Morphology And indirect exchange coupling in Fe/Cr/Fe(110) trilayers

We investigated the indirect exchange coupling in W(110)/Fe/Cr/Fe/Cr films. Magnetic interface anisotropies of the W/Fe and Fe/Cr interface differ in sign and thus allow the preparation of Fe films with orthogonal adjustable uniaxial anisotropies. The bilinear (J(1)) and biquadratic (J(2)) exchange coupling constants were determined from magnetization curves independent of magnitude and sign. We determined J(1) and J(2) as a function of Cr interlayer thickness (t(Cr)=0-4 nm) and temperature (T=100-300 K). Moreover, we varied the morphology of the interlayer as determined by high-resolution low-energy electron diffraction using different substrate temperatures (T-p,T-Cr=100-500 K) during evaporation of the Cr spacer. Results for the exchange coupling versus spacer thickness are related to the particular lateral thickness fluctuation of the spacer. Our results are in good agreement with the bilinear coupling predicted by ab initio theories. Extrinsic biquadratic coupling models explain J(2) observed experimentally.