Lattice Distorition and Electronic Structure of Ferromagnetic Transition Metals and Alloys

本项目的主要目的是研究过渡金属和合金的电子结构与晶格之间的关系。已经尝试了几种不同的方法：本文采用KKR-CPA方法对过渡金属合金的电子结构进行了研究，研究了过渡金属合金中常见的马氏体相变的微观成因。得到了以下结果：(1)通过计算晶格对外力的响应，表明FePd预计会出现fcc-fct不稳定性。(2)本文的第一性原理计算较好地再现了三维合金磁矩的Slater-Pauling曲线。这些合金的晶格常数是通过最小化总能量来确定的：研究了磁性和化学对其黏合性能的贡献。用紧密结合模型研究了Mn在多自旋密度波（MSDW）状态下的电子结构。讨论了d电子数与MSDW态的关系，并在考虑四方畸变的情况下解释了MnFe合金MSDW态的浓度依赖性。为了从第一性原理讨论这种复杂的系统，还编写了LMTO计算机代码。作为一个典型的反铁磁Mn晶格常数的计算，MSDW态的计算以及四方畸变体系的计算正在进行中。利用自由能的朗道展开讨论了与可能的磁性结构相容的晶格分布，并构造了温度与成分跨平面的相图。考虑到三个独立的自旋密度波和晶格畸变之间的耦合，系统地解释了Mn合金中出现的相图。同时解释了在csl型AuMn中出现的两个四方相。

The main purpose of the present project is to study the relation between the electronic structure and the lattice of transition metals and alloys. Several different approaches have been tried: 1. Electronic structure of transition metal alloy are investigated by use of the KKR-CPA method to study the microscopic origin of the martensitic transformation which often is observed for these alloys. The following results are obtained: (1) By calculating the response of the lattice to the external force, it is shown that an fcc-fct instability is expected for FePd. (2) The present first-principle calculation well reproduces the so-called Slater-Pauling curve of magnetic moment of 3d allyoys. (3) The lattice constants of these alloys are determined by minimizing the total energy: a magnetic and a chemical contributions to the cohesive properties are investigated.2. The electronic structure of Mn in the multiple spindensity-wave (MSDW) state is investigated by the tight-binding model. The relation between the number of d electrons and the MSDW state is discussed and the concentration dependence of the MSDW state of MnFe alloys are explained by taking account of the tetragonal distortion. Also to discuss such complicated systems from the first-principle, LMTO computer code is developed. As a typical example the lattice constant of the antiferromagnetic Mn is performed: the calculation of the MSDW state as well as the tetragonally distorted systems are now in progress.3. The lattice distrotion which is compatible with the possible magnetic structure is discussed by use of the Landau's expansion of free energy and the phase diagram in the plane spanned by temperature and composition is constructed. Phase diagrams which appear for Mn alloys are explained systematically by taking account of the coupling between three independnt spin-density-waves and the lattice distortion. Also explained is the two tetragonal phases appearing in CsCl-type AuMn.