Magnetoelectricity and magnetostriction due to the rare-earth moment in TmAl₃ ( BO₃ ) ₄

The magnetic properties, the magnetostriction, and the magnetoelectric effect in the d -electron free rare-earth aluminum borate TmAl₃ ( BO₃ ) ₄ are investigated between room temperature and 2 K. The magnetic susceptibility reveals a strong anisotropy with the hexagonal c axis as the hard magnetic axis. Magnetostriction measurements show a large effect of an in-plane field reducing both the a -axis and c -axis lattice parameters. The magnetoelectric polarization change in a and c directions reaches up to 300 μC/ m2 at 70 kOe with the field applied along the a axis. The magnetoelectric polarization is proportional to the lattice contraction in magnetic field. The results of this investigation prove the existence of a significant coupling between the rare-earth magnetic moment and the lattice in R Al₃ ( BO₃ ) ₄ compounds (R=rare earth). They further show that the rare-earth moment itself will generate a large magnetoelectric effect which makes it easier to study and to understand the origin of the magnetoelectric interaction in this class of materials.