Oscillatory biquadratic coupling in Fe/Cr/Fe(001)

Polar Kerr measurements have been used to measure the dependence of the biquadratic coupling strength B-12 on Cr thickness in an Fe/Cr/Fe trilayer. The overall behavior, which consists of a maximum coupling strength at d(Cr)=5 Angstrom (3.5 ML) with a falloff at greater Cr thicknesses, is found to be consistent with in-plane Kerr and Brillouin light-scattering measurements performed on the same sample. The polar Kerr measurements suggest additionally that B-12 increases from zero near zero Cr thickness, and that it oscillates in magnitude after the first peak, with a second peak in B-12 occurring at about d(Cr)=12 Angstrom (8.3 ML). The positions and heights of the first and second biquadratic coupling maxima, in relation to the first bilinear coupling maximum, show excellent agreement with previous measurements by Kobler et al. of the biquadratic coupling behavior in Fe/Cr/Fe, and also show good agreement with the predictions of an intrinsic biquadratic coupling mechanism due to Edwards et al.