Magnetic and Optical Excitations in Spin-Denstiy-Wave Chromium

本研究的目的是了解自旋密度波铬的磁和光激发，如中子衍射测量中观察到的自旋波以外的未解析磁激发和光吸收光谱中的磁圆二色性，以及实际电子结构。然而，层状结构的铬超晶格实验的大量增长阻碍了研究朝着最初的目标前进。本研究已转向铬超晶格，特别是铁/铬超晶格中自旋密度波的第一性原理研究，重点研究了层间磁耦合与自旋密度波的关系。利用KKR方法，在LSD理论框架内，对Fe/Cr超晶格（一个相当大规模的超晶格）的第一性原理电子结构进行了令人满意的计算。计算取得了较好的结果；例如，计算解释了层间磁耦合的振荡与双单层周期和振荡的相滑移，这对应于Cr层中的磁序从反铁磁到自旋密度波的转变。计算结果表明，Fe/Cr超晶格中的自旋密度波与体态Cr中的自旋密度波不同，这一结果不仅对理解自旋密度波态的电子结构，而且对理解金属超晶格的电子结构都具有重要意义。在这方面，对其他铬超晶格如V/Cr超晶格的进一步研究是有前景的，研究仍在进行中。

The Present research was aiming to understand magnetic and optical excitations in spin-density-wave chromium, such as, unresolved magnetic excitations observed in neutron diffraction measurements other than a spin-wave one and magnetic circular dichroism in photoabsorption spectra, in the light of a realistic electronic structure. Consider-able growth of experiments for chromium superlattices with layered structures, however, has prevented the research from advancing toward the original aim. The research has turned its aim to a first-principles study of spin-density wave in chromium superlattices, in particular, Fe/Cr superlattices, where much attention is paid to the relation between interlayer magnetic coupling and spin-density wave. The first-principles electronic structure calculation for Fe/Cr superlattices, which is a fairly large-scale one, is satisfactorily performed by means of the KKR method within the framework of the LSD formalism. The calculation attains fruitful results ; for example, the calculation explains an oscillation of the interlayer magnetic coupling with a two-monolayer period and also a phase slip of the oscillation, which corresponds to a transition of the magnetic order in the Cr layer from an antiferromagnetic one to a spin-density-wave one. The calculation reveals that the spin-density-wave in Fe/Cr superlattices differs from that in bulk Cr, which result is significant for understanding of the electronic structure of not only a spin-density-wave state but also metallic superlattices. In this respects, a further study of other chromium superlattices like V/Cr superlattices is promising, and the research is still in progress.