Low Temperature Physics: 38, 662 (2012); https://doi.org/10.1063/1.4736615 (7 pages)
Физика Низких Температур: Том 38, Выпуск 7 (Июль 2012), c. 833-841    ( к оглавлению , назад )

Antiferromagnet–ferromagnet transition in the cobaltites

I.O. Troyanchuk, M.V. Bushinsky, and D.V. Karpinsky

Scientific-Practical Materials Research Centre of NAS of Belarus, 19 P. Brovka Str., Minsk 220072, Belarus

V.A. Sirenko

B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine, 47 Lenin Ave., Kharkov 61103, Ukraine
E-mail: sirenko@ilt.kharkov.ua

Received March 13, 2012


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.

PACS: 75.50.Dd Nonmetallic ferromagnetic materials;
PACS: 75.30.–m Intrinsic properties of magnetically ordered materials;
PACS: 75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects.

Key words: antiferromagnet, oxygen vacancies, spin state transition, layered perovskite.