Magnetic Properties of La 0.7Ca0.3 MnO3 Manganite Bulk and Nanometer-Sized Crystals

AC and DC magnetic measurements in temperature interval 5-300 K and at external magnetic field Hles 5 T were employed to probe and compare magnetic ordering in bulk and nanometer-sized (15plusmn2 nm) La_0.7Ca_0.3MnO₃ single crystals. The respective Curie temperatures (T_C)~239 K and 233 K, close to each other are observed in bulk and nano samples. While, their low T spontaneous magnetizations are strongly different, being about 3.6 and 1.2 mu_B/f.u., respectively. AC susceptibility (chi) of a bulk sample, measured at H_dc=0, shows a maximum of chi(T) at T~T_C. In a contrast, chi(T) of the nano-sample demonstrates a broad maximum far below its T_C. In the nano-sample both real and imaginary parts of chi are frequency dependent within the 5-280 K range. In a contrary, the frequency dependence is observed only for imaginary part of chi in bulk crystal. It is concluded that the similar ferromagnetic ground state exists in both considered samples; however, it is strongly frustrated in agglomerated nano particles due to surface magnetic disorder and interparticle interactions.