Abstract
Magnetotransport properties, magnetization, AC susceptibilities and electron spin resonance (ESR) were measured to investigate internal spin dynamics of cobaltites La 1− x Sr x CoO 3 ( x = 0.1 , 0.2 , 0.3 ). Semiconducting behavior for x = 0.1 , 0.2 and semiconducting-metallic transition for x = 0.3 at ∼120 K were observed. With increasing Sr doping, the Curie temperature ( T C) increases. The spin-glass and cluster-glass behaviors were confirmed through the frequency-dependent AC susceptibility. ESR spectra of the samples in the temperature range studied could be divided into three regimes corresponding to different linewidths. This feature is due to both the presence of an anisotropic field arising from ferromagnetic clusters and the variation of spin-state transitions of Co ions. Lorentzian ESR signals at temperatures T< T min become Gaussian at T> T min. In a fashion similar to manganites, the peak-to-peak ESR linewidth vs. temperature, Δ H pp( T), for samples has a minimum value at temperature T min = ∼ 1.7 T C . To explain the physical mechanisms occurring in the samples, resistivity, AC susceptibility and Δ H pp( T) data were analyzed in detail.
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