$3d$ flat bands and coupled $4f$ moments in the kagome-honeycomb permanent magnet Sm$_{2}$Co$_{17}$

Hao Zheng; Zhiguang Xiao; Ze Pan; Guowei Yang; Yonghao Liu; Jianzhou Bian; Yi Wu; Teng Hua; Jiawen Zhang; Jiayi Lu; Jiong Li; Tulai Sun; Yu Song; Ruihua He; J. Larrea Jiménez; Guanghan Cao; Huiqiu Yuan; Yuanfeng Xu; Yi Yin; Ming Shi; Chao Cao; Yang Liu

arXiv · 2503.12890

$3d$ flat bands and coupled $4f$ moments in the kagome-honeycomb permanent magnet Sm$_{2}$Co$_{17}$

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Abstract

Rare earth permanent magnets (REPMs) with both localized moments and itinerant conduction bands are not only important for fundamental research but also have significant technological applications. In particular, Sm$_{\rm 2}$Co$_{\rm 17}$ is a prototypical high-temperture REPM, where the Co atoms form a kagome-honeycomb stacked lattice. Here we report synthesis of epitaxial Sm$_{\rm 2}$Co$_{\rm 17}$ films using molecular beam epitaxy and measurements of their momentum-resolved electronic structure from \textit{in-situ} angle-resolved photoemission spectroscopy. Our results unveil two flat bands from Co $3d$ orbitals near the Fermi level ($E_F$), one at $\sim$\,--300\,meV and another right at $E_F$, which arise from orbital-selective destructive interference and strong electron correlations, respectively. In addition, our results reveal that Sm $4f$ states are far away from $E_F$ (hence mostly localized) and exhibit an anomalous temperature dependence, caused by the $3d$-$4f$ magnetic coupling. Our findings provide direct spectroscopic insights to understand the strong uniaxial ferromagnetism in Sm$_{\rm 2}$Co$_{\rm 17}$ (and REPMs alike). Our work also opens avenues to explore flat-band physics near $E_F$ and emergent phenomena in correlated kagome-honeycomb lattices.

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Hao Zheng, Zhiguang Xiao, Ze Pan, Guowei Yang, Yonghao Liu, Jianzhou Bian, Yi Wu, Teng Hua, Jiawen Zhang, Jiayi Lu, Jiong Li, Tulai Sun, Yu Song, Ruihua He, J. Larrea Jiménez, Guanghan Cao, Huiqiu Yuan, Yuanfeng Xu, Yi Yin, Ming Shi, Chao Cao, Yang Liu. 2025-03-17. $3d$ flat bands and coupled $4f$ moments in the kagome-honeycomb permanent magnet Sm$_{2}$Co$_{17}$. https://arxiv.org/abs/2503.12890

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