we report the importance of interplay of 4f−3d magnetic interactions in inducing ferroelectricity in the centrosymmetric (Pnma) green phase compound Gd2BaCuO5. With decreasing temperature, a long-range incommensurate ordering of both Gd3+ and Cu2+ spins at TN = 11.8K occurs with the modulation vector k = (0,0,g) and a lock-in transition to a strongly noncollinear structure with kc =(0,0,½) at Tloc ∼6K. Both spin structures induce electric polarization consistent with the polar magnetic space groups Pm1′(α,0,g) s s and Paca21, respectively. Based on the symmetry analysis of magnetoelectric interactions, we suggest that the ferroelectricity in both commensurate and incommensurate phases is driven by a complex interplay of two-spins and single-spin contributions from magnetic ions located in noncentrosymmetric environments.
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