TOF neutron powder diffraction study of the helimagnetic structures in theCrxFe1-xVO4-I system

The use of cold neutrons for long d-spacing time-of-flight neutron diffract ion allows high-resolution data to be obtained for the solution and RietveI d refinement of complex magnetic structures. We have used the OSIRIS diffra ctometer at ISIS to collect data for CrxFe1-xVO4-I compounds with x = 0.30, 0.35, 0.40 and 0.45 down to 2 K. The compounds order with a helimagnetic s tructure indexed by a propagation vector (0, k(y), 1/2), analogous to the p reviously reported x = 0.25 and 0.50 samples. Our Rietveld refinements show that ii, varies as a smooth function of x. which indicates that the struct ures are not locked into simple commensurate configurations. An alteration of the moment directions in the models reported for the x = 0.25 and 0.50 m agnetic structures was necessary in order to account for this high-resoluti on data. (C) 2000 Elsevier Science B.V. All rights reserved.