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Register a new userExperimental observation of ferrielectricity in multiferroic DyMn2O5: revisiting the electric polarization
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The electric polarization and its magnetic origins in multiferroic RMn2O5, where R is rare-earth ion, are still issues under debate. In this work, the temperature-dependent electric polarization of DyMn2O5, the most attractive member of this RMn2O5 family, is investigated using the pyroelectric current method upon varying endpoint temperature of the electric cooling, plus the positive-up-negative-down (PUND) technique. It is revealed that DyMn2O5 at low temperature does exhibit the unusual ferrielectricity rather than ferroelectricity, characterized by two interactive and anti-parallel ferroelectric sublattices which show different temperature-dependences. The two ferroelectric sublattices are believed to be generated from the symmetric exchange-striction mechanisms associated with the Mn-Mn spin interactions and Dy-Mn spin interactions, respectively. The path-dependent electric polarization reflects the first-order magnetic transitions in the low temperature regime. The magnetoelectric effect is mainly attributed to the Dy spin order which is sensitive to magnetic field. The present experiments may be helpful for clarifying the puzzling issues on the multiferroicity in DyMn2O5 and probably other RMn2O5 multiferroics.
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The study of abrupt increases in magnetization with magnetic field known as metamagnetic transitions has opened a rich vein of new physics in itinerant electron systems, including the discovery of quantum critical end points with a marked propensity to develop new kinds of order. However, the electric analogue of the metamagnetic critical end point, a metaelectric critical end point has not yet been realized. Multiferroic materials wherein magnetism and ferroelectricity are cross-coupled are ideal candidates for the exploration of this novel possibility using magnetic-field (emph{H}) as a tuning parameter. Herein, we report the discovery of a magnetic-field-induced metaelectric transition in multiferroic BiMn$_{2}$O$_{5}$ in which the electric polarization (emph{P}) switches polarity along with a concomitant Mn spin-flop transition at a critical magnetic field emph{H}$_{rm c}$. The simultaneous metaelectric and spin-flop transitions become sharper upon cooling, but remain a continuous crossover even down to 0.5 K. Near the emph{P}=0 line realized at $mu_{0}$emph{H}$_{rm c}$$approx$18 T below 20 K, the dielectric constant ($varepsilon$) increases significantly over wide field- and temperature (emph{T})-ranges. Furthermore, a characteristic power-law behavior is found in the emph{P}(emph{H}) and $varepsilon$(emph{H}) curves at emph{T}=0.66 K. These findings indicate that a magnetic-field-induced metaelectric critical end point is realized in BiMn$_2$O$_5$ near zero temperature.
We investigate the electronic structure and the ferroelectric properties of the recently discovered multiferroic ScFeO$_3$ by means of ab-initio calculations. The $3d$ manifold of Fe in the half-filled configuration naturally favors an antiferromagnetic ordering, with a theoretical estimate of the antiferromagnetic Neel temperature in good agreement with the experimental values. We find that the inversion symmetry-breaking is driven by the off-centering of Sc atoms, which results in a large ferroelectric polarization of $sim$105,$mu$C/cm$^{2}$. Surprisingly the ferroelectric polarization is sensitive to the local magnetization of the Fe atoms resulting in a large negative magnetoelectric interaction. This behavior is unexpected in type-I multiferroic materials because the magnetic and ferroelectric orders are of different origins.
We report electric polarization and magnetization measurements in single crystals of double perovskite Lu2MnCoO6 using pulsed magnetic fields and optical second harmonic generation (SHG) in DC magnetic fields. we observe well-resolved magnetic field-induced changes in the electric polarization in single crystals and thereby resolve the question about whether multiferroic behavior is intrinsic to these materials or an extrinsic feature of polycrystals. We find electric polarization along the crystalline b-axis, that is suppressed by applying a magnetic fields along c-axis and advance a model for the origin of magnetoelectric coupling. We furthermore map the phase diagram using both capacitance and electric polarization to identify regions of ordering and regions of magnetoelectric hysteresis. This compound is a rare example of coupled hysteretic behavior in the magnetic and electric properties. The ferromagnetic-like magnetic hysteresis loop that couples to hysteretic polarization can be attributed not to ordinary ferromagnetic domains, but to the rich physics of magnetic frustration of Ising-like spins in the axial next-nearest neighbor interaction model.
The multiferroic RMn2O5 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. DyMn2O5 is a representative member of this family. The ferroelectric polarization in DyMn2O5 is claimed to have two anti-parallel components: one (PDM) from the symmetric exchange striction between the Dy3+-Mn4+ interactions and the other (PMM) from the symmetric exchange striction between the Mn3+-Mn4+ interactions. We investigate the evolutions of the two components upon a partial substitution of Mn3+ by nonmagnetic Al3+ in order to tailor the Mn-Mn interactions and then to modulate component PMM in DyMn2-x/2Alx/2O5. It is revealed that the ferroelectric polarization can be successfully reversed by the Al-substitution via substantially suppressing the Mn3+-Mn4+ interactions and thus the PMM. The Dy3+-Mn4+ interactions and the polarization component PDM 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 Al3+ 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.
Our results describe an unprecedented example of change in the mechanism of magnetically-induced electric polarization from spin current to spin-dependent p-d hybridization model. We have followed the evolution of the magnetic structures of (ND4)2[FeCl5 D2O] compound using single crystal neutron diffraction under external magnetic field. The spin arrangements change from incommensurate cycloidal to commensurate distorted-cycloidal and finally to quasi-collinear. The determination of the magnetic structures allows us to explain the observed electric polarization in the different ferroelectric phases. Two different magneto-electric coupling mechanisms are at play: the spin-current mechanism for external magnetic field below 5 T, and the spin dependent p-d hybridization mechanism for magnetic field above this value, being this compound the first example reported presenting this sequence of magneto-electric coupling mechanisms.
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