EPR investigations in La0.67Ca0.33MnO3-δ nanoparticles

We present EPR measurements in colossal magnetorezistive La0.67Ca0.33MnO3-δ nanoparticles. The samples with different particle sizes were prepared by sol-gel method followed by heat treatment at different temperatures. The effective crystallite sizes were determined by X-ray profile Fourier analysis. The temperature and particle size dependence of g-factor, the resonance linewidth and the integral intensity have been investigated. Decreasing particle size leads to the decreasing of g-value and of the Curie-Weiss temperature, θ. It appears that larger grain size particles have larger internal fields. In the paramagnetic regime, the temperature dependence of the integral intensity is discussed in terms of the bottlenecked spin-relaxation model. The exchange coupling parameter for Mn3+ and Mn4+ ions shows a decrease with decreasing particle size. (author)