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

The crystal structures and giant magnetoresistance of CaF2-doped La2/3Ca1/3MnO3 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 indicate that the space group of all these compounds is Pbnm, with Z=4. In each unit 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 the O atoms in the 8d crystal position. The Curie temperatures of these compounds 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 Elsevier Science S.A. All rights reserved.