Department of Physics, University of Washington, Seattle, WA 98195, USA.
J Phys Condens Matter. 2010 Apr 14;22(14):146002. doi: 10.1088/0953-8984/22/14/146002. Epub 2010 Mar 17.
The length scale of the local chemical anisotropy responsible for the growth-temperature-induced perpendicular magnetic anisotropy of face-centered cubic CoPt(3) alloy films was investigated using polarized extended x-ray absorption fine structure (EXAFS). These x-ray measurements were performed on a series of four (111) CoPt(3) films epitaxially grown on (0001) sapphire substrates. The EXAFS data show a preference for Co-Co pairs parallel to the film plane when the film exhibits magnetic anisotropy, and random chemical order otherwise. Furthermore, atomic pair correlation anisotropy was evidenced only in the EXAFS signal from the next neighbors to the absorbing Co atoms and from multiple scattering paths focused through the next neighbors. This suggests that the Co clusters are no more than a few atoms in extent in the plane and one monolayer in extent out of the plane. Our EXAFS results confirm the correlation between perpendicular magnetic anisotropy and two-dimensional Co segregation in CoPt(3) alloy films, and establish a length scale on the order of 10 Å for the Co clusters.
使用偏振扩展 X 射线吸收精细结构（EXAFS）研究了导致面心立方 CoPt(3) 合金薄膜生长温度诱导垂直各向异性的局部化学各向异性的长度尺度。这些 X 射线测量是在一系列外延生长在（0001）蓝宝石衬底上的四个（111）CoPt(3) 薄膜上进行的。当薄膜表现出磁各向异性时，EXAFS 数据显示出与薄膜平面平行的 Co-Co 对的偏好，而在其他情况下则显示出随机的化学有序性。此外，原子对关联各向异性仅在吸收 Co 原子的近邻和通过近邻聚焦的多次散射路径的 EXAFS 信号中得到证明。这表明 Co 团簇在平面内的范围不超过几个原子，在平面外的范围不超过单层。我们的 EXAFS 结果证实了 CoPt(3) 合金薄膜中垂直各向异性与二维 Co 偏析之间的相关性，并确定了 Co 团簇的长度尺度约为 10 Å。
