Spin Density Waves and Proximity Effects in Thin Epitaxial Cr Films

Abstract

We have carried out extensive neutron and synchrotron scattering studies to unravel the spin density and charge density waves of the incommensurate antiferromagnetic Cr spin structure in epitaxially grown thin Cr(001) films, including surface and interface effects. These studies show that, unlike bulk Cr, in thin Cr(001) films of less than 300 nm the spin density waves are almost entirely longitudinal with a single wave vector, \( \vec{Q} \), propagating in the out-of-plane direction. A thin ferromagnetic Fe cap layer of only 2–3 nm thickness causes a complete re-orientation of \( \vec{Q} \) from longitudinal out-of-plane to transverse in-plane. This re-orientational transition can be understood in terms of frustration effects at the Fe/Cr interface, introduced by monoatomic high steps and kinks. In very thin Cr(001) layers sandwiched between Fe(001) layers a second re-orientation takes place to a single \( \vec{Q} \), out-of-plane transverse spin density wave with the Cr spins now lying in the plane. When the Cr layer thickness, t Cr , is reduced to smaller than the extension of the spin density modulation wavelength, Λ SDW , the incommensurate spin density wave collapses and becomes commensurate antiferromagnetic. Lateral Cr thickness fluctuations cause the commensurate antiferromagnetic spin structure to break up into domains. These domains, in turn, mediate a strong non-collinear exchange coupling of adjacent Fe layers.