Behavior of Cobalt and Rare-Earth Subsystems in Frustrated Cobaltites DyBaCo4O7 + x

Resumo

Structural, elastic, and magnetic properties of cobaltites DyBaCo₄O_7 + x produced by various technologies and distinguished by oxygen excess x are experimentally studied. It was found that rhombic distortion of the crystal structure of annealed stoichiometric samples with x = 0 results in frustration removal and elastic property anomalies in the T_N region, caused by cobalt subsystem ordering. At an insignificant oxygen nonstoichiometry, no structural distortions occur in quenched samples, and anomalies in elastic characteristics in the T_N region smooth and disappear. The studies of DyBaCo₄O_7 + x magnetic properties show that the rare-earth (RE) subsystem remains paramagnetic and its contribution exceeds the contribution of the Co-subsystem with strong antiferromagnetic couplings by an order of magnitude. The magnetic susceptibility of the stoichiometric sample does not exhibit an appreciable anomaly at T_N, since cobalt subsystem ordering is not accompanied by the formation of a noticeable effective field on RE ions.