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Defect-engineered Fe0.9Co0.1NbO4-δ ceramics: Oxygen vacancy-mediated magnetic behavior and phase stability
Authors: Raí F. Jucá; Diego S. Evaristo;Bruno J.C. Vieira; João C. Waerenborgh; Ana C. Silva; I. Orue; Fernando Plazaola; João M. Soares; Gilberto D. Saraiva; João G. de Oliveira Neto; Nilson S. Ferreira; Marcelo M. Macêdo; José A. Paixão; Benilde F.O. Costa
Ref.: Ceram. Int. 52(11), 16263-16272 (2026)
Abstract: In this work, we investigated the structural, spectroscopic and magnetic properties of 10% cobalt-doped iron niobate (Fe0.9Co0.1NbO4-delta) synthesized by the solid-state reaction method. X-ray photoelectron spectroscopy (XPS) revealed the coexistence of Co2+/Co3+ species and an increased concentration of oxygen vacancies, indicating charge-compensation mechanisms. Electron paramagnetic resonance (EPR) measurements evidenced the presence of Co2+ (3d(7), S-4(3/2)) in octahedral symmetry, Fe3+-O-Co2+ superexchange interactions, and the development of short-range magnetic correlations. M & ouml;ssbauer spectroscopy confirmed the predominance of Fe3+ ions in octahedral coordination and a partial suppression of the Morin transition in residual hematite. Magnetic measurements showed an antiferromagnetic transition at T-N similar to 40 K, along with ferromagnetic contributions arising from Co-doping and oxygen vacancies. Finally, heat-capacity analysis corroborated the second-order character of the magnetic transition, with magnetic entropy values consistent with the expected contributions from Fe3+ (S = 5/2) and Co2+ (S = 3/2) cations.
