系列CoMnZnZ四元Heusler化合物的结构和半金属铁磁性

Structure and half-metallic ferromagnetism of quaternary Heusler compounds CoMnZnZ

通过第一原理计算理论预测了CoMnZnZ(Z=Si,Ge,Sn,Pb)系列Heusler合金的弹性常数、电子结构和磁性,并根据弹性常数计算得到弹性模量等参量,计算了该系列化合物声速和德拜温度.计算采用全势线性缀加平面波方法,交换相关函数采用基于Perdew-Burke-Ernzerhof的广义梯度近似泛函.弹性模量结果表明晶体呈现韧性特征;承受剪切的性能弱于承受单轴压缩的性能;结构组成具有较低的各向异性性能.电子结构的计算显示CoMnZnZ(Z=Si,Ge,Sn)三个化合物属于半金属铁磁体,但是CoMnZnPb化合物并不显示半金属特性.CoMnZnZ(Z=Si,Ge,Sn)三个化合物的磁矩通过Slater-Pauling法则进行计算得到的量值与第一原理计算得到的完全一致,遵从总的价电子数减去28的Slater-Pauling法则,三个化合物磁矩为整数且自旋极化率为100%.利用轨道杂化理论解释了此系列化合物半金属性的根源.

Using the first principle full-potential linearized augmented wave method we study the electronic structure and elastic and magnetic properties of CoMnZnZ(Z=Si,Ge,Sn,Pb)LiMgPdSn-type Heusler alloys.These compounds have the composition CoMnZnZ with 1︰1︰1︰1 stoichiometry,where Z denotes the main group element Si,or Ge,or Sn,or Pb.The exchange-correlations are treated within the generalized gradient approximation of Perdewe-Burke-Ernzerhof.For each of all studied Heusler alloys,the ferromagnetic state is considered to be more stable than the paramagnetic state,judged by the energy.The total energy of the magnetic calculation is lower than that of the nonmagnetic state for each of all three serise compounds at the equilibrium lattice constant,indicating that the magnetic state is more stable than the nonmagnetic state.We determine the elastic constants C11,C12 and C44,which have not been established previously in experiment nor in theory.The elastic constant indicates the weakened resistance to sheardeformation compared with the resistance to unidirectional compression.We derive other mechanical parameters,i.e.,the shear modulus G,Young’s modulus E,Poisson’s ratio n,and shear anisotropic factor A,which are the important elastic moduli for applications.These compounds each have a lower anisotropy and possess a low probability to develop microcrack or structural defect in its growing process.The sound velocity and Debye temperature for each of the CoMnZnZ(Z=Si,Ge,Sn,Pb)compounds in their stable structure are calculated.The CoMnZnPb exhibits the lowest Debye temperature,and the highest value is observed for CoMnZnGe.The electronic structure calculations show that CoMnZnZ(Z=Si,Ge,Sn)each exhibit a gap in the band of minority states,and they are clearly half-metallic ferromagnets,except for the CoMnZnPb.The CoMnZnZ(Z=Si,Ge,Sn)compounds and their magnetic moments are in reasonable agreement with the Slater-Pauling rule,and they comply with a Slater-Pauling rule of Mt=Zt– 28,which indicates the half metallicity and high spin polarization for these compounds.The CoMnZnSi compound has the largest half-metallic gap value and the gap is about 0.66 eV.The magnetic properties are primarily determined by the Mn atoms,which contribute the highest magnetic moments.The localmoment of the Z element atom is negligibly small.The hybridization of the d orbitals between Co and Mn can explain the origin of the Slater-Pauling rule in half-metallic quaternary Heusler alloys.The half-metallic gap comes mainly from the interaction between the Co and Mn atoms.