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

由于超晶格界面处或界面附近的结构会影响磁性能，因此研究结构的细节是很重要的。在晶体生长中，晶格的连续性是研究的热点之一。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。安装在分子束外延（MBE）系统中的RHEED系统使我们能够实时连续地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。此外，我们还讨论了垂直磁各向异性与界面结构的关系。这里的描述[M1/Co/M2]表示沉积顺序是Co在M2上，M1在Co/M2上。在Co/Au超晶格中，面内晶格常数在Au上连续变化，而在Co/Ag超晶格中，这是不连续的。因此，在Co/Au超晶格中，Co层中引入了较大的晶格应变，而Co/Ag超晶格中包含的应变很小。在相同原子种组成的Cu/Co/Au和Au/Co/Cu超晶格中，在相反的沉积顺序下，晶格常数连续变化，但变化的量不同。Cu/Co/Au超晶格中的Co比Au/Co/Cu超晶格中的Co含有更多的弹性应变。含有更多弹性应变的Cu/Co/Au超晶格表现出更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.