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

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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.