Magnetoelectricity in the system RAl3 (BO3)4 (R = Tb, Ho, Er, Tm)

The magnetoelectric effect in the system RAl3(BO3)4 (R = Tb, Ho, Er, Tm) is investigated between 3 K and room temperature and at magnetic fields up to 70 kOe. We show a systematic increase of the magnetoelectric effect with decreasing magnetic anisotropy of the rare earth moment. A giant magnetoelectric polarization is found in the magnetically (nearly) isotropic HoAl3(BO3)4. The polarization value in transverse field geometry at 70 kOe reaches 3600 μC/m2 which is significantly higher than reported values for the field-induced polarization of linear magnetoelectric or even multiferroic compounds. The results indicate a very strong coupling of the f-moments to the lattice. They further indicate the importance of the field-induced ionic displacements in the unit cell resulting in a polar distortion and a change in symmetry on a microscopic scale. The system RAl3(BO3)4 could be interesting for the technological utilization of the high-field magnetoelectric effect.