Interplay of 4f-3d magnetism and ferroelectricity in DyFeO 3

DyFeO 3 exhibits a weak ferromagnetism ( T N Fe ∼ 645 K) that disappears below a spin-reorientation (Morin) transition at T SR Fe ∼ 50 K. It is also known that applied magnetic field induces ferroelectricity at the magnetic ordering temperature of Dy ions ( T N Dy ∼ 4.5 K). Here, we show that the ferroelectricity exists in the weak ferromagnetic state ( T SR Fe < T < T N,C ) without applying a magnetic field, indicating the crucial role of weak ferromagnetism in inducing ferroelectricity. 57 Fe Mössbauer studies show that a hyperfine field ( B hf ) deviates from the mean-field–like behaviour that is observed in the weak ferromagnetic state and decreases below the onset of the spin-reorientation transition (80 K), implying that the B hf above T SR had an additional contribution from Dy ions due to the induced magnetization by the weak ferromagnetic moment of the Fe sublattice and below T SR this contribution decreases due to collinear ordering of the Fe sublattice. These results clearly demonstrate the presence of magnetic interactions between Dy(4 f ) and Fe(3 d ) and their correlation with ferroelectricity in the weak ferromagnetic state of DyFeO 3 .