Observation of Robust Compressed CuO<sub>6</sub> Octahedra and Exotic Spin Structure in CaCuFe<sub>2</sub>O<sub>5</sub>
Maocai Pi, Junye Yang, Jie Zhang, Xubin Ye, Xiao Wang, Lunhua He, Zhiwei Hu, Chien‐Te Chen, Chang‐Yang Kuo, Zhao Pan, Yao Shen, Youwen Long
Abstract
CuO 6 octahedra usually show elongated distortion, leading to active d x 2 −y 2 orbitals and planar exchange interactions, while compressed CuO 6 octahedra with active d 3 z 2 − r 2 orbitals and unidirectional exchange interactions are exceptionally rare. Here, we design and synthesize a new frustrated antiferromagnet CaCuFe 2 O 5 through a high-pressure and high-temperature approach, in which robust compressed CuO 6 octahedra are realized, separating the Fe 2 O 5 sheets that comprise zigzag spin ladders. Magnetic susceptibility and specific heat measurements exhibit a long-range antiferromagnetic order below the Néel temperature of 165 K, which is further confirmed by neutron diffraction. Detailed magnetic refinement reveals a C-type spin structure, with its spin arrangement and orientation distinct from that of the isostructural CaFe 3 O 5 . By constructing a Heisenberg model, we find that this is due to the exchange redistribution between the CuO 6 octahedra and Fe 2 O 5 sheets, during which some of the exchange interactions are selectively annihilated due to the specific orientation of the Cu d 3 z 2 − r 2 orbitals in the compressed CuO 6 octahedra. Our results provide a unique example of robust compressed CuO 6 octahedra and show that it can selectively annihilate some of the exchange interactions and completely modify the spin structure and magnetic frustration accordingly.