The multiferroic RMn 2 O 5 family, where R is rare-earth ion or Y, exhibits rich physics of multiferroicity which has not yet well understood, noting that multiferroicity is receiving attentions for promising application potentials. DyMn 2 O 5 is a representative member of this family. The ferroelectric polarization in DyMn 2 O 5 is claimed to have two anti-parallel components: one (P DM ) from the symmetric exchange striction between the Dy 3+ -Mn 4+ interactions and the other (P MM ) from the symmetric exchange striction between the Mn 3+ -Mn 4+ interactions. We investigate the evolutions of the two components upon a partial substitution of Mn 3+ by nonmagnetic Al 3+ in order to tailor the Mn-Mn interactions and then to modulate component P MM in DyMn 2-x/2 Al x/2 O 5 . It is revealed that the ferroelectric polarization can be successfully reversed by the Al-substitution via substantially suppressing the Mn 3+ -Mn 4+ interactions and thus the P MM . The Dy 3+ -Mn 4+ interactions and the polarization component P DM can sustain against the substitution until a level as high as x=0.2. In addition, the independent Dy spin ordering is shifted remarkably down to an extremely low temperature due to the Al 3+ substitution. The present work not only confirms the existence of the two anti-parallel polarization components but also unveils the possibility of tailoring them independently.

We investigate the effects of slight Dy/Mn off-stoichiometry on the multiferroic behaviors of DyMnO3 (Dy1−xMn1+xO3). It is revealed that the distorted lattice structure and ferroelectric property exhibit higher stability against the Mn deficiency than the Dy deficiency. Since the electric polarization includes the contributions from the Mn-Mn and Dy-Mn interactions, the measured polarization exhibits different dependence on the Mn deficiency from that on the Dy deficiency. The present work suggests that the Dy/Mn off-stoichiometry is detrimental to the ferroelectricity, owing to the modulated spin interactions and reshuffled spin frustration.

Ferrimagnetic spinel compounds AB2X4 (A and B are the magnetic transition elements) are considered to be promising candidates for multiferroics with large magnetization and polarization. In this work, we synthesize polycrystalline spinel MnCr2S4 and characterize the magnetic and ferroelectric properties. Two well-defined ferroelectric phase transitions are demonstrated. The first one occurs at the Cr3+ ferromagnetic phase transition temperature of TC = 65 K, and the other takes place at the Yafet–Kittel (YK) magnetic phase transition temperature of TYK ≈ 5 K. It is suggested that ferroelectricity in the YK phase is driven by the noncollinear triangular YK spin orders and can be greatly tuned by an external magnetic field. Between TYK and TC ranges, another opposite electric polarization sublattice appears, which is enhanced by the external magnetic field just near TC, revealing that this opposite electric polarization is likely related to magnetostriction and the magnetic field can enhance the lattice distortions near TC. Thus, this work paves the way for exploiting ferrimagnetic multiferroicity although more studies are needed to clarify the ferroelectricity mechanism in the Cr3+ ferromagnetic phase.