Magnetic, magnetoelastic and dynamical properties of martensitic Heusler alloys - Ab initio and semi-empiric simulations of structural changes of magnetic shape memory systems by external magnetic fields

用第一性原理计算方法研究了一组Heusler化合物X2YZ(X=Fe，Co，Ni，Cu；Y=Mn，Fe Co；Z=Al，Ga，Ge，In，Sn)高对称立方结构不稳定性的化学趋势。价-电子-原子比e/a的作用已显示出原子间作用力常数的系统性趋势，该常数被发现是结构(马氏体)不稳定性的指标。在本项目中，我们将通过计算结构、电子、磁性和电子-声子性质来继续从头计算，主要集中在新的磁性形状记忆系统Ni-Mn-In、Ni-Mn-Sn、Ni-Mn-Sb和Ni-Mn-(Ga-In)上。最近对Ni2MnIn的一项研究表明，在采用固定自旋矩方法的从头计算中，在原子水平上可以很好地考虑外加磁场对微结构的影响。

First-principles calcutations have been used to investigate chemical trends in the structural instability of the high-symmetry cubic structure for a selected set of Heusler compounds X2YZ (X = Fe, Co, Ni, Cu; Y = Mn, Fe Co; Z = Al, Ga, Ge, In, Sn). Preliminary investigations of the role of the valence-electron-to-atom ratio e/a have shown systematic trends in the interatomic force constant, which is found to be an indicator of the structural (martensitic) instability.In this project, we will continue these ab initio investigations by calculating the structural, electronic, magnetic and electron-phonon properties, mainly concentrating on the new magnetic shape memory systems Ni-Mn-In, Ni-Mn-Sn, Ni-Mn-Sb and Ni-Mn-(Ga-In). A recent study of Ni2MnIn has shown that the effect of an external magnetic field on the microstructure at an atomic level can well be taken care of in the ab initio calculations by using the fixed-spin moment method.