The spatial extent ${\zeta }_{\mathrm{AFM}}$ and strength $J_{\mathrm{AFM}}$ of the antiferromagnetic (AFM) exchange coupling at buried Gd $/$Fe interfaces in ferrimagnetic $\left[\mathrm{Gd}\right(50Å\left)\mathrm{Fe}\right(15,35Å){]}_{15}$ sputtered multilayers is obtained from combined x-ray resonance magnetic reflectivity and magnetic circular dichroism measurements. ${\zeta }_{\mathrm{AFM}}$ is $4.1\left(7\right)Å$ or $\sim 1–2$ interatomic distances in bulk Gd and Fe; $J_{\mathrm{AFM}}$ is 1050(90) K, comparable to the ferromagnetic exchange in bulk Fe.

• Received 2 August 2001

DOI:https://doi.org/10.1103/PhysRevLett.87.207201