Effect of Zn substitution on para- to ferromagnetic transition temperature in La0.67Ca0.33Mn1-xZnxO3 colossal magnetoresistance materials

Structural, magnetic, and thermal measurements are carried out on the La0.67Ca0.33Mn1-xZnxO3 system with x=0.0-0.50. The structural characterization of the samples is done by Rietveld analysis of their neutron diffraction patterns. Zn substitutes at Mn site isostructurally until x=0.30. Oxygen content remains nearly invariant with x. Magnetic and thermal measurements as well as the electrical resistance show a para- to-ferromagnetic transition at T-p, which decreases with an increase of x. For low Zn concentration (until x=0.075) the decrease dT(p)/dx is smaller than for the larger concentrations of Zn. Relative decrease dT(p)/dx at higher concentrations (x > 0.10) is similar to that observed earlier for the La0.67Ca0.33Mn1-xFexO3 system. For the transition at T-p, the related change of magnetic entropy (Delta S-trs) are calculated from the heat capacity data and indicate that for x=0 the expected value Delta S-trs=12.8 J/mol K is recovered. (C) 2000 American Institute of Physics. [S0021-8979(00)26508-0].