Strong Ferromagnetism Achieved via Breathing Lattices in Atomically Thin Cobaltites

Published

January 27, 2021

Author(s)

Sisi Li, Qinghua Zhang, Shan Lin, Xiahan Sang, Ryan F. Need, Manuel A. Roldan, Wenjun Cui, Zhiyi Hu, Qiao Jin, Shuang Chen, Jiali Zhao, Jia-Ou Wang, Jiesu Wang, Meng He, Chen Ge, Can Wang, Hui-Bin Lu, Zhenping Wu, Haizhong Guo, Xin Tong, Tao Zhu, Brian Kirby, Lin Gu, Kui-juan Jin, Er-Jia Guo

Abstract

Low-dimensional quantum materials that retain strong ferromagnetism down to monolayer thickness hold great potential for spintronic applications. However, ferromagnetism in the transition metal oxides decays severely when the thickness is scaled to the nanometer regime, leading to deterioration of device performance. Here we report a methodology for maintaining strong ferromagnetism in LaCoO₃ (LCO) ultrathin layers with a thickness of a single unit cell. We find that the magnetic and electronic states of LCO are intimately linked to the structural parameters of adjacent SrCuO₂ (SCO). With reduction of the SCO thickness below five-unit-cells, the oxygen coordination of the Cu²⁺ ions transforms from the planar-type to chain-type and is accompanied by a huge elongation of the unit cell along the growth direction. The ultrathin LCO layers respond the structural change in SCO via its own structural modulation, namely, a distortion of the CoO₆ octahedra characterized by significant reduction of the bond angle and elongation of the bond length. In turn, this structural modulation in LCO reduces the crystal field splitting energy and promotes a higher spin state and long-range order of the cobalt ions, resulting in an unexpected large magnetization, which presents the highest value in any monolayer oxides. Our results demonstrate a strategy for creating ultrathin ferromagnetic oxides by exploiting atomic heterointerface engineering, confinement-driven structural transformation, and spin-lattice entanglement in strongly correlated materials.

Citation

Advanced Materials

Volume

33

Issue

4

Pub Type

Journals

Keywords

oxide films, magnetism

Citation

Li, S. , Zhang, Q. , Lin, S. , Sang, X. , Need, R. , Roldan, M. , Cui, W. , Hu, Z. , Jin, Q. , Chen, S. , Zhao, J. , Wang, J. , Wang, J. , He, M. , Ge, C. , Wang, C. , Lu, H. , Wu, Z. , Guo, H. , Tong, X. , Zhu, T. , Kirby, B. , Gu, L. , Jin, K. and Guo, E. (2021), Strong Ferromagnetism Achieved via Breathing Lattices in Atomically Thin Cobaltites, Advanced Materials (Accessed April 26, 2024)