Comparative Studies of Frustrated Cobaltites YBaCo.sub.4O.sub.7 +.sub.x and DyBaCo.sub.4O.sub.7 +.sub.x with Small Oxygen Nonstoichiometry

• Published in: Journal of experimental and theoretical physics 2020-09, Vol.131 (3), p.437
• Main Authors: Kazei, Z. A, Snegirev, V. V, Stolyarenko, M. S
• Format: Article
• Language: English
• Subjects: Anisotropy; Cobalt; Magnetic properties
• ISSN: 1063-7761; 1090-6509
• DOI: 10.1134/S1063776120080014

Comparative experimental studies of the structural and elastic characteristics of the YBaCo.sub.4O.sub.7 +.sub.x and DyBaCo.sub.4O.sub.7 +.sub.x (x = 0, 0.1, 0.2) cobaltite systems reveal their different behavior depending on excess oxygen content x. A relation between structural parameters a.sub.av = (a + b/ [Formula omitted])/2 and c and index x is determined, and the nonstoichiometric cobaltites are found to be separated into two phases with different values of x under certain synthesis and heat-treatment conditions. Stoichiometric samples with Y and Dy ions have ortho-rhombic lattice distortions [epsilon].sub.o = (a - b/ [Formula omitted])/a = -3.9 x 10.sup.-3 and [epsilon].sub.o = -4.1 x 10.sup.-3, respectively. These distortions remove frustrations and promote the formation of a long-range magnetic order in the cobalt subsystem. The Y cobaltite exhibits pronounced anomalies of the elastic properties at the magnetic phase transition temperature T.sub.N, and only their traces are detected in the Dy cobaltite. The structural distortion disappears in the samples of both series at a small oxygen nonstoichiometry, the frustrations are retained, the further development of a long-range magnetic order is hindered, and the anomalies of the elastic properties at T.sub.N are rapidly smeared and disappear. The qualitatively different behavior of the DyBaCo.sub.4O.sub.7 +.sub.x series is likely to be related to the rare-earth-ion-induced magnetic anisotropy.