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DyMnO hosts the less addressed duality of multiferroicity, owing to the Dy-Mn exchange striction and inverse Dzyaloshinskii-Moriya interaction between Mn spin pairs. Although the duality in DyMnO has been discussed earlier, there remains a question whether the Mn magnetic sublattice is necessarily multiferroic for generating the Dy-Mn exchange striction. In this work, we investigate the multiferroicity of Dy(MnFe)O (0 ≤ x ≤ 0.1) through detailed magnetic and ferroelectric characterization. It is found that Fe-doping continuously suppresses the independent Dy spin order but instead promotes the Dy-Mn(Fe) coupling. This coupling benefits the Dy-Mn(Fe) exchange striction which remarkably enhances the ferroelectric polarization at a low doping level (x ≤ 0.015), beyond which the Mn spiral spin order breaks down leading to collapse of the macroscopic polarization at x ≥ 0.05. This work discloses the crucial role of Mn spiral spin order in stabilizing the Dy-Mn exchange striction and thus highlights the duality of multiferroicity in DyMnO.

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Mg:Fe:Cu:LiNbO3 crystals with different [Li]/[Nb] ratios (0.946, 1.05, 1.20, 1.38) were prepared by the Czochralski method. The crystal structure and the occupancy of impurity ions were analyzed by X-ray diffraction (XRD). The effective segregation coefficient was analyzed by an inductively coupled plasma-atomic emission spectrometer (ICP-AES). The optical uniformity of the crystal is analyzed by birefringence gradient. The results show that the dopant ions do not change the crystal structure, and the concentration of dopant ions changes with the ratio of [Li]/[Nb]. The greater the ratio of [Li]/[Nb], the better the optical uniformity. Finally,we conclude that when the [Li]/[Nb] ratio approaches 1.20, the intrinsic defects of Mg:Fe:Cu:LiNbO3 crystals almost disappear and the crystals approach the stoichiometric ratio. When the [Li]/[Nb] ratio is 1.38, the optical uniformity of the crystal is the best.