NMR Determination of the Low-Field Magnetic Structure of the Cu-Based Mineral Rouaite Cu${}_2$(OH)${}_3$NO${}_3$

Frustrated interactions in the Cu-based mineral rouaite with alternating antiferromagnetic and ferromagnetic spin chains, Cu${}_2$(OH)${}_3$NO${}_3$, introduce non-trivial magnetic ground states and exotic excitations arising from them. We investigated the magnetic structure of Cu${}_2$(OH)${}_3$NO${}_3$ by ${}^1$H- and ${}^2$H-NMR measurements on single crystals. The internal fields in the ordered state were microscopically measured using the H nuclear moments as a local probe. The directions of the ordered moments were determined by comparing the experimental results to model calculations. The obtained magnetic structure suggests the importance of Dzyaloshinskii-Moriya interactions in stabilizing the low-field magnetic structure. The present result advances the theoretical understanding of the low-field magnetic states and will enable exploration of the exotic magnetic states emerging in high magnetic fields.