Abstract
La 0.8Sr 0.2Co 1− x Fe x O 3 ( x=0.15, 0.2, 0.3) samples were studied by means of AC magnetic susceptibility, magnetization, magnetoresistance and 57Fe Mössbauer spectrometry. Iron was found to take on a high spin 3d 5− α electronic state in each of the samples, where α refers to a partly delocalized 3d electron. The compounds were found to exhibit a spin-cluster glass transition with a common transition temperature of ∼53 K. The spin-cluster glass transition is visualized in the 57Fe Mössbauer spectra as the slowing down of magnetic relaxation below ∼70 K, thereby showing that iron takes part in the formation of the glassy magnetic phase. The paramagnetic-like phase found at higher temperatures is identified below T c≈195 K as being composed of weakly interacting, magnetically ordered nanosized clusters of magnetic ions in part with a magnetic moment oriented opposite to the net magnetic moment of the cluster. For each of the samples a considerable low-temperature negative magnetoresistance was found, whose magnitude in the studied range decreases with increasing iron concentration. The observed results obtained on the present compounds are qualitatively explained assuming that the absolute strengths of magnetic exchange interactions are subject to the relation ∣ J Co–Co∣<∣ J Fe–Co∣<∣ J Fe–Fe∣.
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