Influence of nonmagnetic Ga ions on the magnetoelectric coupling in CuFe1−x Ga x O2

The magnetic properties and dielectric polarization of CuFe1−x Ga x O2 with various nonmagnetic Ga3+ doping levels have been measured in a wide magnetic field region, in which the observed experiment results have been explained by the consequence of the change in exchange interaction, dilution effect, and partial reduction of spin frustration. Compared with pure CuFeO2, doped nonmagnetic Ga3+ ions have an important effect on magnetization and polarization behavior and lead to an enhanced magnetoelectric coupling, especially, an enhanced spontaneous polarization has been observed in the doping amount of 0.02 and 0.05. This magnetoelectric effect appears mainly in the ferroelectric incommensurate magnetic phase region due to the noncollinear magnetic structure with a proper helical order in the CuFeO2. Based on the magnetization and polarization data, a magnetic phase diagram of temperature, magnetic field, and the doping amount are obtained.