Local structure and magnetic properties of Mn substituted manganites studied by EXAFS and Dc magnetic measurements

摘要

We report extended X-ray absorption fine structure (EXAFS) measurements at the Mn K edge and magnetic measurements performed on (La1-xCax)(Mn1-yMy)O-3 samples (M=Cr or Ni; x=0.37 and 0.75 and y=0.03 or 0.08). The Mn substitution produces important effects on both the sides of the LaMnO3-CaMnO3 phase diagram. For x < 0.5 the ferromagnetic-metallic phase maintains its main character even after Mn substitution, but both the doping species (Ni or Cr) lower T-C and broaden the magnetic transition, and the EXAFS study evidences two Mn-O distances, suggesting the presence of zones of distorted insulating phase. For x > 0.5, after the doping with Cr, the charge ordered phase persists but on a shorter scale, whereas the Jahn-Teller distortion is weakened as indicated by EXAFS measurements, and the formation of ferromagnetic clusters is evidenced by magnetic measurements.EXAFS and magnetic measurements are in mutual agreement, thus confirming the correlation between the local disorder determined by charge localization and magnetic degrees of freedom. (C) 2005 Elsevier Ltd. All rights reserved.