Oscillatory interlayer exchange coupling in Ni81Fe19/Cu/Ni81Fe19/Fe50Mn50 spin valves

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Abstract
An oscillatory behavior is observed in the indirect exchange coupling between the two ferromagnetic layers in sputtered 〈111〉 and 〈100〉 Ni81Fe19/Cu tCu/Ni81Fe19/Fe50Mn50 spin valves. The periods of oscillations are 13.5 and 12.5 Å for the 〈111〉 and 〈100〉 growth directions, respectively. The coupling changes from strongly ferromagnetic, at tCu=12 Å, to antiferromagnetic at tCu=9.5 Å. At the transition region where the bilinear coupling changes sign (tCu≊10 Å) biquadratic coupling is observed. The amplitude of the giant magnetoresistive effect reaches its maximum value for tCu=12 Å, and values in excess of 4% are still observed for tCu=10 Å. Interface sharpness is shown to be a key parameter for the observation of antiferromagnetic coupling, as well as a large magnetoresistive effect, at very thin copper layers.