A giant magnetoelectric polarization is found in HoAl${}_3$(BO${}_3$)${}_4$. The polarization in transverse field geometry at 70 kOe reaches 3600 $\mu \hspace{0.5em}\mathrm{C}/{\mathrm{m}}^2$, which is significantly higher than reported values of linear magnetoelectric or even multiferroic compounds. The magnetostrictive effect is also measured and compared with the magnetoelectricity. The results show that spin-lattice coupling in HoAl${}_3$(BO${}_3$)${}_4$ is extremely strong and that the magnetic field causes a large polar distortion of the ionic positions in the unit cell.

• Received 9 May 2011

DOI:https://doi.org/10.1103/PhysRevB.83.180417