EFFECT OF THE CATIONIC SIZE VARIATION IN THE GMR COMPOUND Pr_(0.7-x)Ho_xSr_(0.3)MnO_3 AND IN THE CHARGE ORDERED COMPOUNDS Pr_(0.5-x)Ho_xSr_(0.5)MnO_3

摘要

Praseodymium manganites doped with holmium Pr_(1-x-y)Ho_xSr_yMnO_3 (x=0-0.1 in steps of 0.2 and y = 0.3, 0.5) have been prepared and characterized by powder X-ray diffraction, ac magnetic susceptibility, dc magnetic susceptibility, dc electrical resistivity ( ΡH=0 and PH=1.2T) and electron microscopy studies. Both series have a pseudotetragonal distorted perovskite like structure (Pbnm space group). Magnetic and electrical properties of the manganites have been investigated and the compositions are ferromagnetic insulators which exhibit small values of negative magnetoresistance. The highest MR ratio (MR=(R_o-R_h)/Ro) of 48% at 152 K for a field of 1.2T for Pr_(0.6)Ho_(0.1)Sr_(0.3)MnO_3. The results emphasize the role played by the dopant holmium. SEM studies show well structured grains which vary with concentration of the dopant. The compounds were found to favour antiferromagnetism with increasing x.