Magnetism of crystalline and amorphous La0.67Ca0.33MnO3 nanoparticles

We report the ferromagnetism of La0.67Ca0.33MnO3 in bulk polycrystalline, nanocrystalline, and amorphous phases. The structural change from crystalline phase to amorphous phase exhibited a systematic decrease in T-C (paramagnetic to ferromagnetic transition temperature) and spontaneous magnetization (M-S). The experimental results suggested few more interesting features, e. g., appearance of large magnetic irreversibility in the temperature dependence of magnetization, lack of magnetic saturation at high magnetic field, blocking of magnetization below T-B, and enhancement of coercivity. In addition, the magnetic phase transition near to T-C changes from first order character in bulk sample to second order character in nanocrystalline and amorphous samples. We understand the observed magnetic features as the effects of decreasing particle size and increasing magnetic (spin-lattice) disorder. The magnetic dynamics of amorphous samples is distinctly different from the nanocrystalline samples and also found to be comparable with the properties of reported amorphous ferromagnetic nanoparticles. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3138814]