On the modulated structure of La2Co1.7: a neutron Laue diffraction study

A preliminary analysis is presented of neutron Laue diffraction data from a single crystal of La2Co1.7 at temperatures between 295 and 15 K, recorded on neutron-sensitive image plates using a thermal neutron beam. The data ca n be interpreted in terms of a charge (nuclear) density wave with a propaga tion vector q(n) = (q(x), 0, q(z)) with q(x) = 0.113(1)a* and q(z) = 0.203( 2)c*. It has also been confirmed by using a band-pass filter with a cold ne utron beam that antiferromagnetic Bragg reflections which have a magnetic p ropagation vector q(m) =(1/3, 1/3, 0) exist below 144(1)K and correspond to a cobalt atom moment of 0.80(15) mu(B). Magnetic satellite reflections wit h wave vectors corresponding to q(n) +/- q(m) have also been observed on th e Lane diagrams below this temperature. The values of the propagation vecto r and magnetic moment have been confirmed from neutron powder diffraction d iagrams taken at 150 and 1.5 K. (C) 2000 Elsevier Science B.V. All rights r eserved.