Physical Review B (Condensed Matter and Materials Physics) -- November
1, 1999 -- Volume 60, Issue 18 pp. 12957-12962 

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Aperiodical oscillation of interlayer coupling in epitaxial Co/Ir(001)
superlattices

    H. Yanagihara and Eiji Kita 
    Institute of Applied Physics and Center for Tsukuba Advanced Research Alliance (TARA), University of
    Tsukuba, Tsukuba, 305-8573 Japan 

    M. B. Salamon 
    Department of Physics, University of Illinois, Urbana, Illinois 61801 

(Received 12 May 1999) 

High quality epitaxial cobalt-iridium superlattices were successfully grown on MgO(001)
substrates via molecular-beam epitaxy and were found to exhibit anomalous oscillatory
interlayer exchange coupling with a strong coupling constant. The aperiodical antiferromagnetic
(AF) peaks appear at Ir layer thicknesses of 5 Å, 15 Å, and 33 Å. Maximum magnetoresistance
(MR) ratios of 1.1% are obtained and are almost the same for the first and the second AF
peaks. The interlayer coupling corresponding to the first AF peak is so strong that the
magnetization did not saturate even in an applied field up to 90 kOe. The estimated value of the
interlayer exchange constant by MR curves at room temperature is more than 2.2 erg/cm2 close
to the first AF peak. A distinction of the in-plane magnetization process between [100] and
[110] directions is observed and the easy axis of magnetization is found to be along the [110]
axis in plane. The aperiodic oscillations are thought to indicate multiperiodicity of the interlayer
exchange constants. ©1999 The American Physical Society