Correlation of short-period oscillatory exchange coupling to nanometer-scale lateral interface structure in Fe/Cr/Fe(001)

We investigate Fe/Cr/Fe(001) trilayers grown on Ag(001)/Fe/GaAs(001) substrates at different temperatures. By changing the substrate temperature of the bottom Fe film during deposition, but otherwise keeping the preparation parameters constant, we are able to tailor the roughness of the Fe/Cr interfaces. The interfaces are characterized by means of scanning tunneling microscopy (STM). In these differently prepared systems, a clear change of the short-period oscillation amplitude is observed by magneto-optical Kerr effect measurements. A statistical analysis of the STM images allows us to extract the lateral length scale over which the Cr thickness is constant, and it turns out that areas of constant Cr thickness with a diameter larger than $3–4\hspace{0.5em}\mathrm{nm}$ are mandatory for the evolution of short-period oscillations. Two mechanisms are discussed which can explain the observed correlation between structure and magnetism, one linked to the propagation of the coupling through the spacer and the other to the response of the ferromagnetic layers to the transmitted exchange field.