The sawtooth lattice shares some structural similarities with the kagome lattice and may attract renewed research interest. Here, we report a comprehensive study on the physical properties of Fe2SiSe4, an unexplored member in the olivine chalcogenides with the sawtooth lattice of Fe. Our results show that Fe2SiSe4 is a magnetic semiconductor with band gap of 0.66~eV. It first undergoes an antiferromagnetic transition at Tm1=110~K, then an ferrimagnetic-like one at Tm2=50~K and finally a magnetic transition at Tm3=25~K which is likely driven by the thermal populations of spin-orbit manifold on the Fe site. Neutron diffraction analysis reveals a non-collinear antiferromagnetic structure with propagation vector q1=(0,0,0) at Tm2<T<Tm1. Interestingly, below Tm2, an additional antiferromagnetic structure with q2=(0,0.5,0) appears and Fe2SiSe4 exhibits a complex double-q magnetic structure which has never been observed in sawtooth olivines. Density functional theory calculations suggest this complex noncollinear magnetic structure may originate from the competing antiferromagnetic interactions for both intra- and inter-chain in the sawtooth lattice. Furthermore, band structural calculations show that Fe2SiSe4 has quasi-flat band features near the valence and conduction bands. Based on the above results, we propose Fe2SiSe4 as a new material platform to condensed matter researches.
@article{arxiv.2303.13224,
title = {Multiple magnetic transitions and complex magnetic structures in Fe$_2$SiSe$_4$ with the sawtooth lattice},
author = {Feihao Pan and Xunwu Hu and Jiale Huang and Bingxian Shi and Jinchen Wang and Juanjuan Liu and Hongxia Zhang and Daye Xu and Hongliang Wang and Lijie Hao and Peng Cheng and Dao-Xin Yao},
journal= {arXiv preprint arXiv:2303.13224},
year = {2023}
}