Biquadratic coupling in Fe/Au/Fe trilayers: Experimental evidence for the magnetic-dipole mechanism

We have compared the biquadratic coupling in epitaxially grown Fe/Au/Fe(100)-systems with different interface roughness. The profound short-period oscillations observed on the smooth samples are found to be wiped out for the sample with rougher interfaces. In addition, a stronger biquadratic coupling has been observed. For all measured Au-interlayer thicknesses (1.3–2.4 nm) the biquadratic coupling dominates the antiferromagnetic and ferromagnetic coupling, in contrast to the measurements of the samples with smooth interfaces. The observed increase in biquadratic coupling can be explained in the frame of the currently proposed magnetic-dipole mechanism. The experimental results are in a good agreement with the calculation based on this mechanism, which used the roughness parameters obtained by scanning tunneling microscopy and which did not need any fitting parameters. Thus the existence of the magnetic-dipole coupling mechanism has been confirmed experimentally.