Antiferromagnetic structure of KV 2 Se 2 O : A neutron diffraction study

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.