Mero Rea Divina, Ogawa Kirari, Yamada Shigeki, Liu Hsiang-Lin
Department of Physics, National Taiwan Normal University, Taipei 11677, Taiwan.
Department of Material System Science, Yokohama City University, Yokohama 236-0027, Japan.
ACS Omega. 2021 Aug 23;6(34):22137-22150. doi: 10.1021/acsomega.1c02763. eCollection 2021 Aug 31.
The double perovskite YBaMnO exhibited complex structural, magnetic, and charge/orbital ordering phase transitions. In this paper, we investigated the correlation between the temperature-dependent optical response and complex phase transitions of YBaMnO single crystals through spectroscopic ellipsometry and Raman scattering spectroscopy. The room temperature optical absorption spectrum of YBaMnO revealed three bands of approximately 1.50, 4.05, and 5.49 eV. The lowest optical absorption band was assigned to on-site d-d transitions in Mn ions, whereas the other two optical features were assigned to charge-transfer transitions between the 2p states of O and 3d states of Mn. The room temperature Raman scattering spectrum revealed 25 phonon modes. Notably, the MnO octahedral tilting and bending modes between 360 and 440 cm increased in intensity at temperatures <200 K. Furthermore, several new phonon peaks appeared at temperatures <200 K, which were associated with charge ordering. Additionally, the magnetic order-induced changes were observed in the breathing modes, with reduced intensity of the 620 cm and a substantial enhancement of the 644 cm phonon peaks. The Jahn-Teller mode at approximately 496 cm exhibited strong hardening at temperatures <200 K, which indicated a linear correlation with the square of the magnetic susceptibility and thus revealed the occurrence of spin-phonon coupling. Anomalies in the phonon frequency, line width, and intensity observed near the phase transition temperatures highlighted the importance of lattice-charge-spin interactions in YBaMnO.
双钙钛矿YBaMnO表现出复杂的结构、磁性以及电荷/轨道有序相变。在本文中，我们通过椭圆偏振光谱和拉曼散射光谱研究了YBaMnO单晶的温度依赖光学响应与复杂相变之间的相关性。YBaMnO的室温光学吸收光谱显示出三个约为1.50、4.05和5.49 eV的吸收带。最低的光学吸收带归因于Mn离子的局域d-d跃迁，而另外两个光学特征归因于O的2p态与Mn的3d态之间的电荷转移跃迁。室温拉曼散射光谱显示出25种声子模式。值得注意的是，在温度<200 K时，360至440 cm之间的MnO八面体倾斜和弯曲模式的强度增加。此外，在温度<200 K时出现了几个新的声子峰，这与电荷有序有关。另外，在呼吸模式中观察到了磁有序诱导的变化，620 cm处的强度降低，644 cm处的声子峰大幅增强。约496 cm处的 Jahn-Teller模式在温度<200 K时表现出强烈的硬化，这表明与磁化率的平方呈线性相关，从而揭示了自旋-声子耦合的发生。在相变温度附近观察到的声子频率、线宽和强度异常突出了YBaMnO中晶格-电荷-自旋相互作用的重要性。
