Effects of Oxygen Content on Bi₃Mn₃O_11+δ: From 45 K Antiferromagnetism to Room-Temperature True Ferromagnetism

Abstract

The effects of oxygen content on the structural, physical, and chemical properties of Bi3Mn3O11 with KSbO3-type structure have been investigated. It was found that the oxygen content in Bi3Mn3O11+δ can vary over a wide δ range, keeping the same cubic structure (space group Pn3̅, a = 9.12172(5) Å for δ = −0.5, a = 9.13784(8) Å for δ = 0, and a = 9.09863(7) Å for δ = 0.6) and semiconducting properties of the material. At the same time, magnetic properties change from true antiferromagnetic with TN = 45 K for δ = −0.5 to true ferromagnetic with TC = 307 K for δ = +0.6. Bi3Mn3O11 (δ = 0) shows ferrimagnetic-like properties with TC = 150 K and features typical for a re-entrant spin-glass below 30 K. Noticeable changes of the magnetic transition temperature and magnetism in Bi3Mn3O11+δ with δ can be compared with changes of the magnetic and electronic properties of LaMnO3+δ, BiMnO3+δ, high-temperature copper superconductors (e.g., YBa2Cu3O7+δ), and other cuprates. Bi3Mn3O11.6 shows a new record high TC among insulating/semiconducting true ferromagnets. Our results demonstrate that the oxygen content can vary for the same cation composition in KSbO3-type materials, and the oxygen content can be increased up to BiMnO3.867 (Bi3Mn3O11.6)