Antiferromagnet–ferromagnet transition in the cobaltites

• Published in: Физика низких температур
• Date: 2012
• Main Authors: Troyanchuk, I.O., Bushinsky, M.V., Karpinsky, D.V., Sirenko, V.A.
• Format: Article
• Language: English
• Published: Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України 2012
• Subjects: Магнетизм
• Online Access: https://nasplib.isofts.kiev.ua/handle/123456789/117271
• Journal Title: Digital Library of Periodicals of National Academy of Sciences of Ukraine
• Cite this: Antiferromagnet–ferromagnet transition in the cobaltites / I.O. Troyanchuk, M.V. Bushinsky, D.V. Karpinsky // Физика низких температур. — 2012. — Т. 38, № 7. — С. 833-841. — Бібліогр.: 53 назв. — англ.

The three series oxygen-deficient cobaltites La₀.₅Ba₀.₅CoO₃₋δ, LnBaCo₂O₅.₅ and Sr₂YCo₄O₁₀.₅ have been studied. It has been shown that La₀.₅Ba₀.₅CoO₃ is an insulating ferromagnet whereas La₀.₅Ba₀.₅CoO₂.₇₅ is a pure antiferromagnet in which the oxygen vacancies are disordered. The oxygen-vacancies ordering leads to appearance of the ferromagnetic component apparently due to a formation of the noncollinear magnetic structure. The antiferromagnet–“ferromagnet” transition is accompanied by a giant magnetoresistance. It is suggested that in the ferromagnetic oxidized compounds Co³⁺ and Co⁴⁺ ions adopt intermediate spin state whereas for antiferromagnetic (Co⁴⁺-free) compositions Co³⁺ ions have high-spin state (pyramids CoO₅) and dominant low-spin state (octahedra CoO₆). In both ferromagnetic and antiferromagnetic compounds the superexchange via oxygen plays an essential role in a formation of the magnetic properties.