metallic. As a result, Co2ZrGe alloy is predictedto be a half-metal with100%spin polarization of the conduction electrons at the EF. Thecalculated total magnetic moment is2.00μBper unit cell, which is in line with the Slater-Pauling curve of Mt=Zt-24. Such an alloy may be a promising material for futurespintronics devices.4. The electronic structure and magnetic properties of the Heusler alloy Ni2YIn (Ti, V,Cr, Mn, Fe, Co) for austenite and martensite phase have been studied by first-principles calculations. According the results, we mainly studied Ni2CoIn alloy. It is clear that thephase transformation from cubic to tetragonal structure lowers the total energyeffectively, indicating the possibility of a martensitic phase transition at low temperatures.Based on Jahn-Teller effect, tetragonal distortion can reduce the orbital degeneracy anddecrease energy of the system, furtherly, Ni2CoIn alloy may have a stable martensitephase.The calculated results agree well with the research results which have been reported,proving the reliability of the computational method used. These theoretical researchesmay be the guidance for the future studying and potential application.