First-principles Study Of The Structure, Electronics, Magnetism And Elasticity Of Binary Heusler Alloy And Its Doped Compounds

The spintronic devices attracted lots of attention in the past,which put spin characteristics into semiconductor devices.The biggest problem is that the injection rate is relatively low.Therefore,scientists propose that we must find a material that it has 100%spin polarization.Later,the German physicist F.Heusler discovered the Heusler alloy for the first time,but its physical properties didn't been studied,due to the experimental conditions.De Groot et al found that the half-Heusler alloy NiMnSb presents half-metal(HM)ferromagnetism at 1983.The electrons cross the Fermi level in one spin direction,showing a metallic character,while in the other spin,they appear a semiconductor nature.According to the spin polarization formula,the half-Heusler alloy NiMnSb possesses 100%spin polarization.In addition,the alloy NiMnSb was also synthesized experimentally,which can be used in spintronic device.Heusler alloy stands out in the application of spintronic devices,due to its high Curie temperature,large magnetic moment and 100%spin polarization.In this paper,the binary Mn-based Heusler alloys Mn2Z(Z=As,Sb,Bi),the binary Mn-based doped alloys Mn2GexAS1-x(x=0.25,0.50,0.75,1.00)and the binary Heusler alloys ZCl3(Z=Be,Mg,Ca,Sr)are investigated based on density functional theory(DFT)by using the first-principles calculations.The mainly conclusions are as follows:(1)The structural,electronic,magnetic and elastic properties of the Mn2Z(Z=As,Sb,Bi)have been studied.The investigations of the density of states and band structures show all three alloys are HM ferrimagnets.The investigations of the magnetic properties show their total magnetic moment Mt is all-1?B/f.u.,satisfying the Slater-Pauling rule Mt=18-Zt.From elastic constants,we find all three alloys are mechanical stable.While from cohesive energy and formation energy,we find both Mn2AS and Mn2Sb alloys are thermodynamic stable,while the Mn2Bi alloy is thermodynamic meta-stable.Furthermore,their HM ferrimagnets characters are maintained in large strain regions for Mn2As,Mn2Sb and Mn2Bi.Finally,under the uniform pressure strain,all three alloys undergo the FiM-HM,FiM-M,NM-M,FiM-M and NM-M phase transitions.(2)The structural,electronic,magnetic and elastic properties of the binary Mn-based Heusler doped Heusler alloys Mn2GexAs1-x(x=0.25,0.50,0.75,1.00)have been studied.Firstly,the Mn2Ge0.25As0.75,Mn2Ge0.75As0.25 and Mn2Ge alloys present a cubic structure,while the Mn2Ge0.5As0.5 compound has a tetragonal structure.Secondly,from the investigations of electronic and magnetic properties,we find that the four alloys are all HM ferrimagnets and their total magnetic moments Mt satisfy with the Slater-Pauling rule Mt=18-Zt.Thirdly,the results of formation energy and cohesion energy show that they are all thermodynamic stable.Finally,both doped Heusler alloys Mn2Ge0.25As0.75 and Mn2Ge0.5As0.5 are mechanical stable under pressure 0-4GPa,while the Mn2Ge0.75As0.25 and Mn2Ge lose mechanical stable when the pressure exceed 1.3 and 0.5GPa,respectively.(3)The structural,electronic and magnetic properties of the binary Heusler alloys ZCl3(Z=Be,Mg,Ca,Sr)have been studied.The investigations of the electronic and magnetic properties show the four binary Heusler alloys ZCl3(Z=Be,Mg,Ca,Sr)are all HM ferromagnets with an integer magnetic moment Mtof 1 ?B/f.u..Combining their cohesive energies and formation energies,we find that the alloy BeCl3 is thermodynamic meta-stable,while other alloys are thermodynamic stable.