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

Proximity effects of 20 Å 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 $\mathbf{Q}$ pointing along only one $\{100\}$ direction which depends dramatically on the film thickness $t_{\mathrm{Cr}}$. For $t_{\mathrm{Cr}}<250\mathrm{}Å$ the SDW propagates out of plane with the spins in the film plane. For $t_{\mathrm{Cr}}>1000\mathrm{}Å$ 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.