Effect of the Oxygen Content on the Metal‒Insulator Transition and on the Spin State of Co3+ Ions in the Layered NdBaCo2O5 + δ Cobaltite (0.37 ≤ δ ≤ 0.65)

• Published in: JETP letters 2022-05, Vol.115 (9), p.531-538
• Main Authors: Solin, N. I., Naumov, S. V.
• Format: Article
• Language: English
• Subjects: Antiferromagnetism; Atomic; Biological and Medical Physics; Biophysics; Condensed Matter; Curie temperature; Ferromagnetism; Molecular; Optical and Plasma Physics; Oxygen; Oxygen content; Particle and Nuclear Physics; Physics; Physics and Astronomy; Quantum Information Technology; Solid State Physics; Spintronics; Transition temperature
• ISSN: 0021-3640; 1090-6487
• DOI: 10.1134/S0021364022100472

The effect of the oxygen content δ in layered NdBaCo 2 O 5 + δ cobaltite, where 0.37 ≤ δ ≤ 0.65, on the metal‒insulator transition, as well as on the magnetic and spin states of Co 3+ , is studied for the first time. An increase in δ reduces the metal‒insulator transition temperature T MI , the antiferromagnetic ordering temperature T N , and the Curie temperature T C by about 100–150 K. For all values of δ, the metal‒insulator transition occurs when the spin state of Co 3+ ions changes from the HS/LS state in the metallic phase to the IS/LS state in the semiconducting phase, whereas with an increase in δ, the spin state of Co 3+ ions changes from the IS/LS to HS/LS state. At δ ~ 0.65, a heavily doped semiconductor–bad metal transition occurs without any change in the spin state of Co 3+ ions. The ferromagnetic behavior of NdBaCo 2 O 5 + δ in the antiferromagnetic phase below T N is interpreted in terms of the metamagnetic model as the effect of the size of the rare earth Nd 3+ ion on the antiferromagnetic state in layered cobaltites.