Reorientation of Spin Density Waves in Cr(001) Films induced by Fe(001) Cap Layers

Proximity effects of $20 \mathrm \AA$ thin Fe layers on the spin density waves (SDWs) in epitaxial Cr(001) films are revealed by neutron scattering. Unlike in bulk Cr we observe a SDW with its wave vector ${\bf Q}$ pointing along only one {100} direction which depends dramatically on the film thickness $t_{\mathrm{Cr}}$. For $t_{\mathrm Cr} < 250 \mathrm \AA$ the SDW propagates out-of-plane with the spins in the film plane. For $t_{\mathrm Cr} > 1000 \mathrm \AA$ the SDW propagates in the film plane with the spins out-of-plane perpendicular to the in-plane Fe moments. This reorientation transition is explained by frustration effects in the antiferromagnetic interaction between Fe and Cr across the Fe/Cr interface due to steps at the interface.