Magnetoelectric and Magnetoelastic Properties of Easy-Plane Ferroborates with A Small Ionic Radius

The magnetic, magnetoelectric, and magnetoelastic properties of RFe3(BO3)4 ferroborates are studied. The measurement of the field dependences of the magnetoelectric polarization along the a axis in holmium ferroborate and in the mixed composition Ho0.5Sm0.5Fe3(BO3)4 revealed the following dependences for easy-plane ferroborates: (a) the longitudinal and transverse magnetoelectric effects have the opposite signs and (b) magnetically induced polarization changes its sign in a field close to the field of exchange between rare-earth and iron ions. These dependences agree well with theoretical predictions based on the symmetry of the compounds. The relatively low f-d exchange field in holmium ferroborate (about 20 kOe), which magnetizes the rare-earth subsystem, causes smaller polarization jumps (about 30 μC/m2) in fields lower than 10 kOe as compared to the jumps in other easy-plane ferroborates (R = Sm, Nd). The increase in the electric polarization induced in HoFe3(BO3)4 in magnetic fields higher than 100 kOe (200–300 μC/m2) is found to be significantly smaller than in neodymium ferroborate, which indicates a substantial dependence of the magnetoelectric effects on the electronic structure of a rare-earth ion.