Study On Magnetic And Mechanical Properties Of Heusler Alloy Based On First Principles

Based on the previous research and summary,we propose a new Half-Heusler alloy Fe Cr As,and use the first principles calculation software CASTEP to calculate the spin polarization density functional theory,and determine the lattice constant of Fe Cr As alloy in the Half-Heusler structure.We calculated the effect of each element on the Half-Heusler alloy and the formation of the band gap,calculated the total magnetic moment,and carried out the theoretical verification.The range of lattice distortion to keep semi metallic properties was studied to determine the degree of semi metallic stability.The results show that Fe Cr As alloy can maintain 100% spin polarizability in a large range of lattice distortion.In the calculation process,we studied the effect of Fe atom in the crystal cell based on the energy level splitting theory in the crystal field of the complex,and found that the energy level splitting is related to the d-state distribution of Fe atom.Through calculation,we confirm that the Fe Cr As compound of Half-Heusler phase is a new Half-Heusler alloy.Of course,we also analyzed its mechanical properties.Based on the results of bulk modulus,shear modulus,Young's modulus and Poisson's ratio calculated from the elastic constants,it is shown that the Half-Heusler alloy Fe Cr As is a brittle material.There is no virtual frequency in the phonon spectrum,which indicates that the unit cell of the alloy can exist stably.In addition,the effect of Co doping on the magnetic moment of the original Heusler alloy was also investigated.In order to investigate the antiferromagnetic coupling of Co and Mn atoms in Cu2-x Cox Mn1+y Al1-y,a Heusler alloy,under Mn rich condition,our basic research objects are Cu2 Mn Al with only one kind of magnetic atoms and Co2 Mn Al which remain ferromagnetic in Mn rich conditions.After a large number of calculations,we found that because the d-band center of Co atom is higher than Cu atom,then the anti-bonding state of Mn atom is pushed above Fermi level,thus changing the d-orbital electron arrangement of Mn atom,making the original antiferromagnetic Mn atom become ferromagnetic.Based on this theory,a method of applying stress to the alloy to adjust the lattice size to change the magnetic moment of Mn atom is proposed to achieve the same effect as doping special atoms.In addition,it was also inferred that the ferromagnetism of the parent phase and the ferromagnetism of the martensite phase are closely related to the d-band center caused by the change of lattice size.We have done a series of work on the formation of band gap and the change of magnetic moment,which provides an important reference for other researchers.