Magnetization, magnetoelectric polarization, and specific heat of HoGa3(BO3)4

A comprehensive experimental and theoretical study of magnetic, magnetoelectric, thermal, and spectroscopic characteristics of HoGa3(BO3)4 gallium borate single crystals has been performed. A large magnetoelectric effect exceeding its values found in all iron and aluminum borates except HoAl3(BO3)4 has been observed. The magnetoelectric polarization of HoGa3(BO3)4 equals ΔP ba (B a ) ≈ −1020 μC/m2 at T = 5 K in a magnetic field of 9 T. The theoretical treatment based on the crystal field model for rare-earth ions provides a unified approach for the consistent interpretation of all measured characteristics. The crystal-field parameters are determined. The temperature (in the 3–300 K range) and magnetic field (up to 9 T) dependences of the magnetization, the Schottky anomaly in the temperature dependence of the specific heat, and its shift in the field B ‖ c are described. To compare the thermal properties of HoGa3(BO3)4 with those of HoAl3(BO3)4 exhibiting record values of the polarization, the specific heat of HoAl3(BO3)4 at various B values and the temperature dependence of the polarization ΔP b (T) in the applied magnetic field of 9 T have been measured.