Biquadratic exchange in ferromagnetic/nonferromagnetic sandwiches: A spin-polarized low-energy electron microscopy study

The magnetic domain structure of Co/Au/Co sandwich layers grown on W(110) is studied in situ by spin-polarized low energy electron microscopy as a function of Au spacer layer and top Co layer thickness with the goal to better understand the causes and consequences of biquadratic coupling for the resulting domain structure. It is found that biquadratic coupling not only strongly influences the coupling between the layers near the zero of the bilinear coupling but also at spacer thicknesses at which strong ferromagnetic coupling occurs. Biquadratic coupling appears in a spin reorientation transition between 4 and 5 monolayers. The existence of bilinear and biquadratic coupling produces a wrinkled in-plane magnetization. [S0163-1829(99)05601-5].