Magnetic resonance in crystalline La0.9Ca0.1MnO3: Comparative study of bulk and nanometer-sized samples

X-band electron magnetic resonance (EMR) measurements were done at 115⩽T⩽600 K on bulk and nanometer size-grain powder single-crystalline samples of La0.9Ca0.1MnO3, in order to study an impact of structural inhomogeneity on magnetic ordering. For the nano-crystal sample, two superimposed EMR lines are observed below 240 K, while for bulk-crystal one, a second line emerges in narrow temperature interval below 130 K. Temperature dependences of resonance field and line width of the main and the secondary line are drastically different. EMR data and complementary magnetic measurements of bulk-crystal sample reveal mixed-magnetic phase, which agrees with the published phase diagram of bulk La1−xCaxMnO3. In a marked contrast, the same analysis for nano-crystal sample shows two phases one of which is definitely ferromagnetic (FM) and other is likely such, or super paramagnetic. The data obtained are interpreted in terms of very different magnetic ground states in the two samples, that is attributed to different randomness of the indirect FM exchange interactions mediated by bound holes.