Crystal structures and giant magnetoresistance of fluoride La2/3Ca1/3MnO3 compounds

The crystal structures and giant magnetoresistance of CaF2-doped La2/3Ca1/3 MnO3 compounds are investigated by means of X-ray powder diffraction (XRD) and magnetic measurements. The Rietveld powder diffraction profile fitting technique is employed to refine the crystal structures. The results indicat e that the space group of all these compounds is Pbnm, with Z=4. In each un it cell, the 4a, 4c, 4c, and 8d crystal positions are occupied by Mn ions, I,a ions, O-I, and O-II anions, respectively. The F atoms substitute for th e O atoms in the 8d crystal position. The Curie temperatures of these compo unds are enhanced slightly by adding CaF2, and the giant magnetoresistance (GMR) ratios are higher than 67.6% in an applied field of 5 T. (C) 2000 Els evier Science S.A. All rights reserved.