Magnetic properties and atom-scale interface structure of epitaxially grown metallic strained superlattice

由于超晶格界面处的结构影响磁性，因此研究其结构细节是非常重要的。在晶体生长过程中，晶格的连续性是人们关注的焦点之一。反射高能电子衍射（RHEED）使我们能够研究晶体生长过程中的表面结构。安装在我们的分子束外延（MBE）系统中的RHEED系统使我们能够实时连续观察表面面内晶格常数的变化。因此，我们研究了[Co/NM]（NM=Au，Ag）二元超晶格和[M1/Co/M2]（M1，M2=Au，Cu）三元超晶格的晶体生长。我们还研究了[M1/Co/M2]三元超晶格的磁性。讨论了垂直磁各向异性与界面结构的关系。在Co/Au超晶格中，Co在Au上的面内晶格常数是连续变化的，而在Co/Ag超晶格中，面内晶格常数是不连续的。因此，在Co/Au超晶格中，Co层中引入了较大的晶格应变，而在Co/Ag超晶格中，应变很小。在由同种原子种类和相反沉积顺序组成的Cu/Co/Au和Au/Co/Cu超晶格中，晶格常数连续变化，但变化量不同。Co在Cu/Co/Au超晶格中比在Au/Co/Cu超晶格中具有更大的弹性应变。弹性应变较大的Cu/Co/Au超晶格表现出较大的垂直磁各向异性。

Since the structure at/near the interface of superlattices influences magnetic property, it is important to investigate details of the structure. In the crystal growth, continuity of the crystal lattice is one of the interesting points. The reflection high energy electron diffraction (RHEED) allows us to investigate the surface structure during the crystal growth. The RHEED system installed in our molecular beam epitaxy (MBE) system enables us to observe, continuously, the change of the surface in-plane lattice constant on a real-time basis. Thus we have investigated the crystal growth of [Co/NM] (NM=Au, Ag) binary superlattices and [M1/Co/M2] (M1, M2=Au, Cu) ternary superlattices. We have also investigated magnetic properties of [M1/Co/M2] ternary superlattices. Moreover, we discuss the relation between the perpendicular magnetic anisotropy and the interface structure. Here, the description [M1/Co/M2] means that the deposition sequence is of Co on M2 and M1 on Co/M2.In the Co/Au superlattice, the in-plane lattice constant changes continuously Co on Au, while in the Co/Ag superlattice, that is discontinuous. Therefore, in the Co/Au superlattice the large lattice strain is introduced to the Co layrs, while in the Co/Ag superlattice little strain is contained. In the Cu/Co/Au and Au/Co/Cu superlattices consisting of the same kind of atomic species and the reverse deposition sequences, the lattice constants change continuously, but the amount of the change are different. Co in the Cu/Co/Au superlattice contains more elastic strain than that in the Au/Co/Cu superlattice. The Cu/Co/Au superlattice containing more elastic strain shows larger perpendicular mangetic anisotropy.