Magnetic and phonon transitions in B-site Co doped BiFeO3 ceramics


Yueh-Sheng Chiang, Chi-Shun Tu, Pin-Yi Chen, Cheng-Sao Chen, J. Anthoniappen, Yi Ting, Ting-Shan Chan, V. Hugo Schmidt


Ceramics International


Magnetic susceptibility and phonons have been characterized in multiferroic Bi(Fe1-x Co x )O3-δ ceramics for x=0.0, 0.05, and 0.10 (BFO100xCo) as functions of temperature. A preferred (100) crystallographic orientation and increasing average oxygen vacancies were observed in BFO5Co and BFO10Co. The Fe and Co K-edge synchrotron X-ray absorptions revealed mixed valences of Fe3+, Fe4+, Co2+, and Co3+ ions in BFO5Co and BFO10Co, which exhibit a ferromagnetic (or ferrimagnetic) phase below room temperature due to appearance of ferromagnetic B-O‒B (B=Fe and Co) superexchange interactions. Field-cooled (FC) and zero-field‒cooled (ZFC) magnetic susceptibilities exhibit a significant spin-glass splitting below room temperature in BFO5Co and BFO10Co. Two Raman-active phonon anomalies at ~170K (or 200K) and ~260K were attributed to the Fe3+‒O-Co3+ and Co3+‒O-Co3+ magnetic orderings, respectively. This work suggests that the low-spin Co2+‒O-Co2+, Fe3+‒O-Fe3+ (or Fe4+), and high-spin Co2+‒O-Co2+ superexchange interactions are responsible for phonon anomalies at ~290 (or ~300K), ~400, and ~470K (or ~520K) in BFO5Co and BFO10Co.



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