Comparative electron magnetic resonance study of magnetic ordering in La_(1-x)Ca_(x)MnO_(3) (x(velence)0.1,0.3) bulk and nanometer sized manganite crystals

摘要

To check the impact of nanosize originated effects on the magnetic ordering in doped manganites, X-band electron magnetic resonance measurements were performed in 5 K <= T <= 600 K interval on nanometer sized and bulk crystals of La_(1-x)Ca_(x)MnO_(3) (x(velence)0.1,0.3). The analysis of electron paramagnetic resonance parameters together with the data of magnetic measurements shows that bulk La_(0.9)Ca_(0.1)MnO_(3) is characterized by inhomogeneous confinement of charge carriers, leading to its mixed magnetic ordering. The nanocrystals of the same composition show the carrier mobility within impuritylike band, which induces ferromagneticlike ground state. The bulk La_(0.7)Ca_(0.3)MnO_(3) demonstrates homogeneous ferromagnetism and bandlike carriers mobility. The surface magnetic disorder in its nanocounterpart leads to appearance of two magnetic phases--core phase (bulklike in properties) and a surface one with notably reduced temperature of magnetic ordering. It appears that neither double exchange interaction nor carrier mobility exists between these phases.