MAGNETIC PHASE-DIAGRAM FOR SPIN-DENSITY WAVES IN THIN EPITAXIAL CR(001) FILMS

We have investigated the magnetic structure of thin [0 0 1] oriented C r films using neutron and X-ray diffraction experiments to measure the ir spin density waves and the strain waves, respectively. For epitaxia l Cr films with thicknesses between 1000 and 4000 Angstrom grown on Nb films on sapphire substrates, we provide phase diagrams including inc ommensurate transverse and longitudinal spin-density waves (SDW) as we ll as commensurate antiferromagnetic spin structures. The results show that for Cr(0 0 1) on Nb a single domain SDW prevails with a wave vec tor Q perpendicular to the surface. At low temperatures the SDW is lon gitudinal and becomes mostly transverse between 150 and 250 K, higher than in bulk Cr where the spin-Aip transition occurs at 123 K. Further more, the magnitude of Q is increased as compared to bulk Cr, These ef fects decrease with increasing film thickness. With neutron scattering we have also observed a commensurate antiferromagnetic phase with spi ns pointing out of the plane. The commensurate phase occurs at a tempe rature between 250 and 305 K and persists up to at least 340 K, far ab ove the bulk Neel temperature of 311 K for the incommensurate phase. ( C) 1998 Elsevier Science B.V. All rights reserved.