Magnetic phase diagram for spin-density waves in thin epitaxial Cr(0 0 1) films

Abstract

We have investigated the magnetic structure of thin [0 0 1] oriented Cr films using neutron and X-ray diffraction experiments to measure their spin density waves and the strain waves, respectively. For epitaxial Cr films with thicknesses between 1000 and 4000 Å grown on Nb films on sapphire substrates, we provide phase diagrams including incommensurate transverse and longitudinal spin-density waves (SDW) as well as commensurate antiferromagnetic spin structures. The results show that for Cr(0 0 1) on Nb a single domain SDW prevails with a wave vector Q perpendicular to the surface. At low temperatures the SDW is longitudinal and becomes mostly transverse between 150 and 250 K, higher than in bulk Cr where the spin–flip transition occurs at 123 K. Furthermore, the magnitude of Q is increased as compared to bulk Cr. These effects decrease with increasing film thickness. With neutron scattering we have also observed a commensurate antiferromagnetic phase with spins pointing out of the plane. The commensurate phase occurs at a temperature between 250 and 305 K and persists up to at least 340 K, far above the bulk Néel temperature of 311 K for the incommensurate phase.