La 0.7 Ca 0.3 MnO 3 (LCMO) nanoparticles were synthesized by reactive milling in ambient conditions. Magnetic properties of LCMO single-phase nanocrystalline particles were studied. LCMO nanoparticles exhibit superparamagnetism with blocking temperature that decreases in the logarithmic function as increasing applied magnetic field. Besides, the blocking temperature decreases as increasing milling time from 8h to 16h. The temperature dependence of the saturation magnetization shows a strong collective excitation due to the spin wave that depends on temperature in form T α with α=1.7, which slightly deviates from the Bloch law.