Electronic?Magnetic And Transport Properties Of Quaternary Heusler Alloys

Since the discovery of the first half-metallic material NiMnSb in 1983,the semi-metallic Heusler alloy has received increasing attention.The electronic structure of this material near the Fermi level has a unique property,that is,the spin-up appears as a metal characteristic,and the spin-down appears as a semiconductor characteristic,thereby having a complete(100%)spin polarization.For spintronic devices,efficient spin injection requires full spin polarization of the carrier,while high the Curie temperature is a prerequisite for room temperature applications,many of which are very useful for technical applications.In this paper,the properties of quaternary Heusler alloy compounds were studied by first-principles calculation and experimental synthesis.The important results are as follows:1.Electronic structureThe electronic structure of CoFeMnSn was studied by first-principles calculation based on density functional theory.The atomic occupancy is Fe(0,0,0),Mn(0.25,0.25,0.25),Co(0.5,0.5,0.5)and Sn(0.75,0.75,0.75)have the lowest configuration energy.The results of energy band and density of states indicate that the spin-up CoFeMnSn has no band gap,while the spin-down species have a forbidden band of 0.31 eV and a total magnetic moment of 4.07 ?B,suggesting that CoFeMnSn is a spin gapless semiconductor.The electronic structures of CoTiMnSn,CoVMnSn and CoCrMnSn were calculated by substituting Ti,V and Cr for Fe,respectively.the result shows:There is no band gap when the energy of CoTiMnSn is the lowest,and the total magnetic moment is 0.CoVMnSn is a half-meta,which have the band gap of 0.14 eV downward and the total magnetic moment of 1 ?B when the energy is the lowest.CoCrMnSn is also a half-metal,which have a band gap of 0.34 eV downward and the total magnetic moment of 7.72?B when the energy is the lowest.2.Crystal structureThe quaternary alloy CoFeMnSn was synthesized by arc melting method.X-ray diffraction pattern analysis showed that CoFeMnSn is a novel Heusler alloy with ordered B2 crystal structure.3.Magnetic propertiesThe measurement results of the M-T curve indicate that:The Curie temperature of CoFeMnSn is about 579 K,and the saturation magnetization magnetic moment is 4.08?B,which is basically consistent with the theoretically calculated total magnetic moment of 4.07 ?B,following the Slater-Pauling rule.4.Transport propertiesThe change in resistivity of CoFeMnSn with temperature indicates:The CoFeMnSn alloy exhibits semiconductor characteristics over the experimentally measured temperature range(400?4.2 K).The Hall coefficient R0 of CoFeMnSn is positive,indicating that it is a p-type semiconductor.The anomalous Hall effect of oFeMnSn alloy is mainly due to the contribution of skew scattering and intrinsic mechanism.