Magnetic properties of multilayers with strong interlayer coupling and perpendicular magnetic anisotropy

研究了具有层间磁耦合和磁各向异性的多层材料的磁性能。这两个特性是现代自旋电子学中磁性器件应用的基本性质，因此得到了广泛的研究。选择Co/Rh和Co/Ir作为研究对象，是因为这两种多层材料同时具有较强的层间磁耦合和磁各向异性。Rh和Ir具有相似的化学性质，因为它们在元素周期表中处于相同的位置，即具有相似的最外层d电子环境和几乎相同的fcc结构晶格参数。此外，Co和这些元素之间的晶格失配约为7%，相对较大，但我们仍然可以期望Co和Rh， Ir之间的外延生长。所有元素都可以在fcc结构中生长，并且能够实现各种生长方向，例如（001）和（111）。样品采用MBE沉积系统制备。为了研究厚度对磁性能的依赖性，沉积了Co或Rh， Ir的楔形层。用SQUID磁强计测量磁化过程。对于Co/Rh（111）多层膜，在Co层厚度小于12的情况下，存在垂直磁各向异性Å。这种各向异性可能源于由于晶格不匹配或表面对称性较低而引起的局部应力。通过对条纹图的分析，导出了面内晶格参数，并估计了面内应力。通过面内应力产生的磁弹性能很好地再现了各向异性。施加垂直于薄膜的外磁场，（001）多层膜的磁化过程显示出比退磁场预期值更高的致敬磁场。在这种情况下，发现了强烈的“负”垂直各向异性，并且可以用与（111）情况相同的方式来解释。

We have investigated magnetic properties of multilayers which have both interlayer magnetic coupling and magnetic anisotropy. These two characteristics have been widely studied because they are essential properties for application to modern magnetic devices in spin-electronics fields. Co/Rh and Co/Ir were selected for the research targets since these multilayers simultaneously posses strong interlayer magnetic coupling and magnetic anisotropy. Rh and Ir have similar chemical properties because they stands at the same raw in the periodic table, namely have similar environments with outermost d electrons and almost the same lattice parameters with fcc structures. Additionally, the lattice mismatch between Co and these elements are about 7 %, relatively large, however we can still expect epitaxial growth between Co and Rh, Ir. All of the elements can be grown in the fcc structure and various growth directions are able to realized, for example (001) and (111).The samples were made by using an MBE deposition system. To study the thickness dependence on magnetic properties, wedged layers of Co or Rh, Ir were deposited. Magnetization process was measured with a SQUID magnetometer. For Co/Rh(111) multilayres, perpendicular magnetic anisotropy was found in the films with Co layer thickness less than 12 Å. This anisotropy can be originated in local stress due to the lattice miss-match or lower symmetry at the surface. From the analysis of streak patterns in RHEED, we derived in-plane lattice parameters and estimated in-plane stress. We found the anisotropy was well reproduced by the magneto-elastic energy generated with in-plane stress. The magnetization process of (001) multilayers applying an external magnetic field perpendicular to the films shows higher salutation magnetic fields than the value expected from the demagnetization field. For this case, strong "negative" perpendicular anisotropy was found and also explainable with the same manner as the (111) case.