Layered magnetic structures: Evidence for antiferromagnetic coupling of Fe layers across Cr interlayers

Double layers of (100)-oriented Fe with an individual thickness of ≊100 Å, separated by interlayers of Cr or Au with variable thickness were grown epitaxially on Au (100) surfaces. The spin-wave mode spectra of these double layers as detected by means of light scattering were used to measure the effective exchange coupling of the Fe films across the interlayer. For Au interlayers it decreases monotonically with increasing Au thickness dAu and disappears at dAu≳20 Å. For Cr interlayers of proper thickness dCr, i.e., 4 Å≲dCr≲9 Å we obtain antiferromagnetic coupling of the Fe layers. In small external fields such double layers order antiparallel with their magnetization perpendicular to the external field in analogy to the spin-flop phase of antiferromagnets. This is revealed by the behavior of the static magnetization of such samples as a function of external field and the spectrum of spin-wave modes with the wave vector parallel to a small external field.