First-Principles Study On The Half-metallicity Of Quaternary Heusler Alloys

The electron has spin and charge two properties.The traditional semiconductor physics put particular emphasis on the charge properties of electron,so its spin properties have not been well developed and applied.As the second revolution of electronics,spintronics combines the charge and spin properties of traditional electrons and expected to develop multifunctional devices with stronger performance,lower power consumption and higher integration,has been becoming an emerging field with great development significance.At present,the search for magnetic materials with high spin polarization is a very important problem in the field of spintronics.The half metallic materials have 100%spin polarization near the Fermi level,and can be used in the preparation of spintronic devices extremely.In this work,the quaternary Heusler alloys composed of transition metals or transition metals and heavy metal elements were studied.First principles calculation based on Density Functional Theory is used to study the structural configuration,electronic structure,magnetic properties and half metallic properties of these materials.The main results are summarized as follows:The theoretical calculation results show that the stable structure of CoCrMnZ(Z=Al,Si,Ga,Ge,Sn,Sb)alloys have highly ordered atomic occupation,namely:Co(0.5,0.5,0.5),Mn(0.25,0.25,0.25),Cr(0,0,0)and Z(0.75,0.75,0.75).All the Heusler alloys studied have negative formation energy and can be synthesized by experiment.The electronic structures calculation results can be predicted theoretically that CoCrMnSi,CoCrMnGe and CoCrMnSb alloys are half metallic materials.By changing the lattice constant,CoCrMnZ(Z=Al,Ga,Sn)can also have half metallic properties,and their half metallic properties can be keep stable under a certain uniform strain.The GGA+U calculation method corrects the on-site correlation between electrons and electrons in the transition metals of a series of Heusler alloys,so that CoCrMnZ(Z=Al,Si,Ge,Sb)alloys all show half metallic behavior.The GGA+U calculation method has higher accuracy.First Principles calculation show that the atomic occupation of steady state FePtMnZ(Z=Al,Si,Ga,Ge,Sn,Sb)alloys is:Fe,Pt,Mn and Z atoms occupy(0,0,0),(1/2,1/2,1/2),(1/4,1/4,1/4)and(3/4,3/4,3/4)positions respectively.The atomic occupation satisfies the principle that the elements with high valence electron number occupy the high position and the elements with low valence electron number occupy the low position.The calculation of monoatomic states show that the formation energy for alloys have a negative value,which is expected to be synthesized in experiment.The electronic structure analyzed of this kind of material and predicted that FePtMnSi alloy is a half metallic ferromagnetic material.And the half metallicity will not disappear within a wider range of lattice constants,indicate that the half metallic properties are relatively stable in FePtMnSi Heusler alloy.At the same time,with the change of lattice parameters,FePtMnZ(Z=Al,Ge,Sn)alloys also show half metallic behavior.The calculated results show that the total magnetic moments of the alloy materials which exhibited half metallic behavior are integer and satisfy the Slater Pauling rule.The calculation by adding U to Fe atom,the results show that FePtMnZ(Z=Al,Si,Ga,Ge)are all half metallic ferromagnetic materials,and the band gap is more than 500meV.