Specific effects of nanometer scale size on magnetic ordering in La1−xCaxMnO3 (x = 0.1, 0.3 and 0.6) manganites

To check the impact of nano-size originated effects on the magnetic ordering in doped manganites, X-band electron magnetic resonance measurements were performed on nanometer sized and bulk samples of La1−xCaxMnO3 (x = 0.1, 0.3 and 0.6). The model fittings of EPR signal parameters and complementary magnetic measurements indicate that bulk La0.9Ca0.1MnO3 shows inhomogeneous confinement of charge carriers, leading to its mixed magnetic ordering. The carriers mobility within impurity-like band and ferromagnetic (FM)-like ground state are observed on nanocrystals of the same composition. The bulk La0.7Ca0.3MnO3 demonstrates homogeneous FM order and band-like carrier mobility. The surface magnetic disorder in its nano-counterpart leads to appearance of two magnetic phases – a core phase (bulk-like in properties) and a surface phase with notably reduced temperature of magnetic ordering; neither double-exchange interaction nor carriers mobility exist between these phases. The size reduction induced effects in La0.4Ca0.6MnO3 are: an increase of surface FM-like component and a decrease of the charge-ordering temperature. These findings allow us to conclude that the nano-scale effect on magnetic ordering in La1−xCaxMnO3 system weakens progressively upon stabilization of the low temperature magnetic ground state with Ca-doping.