Spin-lattice coupling phase transition and phonon anomalies in bismuth ferrite BiFeO3


Cheng-Sao Chen, Chi-Shun Tu, Pin-Yi Chen, V. Hugo Schmidt, Zhe-Rui Xu, Yi Ting


Journal of Alloys and Compounds


Phase transition, phonon vibration, and magnetization in (100) BiFeO3 (BFO) multiferroic single crystals have been characterized as functions of temperature. The BFO single crystal exhibits a weak ferromagnetic hysteresis loop possibly due to appearance of ferromagnetic Fesingle bondOsingle bondFe orderings and a modulation of the Fesingle bondOsingle bondFe bond. Zero-field-cooled (ZFC) and field-cooled (FC) magnetic susceptibilities suggest a weak spin-glass behavior below ∼200 K. High-resolution transmission electron microscopy (HRTEM) suggests a rhombohedral R3c symmetry (with tilted FeO6 octahedra) and lattice distortion in the surface layer. The BFO crystal undergoes a structural transition sequence of rhombohedral−tetragonal−orthorhombic− cubic at ∼620–640, ∼1000, and ∼1100 K, respectively. The spin-lattice coupling accounts for the rhombohedralsingle bondtetragonal transition upon approaching the Néel temperature (TN). The low-frequency Raman-active modes ψ4,II, E(1), A1(1), and A1(2) reveal clear softening anomalies in frequency shifts and broad peaks in full-width-at-half-maximum (FWHM) around 450 K, which is attributed to the Fesingle bondOsingle bondFe ordering transition without change of structural symmetry.



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