Magnetoelectric and magnetoelastic properties of easy-plane ferroborates with a small ionic radius

The magnetic, magnetoelectric, and magnetoelastic properties of RFe 3 (BO 3 ) 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 Ho 0.5 Sm 0.5 Fe 3 (BO 3 ) 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/m 2 ) 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 HoFe 3 (BO 3 ) 4 in magnetic fields higher than 100 kOe (200–300 μC/m 2 ) 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.