Correlation between structure and magnetic properties of Cd-substituted La0.7(Ca0.3−xCdx)MnO3 CMR manganites
ABSTRACT Structural, electrical and magnetic properties of Cd-doped La0.7(Ca0.3−xCdx)MnO3 (0⩽x⩽0.3) manganites are presented. All compositions were indexed in the orthorhombic (Pnma) space group, except the Cd0.3 sample, indexed as a combination of trigonal and orthorhombic (Pnma) space groups. Substitution of Ca by Cd has a strong influence on the magnetic and magnetoresistive properties of these compounds, continuously decreasing both the magnetic moment and the Curie temperature (from 3.5 μB and 270 K for the x=0 composition to 1.59 μB and 90 K for the fully doped x=0.3 one). Samples corresponding to x=0 and 0.1 show a semiconductor–metal transition at temperatures close to the Curie ones. The measured magnetoresistance change is about 49% at 270 K and 95% at 165 K for those samples, respectively. However, the x=0.2 and 0.3 compositions show insulating behaviour in the whole temperature range studied, with values of the magnetoresistance about 85% at 105 K and 74% at 90 K, respectively. The observed weakening of the double-exchange mechanism as the Cd doping level in these samples increases is discussed in terms of structural properties, cationic disorder and Mn3+/Mn4+content ratio.