The Study of Spin-Phonon Interaction Mediated Phase Anomaly in Highly-Strained BiFeO₃ Films
Yen-Chin Huang1*, Yi-De Liou1, Heng-Jui Liu2, Hsin-Hua Lee1, Yi-Chun Chen1, Ying-Hao Chu2
1Department of Physics, National Cheng Kung University, Tainan, Taiwan
2Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan
* presenting author:Yen-Chin Huang,
The crystal symmetries play an important role in determining the physical properties of materials; hence the discovery of tetragonal-like (Cm) and rhombohedral-like (Cc) polymorph in highly strained BiFeO₃ (BFO) opens more multifarious properties and functionalities. In this study, we observe the strong spin-phonon coupling exists in mixed-phase BFO. The phonon contributions of tetragonal-like phase and rhombohedral-like phase can be in-situ distinguished by the combination of the Raman spectroscope and the atomic force microscope at room temperature. Evolution of two phases at low temperature is known from temperature-dependent x-ray diffraction and Raman spectroscopy. Structural phase transitions at around 225 K and 150 K correspond to the tetragonal-like phase and rhombohedral-like phase, respectively. In addition, tetragonal-like phase and rhombohedral-like phase have strong spin interactions through phase boundaries; therefore, the act of spin-phonon coupling induces the structural phase transitions accompanying the variations of spin ordering and two phases change simultaneously. The apparent changes of phonon behaviors under an external magnetic field show that crystal structures can be affected by a magnetic field in mixed-phase BFO films because of the strong spin-phonon coupling.

Keywords: BiFeO3 (BFO), Morphotropic Phase Boundary (MPB), Spin-Phonon Coupling