Department of Materials Science and Engineering, and Division of Advanced Materials Science, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea.
Phys Rev Lett. 2011 Sep 9;107(11):117201. doi: 10.1103/PhysRevLett.107.117201. Epub 2011 Sep 6.
SmFeO3, a family of centrosymmetric rare-earth orthoferrites, is known to be nonferroelectric. However, we have found that SmFeO3 is surprisingly ferroelectric at room temperature with a small polarization along the b axis of Pbnm. First-principles calculations indicate that the canted antiferromagnetic ordering with two nonequivalent spin pairs is responsible for this extraordinary polarization and that the reverse Dzyaloshinskii-Moriya interaction dominates over the exchange-striction mechanism in the manifestation of the improper ferroelectricity. SmFeO3 further exhibits an interesting phenomenon of spontaneous magnetization reversal at cryogenic temperatures. This reversal is attributed to the activation of the Sm-spin moment which is antiparallel to the Fe-spin moment below ∼5 K.
SmFeO3 是一类中心对称的稀土正铁氧体，通常被认为是非铁电体。然而，我们发现 SmFeO3 在室温下具有沿 b 轴的小极化强度，表现出铁电性，空间群为 Pbnm。第一性原理计算表明，导致这种反常极化的原因是存在两个不等价自旋对的倾斜反铁磁有序，并且反 Dzyaloshinskii-Moriya 相互作用在表现出这种非本征铁电性方面占主导地位，超过了交换弹性机制。SmFeO3 在低温下还表现出自发磁化反转的有趣现象。这种反转归因于 Sm 自旋矩在约 5 K 以下与 Fe 自旋矩反平行的激活。
