Polarized neutron reflectivity studies of biquadratic coupling in [Fe/Cr] (100) and [Fe/Al] (100) superlattices and films (invited) (abstract)

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Sensitivity to magnetic atoms and low intrinsic absorption characterize the interaction of neutrons with matter. Consequently, polarized neutron reflectivity provides a unique means of performing depth-resolved vector magnetometry. We have used this technique to determine the magnetization depth profiles of Fe/Cr superlattices. Superlattices of bilayer composition [55 Å Fe/17 Å Cr], grown at 523 K, exhibit biquadratic coupling with large saturation fields (~3 kOe), while those grown at 293 K are ferromagnetically ordered. We have directly measured the evolution of the coupling angle between adjacent Fe layers as a function of applied field and will discuss how bilinear, biquadratic, and external field terms produce the observed order. The weaker coupling found in the Fe/Al system makes possible the investigation of a range of spin configurations at temperatures that do not endanger the sample. We have mapped the phase diagram of a [42 Å Fe/12 Å Al/39 Å Fe] (100) trilayer and find evidence of biquadratic coupling at low temperatures and fields (e.g., when H=180 Oe, the Fe layer spins relax away from ferromagnetic alignment below T170 K). Our measurements agree qualitatively with energy minimization calculations and the results of bulk magnetometry. Journal of Applied Physics is copyrighted by The American Institute of Physics.