Yili Sun, Yu Huang, Jingwen Cheng, Shanshan Zhang, Z. Li, Huiqian Luo, Xiaobai Ma, Wenyun Yang, Jinbo Yang, Dongfeng Chen, Kai Sun, M. Gutmann, Silvia C. Capelli, Feiran Shen, Jiazheng Hao, Lunhua He, Genfu Chen, Shiliang Li
Altermagnetism has been proposed as a distinct class of antiferromagnets exhibiting momentum-dependent spin splitting band structures without requiring spin-orbit coupling. Recently, ${\mathrm{KV}}_{2}{\mathrm{Se}}_{2}\mathrm{O}$ has been identified as a metallic room-temperature altermagnet with $d$-wave spin-momentum locking. Here, we investigate the magnetic structure of ${\mathrm{KV}}_{2}{\mathrm{Se}}_{2}\mathrm{O}$ in both polycrystalline and single-crystal samples using neutron diffraction techniques. The system exhibits G-type antiferromagnetic structure with a N\'eel temperature ${T}_{N}\ensuremath{\approx}$ 400 K. Notably, substantial broadening of magnetic peaks was observed along $L$ at low temperatures in single crystals, consistent with the coexistence of G-type AFM order and a $c$-axis spin density wave. These results demonstrate that bulk ${\mathrm{KV}}_{2}{\mathrm{Se}}_{2}\mathrm{O}$ cannot host altermagnetism.