Enhanced ferromagnetic transition temperature in nanocrystalline lanthanum calcium manganese oxide (La0.67Ca0.33MnO3)

We report a novel, low temperature (450–600 °C) route for the synthesis of highly crystalline and homogeneous nanoparticles of lanthanum calcium manganese oxide La0.67Ca0.33MnO3 (LCMO). The nanocrystallites, with average particle size of 30 nm, possess a ferromagnetic–paramagnetic transition temperature (Tc) of 300 K, which is about 50 K higher than that of a bulk single crystal. The transition temperature was found to be inversely proportional to the particle size. The Rietveld analysis of the powder X-ray diffraction data of the phase-pure nanopowders reveals that the particle size reduction leads to a significant contraction of the unit cell volume and a reduction of the unit cell anisotropy. We propose that these two lattice effects are responsible for the observed enhancement in Tc.