Magnetoelectric susceptibility and magnetic symmetry of magnetoelectrically annealed TbPO4

Measurements are presented of the magnetoelectric (ME) susceptibility tensor $\overleftrightarrow{\alpha }$ of TbP${\mathrm{O}}_4$ crystals which were ME annealed by a method introduced in the present paper and termed "balanced" ME annealing. The form of $\overleftrightarrow{\alpha }$ shows that below the Néel temperature the magnetic symmetry of such crystals is tetragonal (point group $\frac{4^{\prime }}{m^{\prime }{\mathrm{mm}}^{\prime }}$), in contrast to the lower symmetry which describes non-ME-annealed TbP${\mathrm{O}}_4$ crystals. Thus the distortion existing in the latter crystals is suppressed by ME annealing. Also measured are the magnitude (which is larger than in any other known material) and temperature dependence of the single independent component of $\overleftrightarrow{\alpha }$. The improved experimental methods presented include, besides the balanced ME annealing, the simultaneous observation of two components of $\overleftrightarrow{\alpha }$, and a modified procedure for the growth of TbP${\mathrm{O}}_4$ crystals. Magnetoelectric switching, memory, and hysteresis effects are also reported.