Semi-metallic Heusler Materials First Principles Study

Using the projected augmented wave(PAW)method within the generalized gradient approximation(GGA)and GGA+U(on-site Coulomb interaction) respectively by density-functional theory(DFT),we study the equilibrium structural, electronic and magnetic properties of the full-Heusler alloys Co₂ YZ(Y=Y,Ru,Sm,Eu,Sc;Z=Si,Al,Ge,Ga).Within the the generalized gradient approximation,the full-Heusler alloy Co₂YSi and Co₂ScSi show the half-metallic ferrimagnet(HMF)behavior at the equilibrium lattice constants.We show that small compression and expansion of the calculated theoretical equilibrium lattice constants restores the half-metallic ferrimagnetism for the full-Heusler alloy Co₂YSi.Co₂ScSi and Co₂YSi have the similar theoretical mechanism of the half-metallicity.Although the compound of Co₂YGe is not a half-metallic ferrimagnet at the equilibrium lattice constants,it also has a high rate of spin-polarized at the equilibrium lattice constants(94 per cent). While in the GGA+U,although Co₂YSi,Co₂YGe and Co₂ScSi are not half-metallicity at the equilibrium lattice constants,they will have the half-metallic nature in the range of 2 to 6 percents of the compression of the lattice constant.In addition,the magnetic properties of these compounds are studied and the calculated spin magnetic moment of the alloy are gained.We find the Slater-Pauling principle is the necessary conditions of having the half-metallic nature for the Heusler alloys.Moreover by the Calculated spin magnetic moments of the individual atoms in the alloy,it can be found that the magnetic moment of the Co atom depends strongly on the local condition extraordinarily:The change of the atom on the Y position and Z position affected a large extent whether the Heusler alloy is half-metallicity.The atom on the Y position accounts for a leading role.