First-principles Study Of Novel Functional Heusler Structural Materials

The electron has charge and spin properties.The traditional semiconductor physics mainly focused on the electronic properties of charge.However,the electronic properties of spin were ignored.Spintronics,the second life of electronics,has been becoming an important emerging field,expected to overcome the limits of traditional microelectronics.Recently,there is an increasing interest in the spintronic materials,especially the half-metallic(HM)ferromagnets,in which one spin channel is metallic,while the other is semiconducting,and hence 100% spin polarization is expected.The magnetic Heusler compounds have become increasingly attractive in spintronics devices since the half-metallicity and magnetic shape memory effect were discovered in some Heusler alloys.The rich physical properties are being developed in the Heusler alloy family,being a huge treasure house of searching for new functional materials.It has exhibited great potential applications in magnetocaloric,magnetoelectric,and magnetomechanical fields.In this work,several new functional materials with Heusler structure were designed and their basic physical properties were studied.The following is the research results:By continuously substituting Fe for Ti,Al,or Ti-Al,the Fe-based single atomic chains with 100% spin polarization are designed in the CoFeTiAl quaternary semiconductor matrix.We have investigated the electronic structures and magnetic characteristics of the Fe-based supercells by using the first-principles calculations.All the materials are half-metallic and a conductive nanopillar is formed in CoFeTiAl matrix.The width of the nanopillar is about half of the lattice parameter,of which the length will be adjustable.It would be an ideal method to design the new direct-current-magnetic memory device.The electronic structures and magnetic properties of quaternary Heusler alloys KCaCF and KCaCCl have been analyzed by means of first-principles calculations on the basis of density functional theory.We found the most stable configuration where C occupies(0,0,0)site,K(0.25,0.25,0.25),F/Cl(0.5,0.5,0.5),and Ca(0.75,0.75,0.75)and the metastable structure in which K,Ca,C,and F/Cl occupy(0,0,0),(0.25,0.25,0.25),(0.5,0.5,0.5),and(0.75,0.75,0.75)sites,respectively.Both of them arehalf metals with equilibrium volume.The spin polarization is predominantly from C2 p states.With the variation of the lattice constant,spin-gapless semiconducting characteristic is achieved for metastable KCaCCl as volume increases.With the first-principles calculations,the electronic structure and magnetic properties of KCaCX(X=O,S and Se)alloys with quaternary-Heusler structure have been studied.The results show that KCaCO is a new bipolar ferrimagnetic semiconductor,while KCaCS and KCaCSe are fully compensated ferrimagnetic semiconductors.The strong spin polarization mainly derives from the 2p electrons of C element in the KCaCX(X=O,S and Se)compounds.Under the effect of hydrostatic strain and tetragonal distortion,all the alloys undergo an interesting physics change.Therefore,KCaCX(X=O,S and Se)compounds would be a series of potential candidates for new spintronics device.