Lee Seongsu, Pirogov A, Kang Misun, Jang Kwang-Hyun, Yonemura M, Kamiyama T, Cheong S-W, Gozzo F, Shin Namsoo, Kimura H, Noda Y, Park J-G
Department of Physics, SungKyunKwan University, Suwon 440-746, Korea.
Nature. 2008 Feb 14;451(7180):805-8. doi: 10.1038/nature06507.
The motion of atoms in a solid always responds to cooling or heating in a way that is consistent with the symmetry of the given space group of the solid to which they belong. When the atoms move, the electronic structure of the solid changes, leading to different physical properties. Therefore, the determination of where atoms are and what atoms do is a cornerstone of modern solid-state physics. However, experimental observations of atomic displacements measured as a function of temperature are very rare, because those displacements are, in almost all cases, exceedingly small. Here we show, using a combination of diffraction techniques, that the hexagonal manganites RMnO3 (where R is a rare-earth element) undergo an isostructural transition with exceptionally large atomic displacements: two orders of magnitude larger than those seen in any other magnetic material, resulting in an unusually strong magneto-elastic coupling. We follow the exact atomic displacements of all the atoms in the unit cell as a function of temperature and find consistency with theoretical predictions based on group theories. We argue that this gigantic magneto-elastic coupling in RMnO3 holds the key to the recently observed magneto-electric phenomenon in this intriguing class of materials.
固体中原子的运动总是以一种与它们所属固体的给定空间群的对称性相一致的方式对冷却或加热做出响应。当原子移动时，固体的电子结构会发生变化，从而导致不同的物理性质。因此，确定原子的位置以及原子的行为是现代固态物理学的基石。然而，作为温度函数测量的原子位移的实验观测非常罕见，因为在几乎所有情况下，这些位移都极其微小。在这里，我们使用多种衍射技术表明，六方锰酸盐RMnO₃（其中R是稀土元素）经历了一种具有异常大原子位移的同结构转变：比在任何其他磁性材料中观察到的位移大两个数量级，从而导致异常强的磁弹性耦合。我们追踪了晶胞中所有原子的确切原子位移随温度的变化，并发现与基于群论的理论预测一致。我们认为，RMnO₃中这种巨大的磁弹性耦合是这类有趣材料中最近观察到的磁电现象的关键。
