Magnetoelectric Effect in the Nd3Ga5SiO14 Paramagnet

The electric polarization induced by a magnetic field H in Nd₃Ga₅SiO₁₄ noncentrosymmetric trigonal paramagnetic single crystals has been detected. In low fields, it is quadratic in H and its components in the basal ab plane are described by two magnetoelectric susceptibilities α₁ and α₂. The polarization along the trigonal c axis is manifested only starting from the fourth-order terms ~H⁴. In high magnetic fields at low temperatures, when the magnetic moments of Nd³⁺ are saturated, the polarization qualitatively changes its field dependence to nearly quasilinear for all crystallographic directions and increases strongly (up to 250 μC/m² at 5 T along the c axis). The effects observed in Nd₃Ga₅SiO₁₄ have been quantitatively described using the spin Hamiltonian of the Nd³⁺ ion in local low-symmetric (C₂) sites taking into account the magnetoelectric interaction allowed by symmetry. Magnetoelectric invariants nonlinear in H that make it possible to describe the observed the field, temperature, and angular dependences of the polarization using several magnetoelectric parameters have been constructed in terms of the local susceptibilities of Nd³⁺ ions taking into account the nonequivalence of their magnetization.