Dzyaloshinskii-Moriya interaction and the magnetic ground state in magnetoelectric LiCoPO${}_4$

Magnetic structures are investigated by means of neutron diffraction to shine a light on the intricate details that are believed to be key to understanding the magnetoelectric effect in LiCoPO${}_4$ . At zero field, a spontaneous spin canting of $\phi =7(1{)}^{\circ }$ is found. The spins tilt away from the easy $b$-axis toward $c$. Symmetry considerations lead to the magnetic point group $m_z^{\mathrm{\prime }}$, which is consistent with the previously observed magnetoelectric tensor form and weak ferromagnetic moment along $b$. For magnetic fields applied along $a$, the induced ferromagnetic moment couples via the Dzyaloshinskii-Moriya interaction to yield an additional field-induced spin canting. An upper limit to the size of the interaction is estimated from the canting angle.