X-ray resonant magnetic scattering studies of rare earth magnetic ordering were performed on perovskite manganites RMnO3 (R = Dy, Gd) in an applied magnetic field. The data reveal that the field-induced three-fold polarization enhancement for H || a (H approx. 20 kOe) observed in DyMnO3 below 6.5 K is due to a re-emergence of the Mn-induced Dy spin order with propagation vector k(Dy) = k(Mn) = 0.385 b*, which accompanies the suppression of the independent Dy magnetic ordering, k(Dy) = 1/2 b*. For GdMnO3, the Mn-induced ordering of Gd spins is used to track the Mn-ordering propagation vector. The data confirm the incommensurate ordering reported previously, with k(Mn) varying from 0.245 to 0.16 b* on cooling from T_N(Mn) down to a transition temperature T'. New superstructure reflections which appear below T' suggest a propagation vector k(Mn) = 1/4 b* in zero magnetic field, which may coexist with the previously reported A-type ordering of Mn. The Gd spins order with the same propagation vector below 7 K. Within the ordered state of Gd at T = 1.8 K we find a phase boundary for an applied magnetic field H || b, H = 10 kOe, which coincides with the previously reported transition between the ground state paraelectric and the ferroelectric phase of GdMnO3. Our results suggest that the magnetic ordering of Gd in magnetic field may stabilize a cycloidal ordering of Mn that, in turn, produces ferroelectricity.
Magnetically induced electric polarization reversal in multiferroic TbMn$_2$O$_5$: Terbium spin reorientation studied by resonant x-ray diffraction
在多铁性TbMn $_2$ O $_5$中，铽离子的行为形成磁电耦合的关键部分。结果是在2 T下磁感应电极化的强度反转。在这篇文章中，我们提出了在外加磁场下的铽磁性结构的第一个直接测量。与目前对\tmo磁性的解释相反，我们表明，在电极化的强度反转时，铽子晶格采用倾斜的反铁磁结构，具有平行于\textit{a}轴的磁矩的大分量。此外，我们提供的证据之间的耦合锰的3D磁性结构和铽$4f$磁性，这是在难以捉摸的磁电机制发挥重要的意义。
Giant magnetostriction in insulating magnetic materials is highly required for applications but is rarely observed. Here we show that giant magnetostriction (> 1500 ppm) can be achieved in an insulating transition metal oxide CaBaCo4O7 where the ferrimagnetic ordering at TC ~ 62 K is associated with a huge change in the lattice. Moreover, because this material is pyroelectric with a non-switchable electric polarization (P), the giant magnetostriction results in a record-breaking magnetoelectric effect - a gigantic change of electric polarization (deltaP ~ 1.6 μC/cm2) in response to the applied…
Electric polarization is a geometric phenomenon in solids and has a close relationship to the symmetry of the system. Here we propose a mechanism to dynamically induce and manipulate electric polarization by using an external light field. Specifically, we show that application of bicircular lights (BCLs) control the rotational symmetry of the system and can generate electric polarization. To this end, we use Floquet theory to study a system subjected to a two-frequency drive. We derive an effective Hamiltonian with high frequency expansions, for which the electric polarization is computed with…
We study electric polarization and nonlinear optical effects in spin systems with broken inversion symmetry. We apply strong coupling expansion to the underlying electronic Hamiltonians, and systematically derive expressions for electric polarization in spin systems that are represented in terms of spin operators. The magnon representation of the obtained electric polarization operator allows us to compute linear and nonlinear optical responses by the standard diagrammatic method. We apply our formalism to Heisenberg model with alternating coupling constants and $J_1$-$J_2$ model with inversio…
We consider phase separated states in magnetic oxides (MO) thin films. We show that these states have a non-zero electric polarization. Moreover, the polarization is intimately related to a spatial distribution of magnetization in the film. Polarized states with opposite polarization and opposite magnetic configuration are degenerate. An external electric field removes the degeneracy and allows to switch between the two states. So, one can control electric polarization and magnetic configuration of the phase separated MO thin film with the external electric field.
We investigate electric polarizations emergent perpendicular to an applied thermal gradient in insulating systems. The thermally-induced electric polarization, known as thermopolarization, has been studied conventionally in the case that an electric polarization appears along the thermal gradient. Here, we focus on the antisymmetric component of the thermopolarization tensor and reveal that it becomes nonzero owing to the ferro-type order for electric-toroidal dipole moments. To describe local electric polarizations originating from the disproportionation of localized electronic clouds, we int…
Exceptional magneto-electric coupling and spontaneous electric polarization in anti-ferromagnet Co4Nb2O9
合成和广泛的结构，热释电，磁性，介电和磁电特性的报告多晶Co 4 Nb 2 O 9对解开的多铁性状态，特别是在参考磁自旋翻转过渡。磁性测量证实了Co 4 Nb 2 O 9在28 K左右成为反铁磁（AFM），但没有发现自旋翻转效应的明显证据，与磁相变相关的热释电电流的尖峰表明在低于Neel温度（TN）时出现了强的磁电耦合，其耦合常数高达17.8 uC/m^2 T。利用温度振荡技术，我们确定了Co_4 Nb_2 O_9是一种真正的多铁性材料，在反铁磁态下具有自发的电极化的强度。
Experimental observation of ferrielectricity in multiferroic DyMn2O5: revisiting the electric polarization
多铁性RMn_2 O_5（R为稀土离子）的电极化的强度及其磁起源仍是一个有争议的问题。在这项工作中，依赖于温度的电极化的强度的DyMn 2 O 5，这个RMn 2 O 5家族中最有吸引力的成员，使用热释电电流的方法，在不同的电冷却的终点温度，加上正向上-负向下（PUND）技术进行了研究。结果表明，DyMn_2O_5在低温下表现出铁电性而非铁电性，表现为两个相互作用且反平行的铁电亚晶格，且具有不同的温度依赖性。这两个铁电亚晶格被认为是由Mn-Mn自旋相互作用和Dy-Mn自旋相互作用的对称交换-伸缩机制产生的。路径依赖的电极化的强度反映了低温区的一级磁转变。这种磁电效应主要归因于Dy的自旋序对磁场的敏感性。本实验有助于澄清DyMn_2 O_5和其他RMn_2 O_5多铁性材料中令人困惑的问题。
Surface physics dominated by bulk properties has been one of the central interests in modern condensed matter physics, from electric polarization to bulk-boundary correspondence of topological insulators and superconductors. Here, we extend theory of electric polarization to chirality polarizations, that is, surface charges corresponding to local antisymmetries characterized as a bulk property. Using the notion of chirality polarizations, we prove the recently proposed spectral bulk-boundary correspondence, a generalization of bulk-boundary correspondence in chiral symmetric systems into compl…
In RBaCo4O7 (R = Ca, Y and Rare earth) cobaltite family, only CaBaCo4O7 shows 3D long range ferrimagnetic and spin driven electric polarization properties. In the present study, we have investigated the structural, magnetic and electric polarization properties in YBaCo4O7 and DyBaCo4O7 members of this family and the obtained results are compared with the CaBaCo4O7. The compound YBaCo4O7 showed a series of magnetic transitions in agreement with reported literature, additionally, a cluster glass behavior below 5 K is observed. Powder neutron diffraction studies on DyBaCo4O7 cobaltite showed an o…
We develop a nonperturbative approach to the bulk polarization of crystalline electric insulators in $d\geq1$ dimensions. Formally, we define polarization via the response to background fluxes of both charge and lattice translation symmetries. In this approach, the bulk polarization is related to properties of magnetic monopoles under translation symmetries. Specifically, in $2d$ the monopole is a source of $2π$-flux, and the polarization is determined by the crystal momentum of the $2π$-flux. In $3d$ the polarization is determined by the projective representation of translation symmetries on …
High-harmonic generation (HHG), a typical nonlinear optical effect, has been actively studied in electron systems such as semiconductors and superconductors. As a natural extension, we theoretically study HHG from electric polarization, spin current and magnetization in magnetic insulators under terahertz (THz) or gigahertz (GHz) electromagnetic waves. We use simple one-dimensional spin chain models with or without multiferroic coupling between spins and the electric polarization, and study the dynamics of the spin chain coupled to an external ac electric or magnetic field. We map spin chains …
