钙钛矿型氧化物非常规铁电研究进展

钙钛矿型氧化物因具有丰富的磁性、铁电、力学和光学等诸多功能属性,在电子信息通信材料器件领域中有广阔的应用前景.在各种物理性质之中,铁电极化因其产生机制多样,并能与磁性和晶格应变相互耦合形成多铁性等特点,近十多年来一直被作为凝聚态物理研究的国际热点问题.与以自发极化作为初级序参量的常规铁电材料不同,非常规铁电材料中的铁电极化是被其他的序参量诱导而产生的.本综述围绕无机钙钛矿型氧化物非常规铁电体的研究进展进行了总结.回顾了该体系经典唯象理论和原子尺度的微观模型,有序排列的人工钙钛矿超晶格型结构,以及稀土正铁氧体单晶的反铁磁畴壁结构中非常规铁电的极化强度大小及其诱导机制,为系统理解非常规铁电提供了理论途径.     

Room-temperature vertical ferroelectricity in rhenium diselenide induced by interlayer sliding

One variety of ferroelectricity that results from lateral relative movements between the adjacent atomic layers is referred to as sliding ferroelectricity, which generates an interfacial charge transfer and hence a polarization reversal. The mechanism of sliding ferroelectricity existent in van der Waals crystals is quite distinct from the conventional ferroelectric switching mechanisms mediated by ion displacement. It creates new possibilities for the design of two-dimensional (2D) ferroelectrics since it can be achieved even in non-polar systems. Before 2D ferroelectrics can be widely employed for practical implementations, however, there is still significant work to be done on several fronts, such as exploring ferroelectricity possibly in more potential 2D systems. Here, we report the experimental observation of room-temperature robust vertical ferroelectricity in layered semiconducting rhenium diselenide (ReSe₂), a representative member of the transition metal dichalcogenides material family, based on a combined research of nanoscale piezoresponse and second harmonic generation measurements. While no such ferroelectric behavior was seen in 1L ReSe₂, 2L ReSe₂ exhibits vertical ferroelectricity at ambient environment. Based on density-functional theory calculations, we deduce that the microscopic origin of ferroelectricity for ReSe₂ is uncompensated vertical charge transfer that is dependent on in-plane translation and switchable upon interlayer sliding. Our findings have important ramifications for the ongoing development of sliding ferroelectricity since the semiconducting properties and low switching barrier of ReSe₂ open up the fascinating potential for functional nanoelectronics applications.     

General theory for the ferroelectric polarization induced by spin-spiral order

The ferroelectric polarization of triangular-lattice antiferromagnets induced by helical spin-spiral order is not explained by any existing model of magnetic-order-driven ferroelectricity. We resolve this problem by developing a general theory for the ferroelectric polarization induced by spin-spiral order and then by evaluating the coefficients needed to specify the general theory on the basis of density functional calculations. Our theory correctly describes the ferroelectricity of triangular-lattice antiferromagnets driven by helical spin-spiral order and incorporates known models of magnetic-order-driven ferroelectricity as special cases.     

4d-5p orbital mixing and asymmetric In 4d-O 2p hybridization in InMnO3: a new bonding mechanism for hexagonal ferroelectricity

Recent studies on the ferroelectricity origin of YMnO(3), a prototype of hexagonal manganites (h-RMnO(3), where R is a rare-earth-metal element), reveal that the d(0)-ness of a Y(3+) ion with an anisotropic Y 4d-O 2p hybridization is the main driving force of ferroelectricity. InMnO(3) (IMO) also belongs to the h-RMnO(3) family. However, the d(0)-ness-driven ferroelectricity cannot be expected because the trivalent In ion is characterized by a fully filled 4d orbital. Here we propose a new bonding mechanism of the hexagonal ferroelectricity in IMO: intra-atomic 4d(z(2))-5p(z) orbital mixing of In followed by asymmetric 4d(z(2))(In)-2p(z)(O) covalent bonding along the c axis.     

铁电极化子动力学理论

在铁电屏蔽理论的基础上发展铁电极化子动力学理论,用来解释铁电体的极化反转现象.理论结果与TGS单晶的实验结果符合得很好.由该理论还可进一步用来研究铁电发射的基本物理过程 关键词： 铁电极化子 极化反转 慢极化效应     

Coupling of magnetic and ferroelectric hysteresis by a multicomponent magnetic structure in Mn2GeO4

The olivine compound Mn(2)GeO(4) is shown to feature both a ferroelectric polarization and a ferromagnetic magnetization that are directly coupled and point along the same direction. We show that a spin spiral generates ferroelectricity, and a canted commensurate order leads to weak ferromagnetism. Symmetry suggests that the direct coupling between the ferromagnetism and ferroelectricity is mediated by Dzyaloshinskii-Moriya interactions that exist only in the ferroelectric phase, controlling both the sense of the spiral rotation and the canting of the commensurate structure. Our study demonstrates how multicomponent magnetic structures found in magnetically frustrated materials like Mn(2)GeO(4) provide a new route towards functional materials that exhibit coupled ferromagnetism and ferroelectricity.     

Multiferroic properties in terbium orthoferrite

Multiferroic properties in a polycrystalline terbium orthoferrite are investigated. Different thermomagnetic behaviors are observed in different magnetic fields, which is attributed to the suppression of the low temperature magnetic phase by an external magnetic field. Further studies reveal that the ferroelectricity originates from the spin configuration below3.5 K. In addition, the magnetic field control of electric polarization and dielectric constant is observed, which suggests a magnetoelectric effect in TbFeO3. The origin of ferroelectricity in this rare-earth orthoferrite is discussed.     

Multiferroicity: the coupling between magnetic and polarization orders

Multiferroics, defined for those multifunctional materials in which two or more kinds of fundamental ferroicities coexist, have become one of the hottest topics of condensed matter physics and materials science in recent years. The coexistence of several order parameters in multiferroics brings out novel physical phenomena and offers possibilities for new device functions. The revival of research activities on multiferroics is evidenced by some novel discoveries and concepts, both experimentally and theoretically. In this review, we outline some of the progressive milestones in this stimulating field, especially for those single-phase multiferroics where magnetism and ferroelectricity coexist. First, we highlight the physical concepts of multiferroicity and the current challenges to integrate the magnetism and ferroelectricity into a single-phase system. Subsequently, we summarize various strategies used to combine the two types of order. Special attention is paid to three novel mechanisms for multiferroicity generation: (1) the ferroelectricity induced by the spin orders such as spiral and E-phase antiferromagnetic spin orders, which break the spatial inversion symmetry; (2) the ferroelectricity originating from the charge-ordered states; and (3) the ferrotoroidic system. Then, we address the elementary excitations such as electromagnons, and the application potentials of multiferroics. Finally, open questions and future research opportunities are proposed.     

Competition between ferroelasticity and ferroelectricity

In the crystals of the KH₂PO₄ family, the properties of ferroelasticity and ferroelectricity strongly interact. It is for example possible to change by application of an electric field the orientation of the phase front between high temperature and low temperature phases, and to observe the rotation of reticular planes during an electric hysteresis cycle drawing. These phenomena, as the existence of a quasi constant domain width illustrate the particular competition between ferroelasticity and ferroelectricity in these compounds.     

柔性Pb(Zr_(0.53)Ti_(0.47))O_3薄膜的高温铁电特性

随着柔性电子产品的迅速发展,具有优异铁电和压电性的Pb(Zr_(0.53)Ti_(0.47))O_3 (PZT)薄膜在柔性的非易失性存储器、传感器和制动器等器件中有广泛的应用前景.同时,由于外部环境越来越复杂,具有高温稳定特性的材料和器件受到越来越多的关注.本文在耐高温的二维层状氟晶云母衬底上,用脉冲激光沉积技术制备出外延的PZT薄膜,并通过机械剥离的方法,得到柔性的外延PZT薄膜.研究了Pt/PZT/SRO异质结的铁电和压电性及其高温特性,发现样品表现出优越的铁电性,剩余极化强度(P_r)高达65μC/cm~2,在弯曲104次后其铁电性基本保持不变,且样品在275℃高温时仍然保持良好的铁电性.本文为柔性PZT薄膜在航空航天器件中的应用提供了实验基础.     

钙钛矿超晶格的演生磁电物性

钙钛矿过渡金属氧化物中存在诸多自由度（如晶格、电荷、自旋和轨道）,这些自由度 之间的相互耦合以及相互竞争会诱导出很多奇异物性,如高温超导、庞磁电阻效应、多铁性等, 这些物性在量子器件的发展过程中扮演了重要的角色。在此基础上,若再将不同特性的氧化物材 料耦合在一起形成超晶格,通过界面处的晶格重组与电子重组,体系可呈现出更加丰富的物理和 更多可调控的性能。本综述主要关注钙钛矿超晶格中的磁电物性。首先介绍了超晶格中磁性调控 的几种物理机制,然后对超晶格中的杂化非本征铁电性以及电子铁电性进行了重点讨论,最后围 绕超晶格中的磁电耦合效应进行了讨论和总结。     

A collection of 505 papers on false or unconfirmed ferroelectric properties in single crystals,ceramics and polymers

This collection presents 505 papers on ferroelectricity in single crystals, ceramics and polymers in which pointed or elliptical hysteresis loops would testify to their ferroelectric properties. In some papers, the authors ensure that ferroelectricity can occur even in materials that do not have a polar axis of symmetry.     

Emergent ferroelectricity in disordered tri-color multilayer structure comprised of ferromagnetic manganites

Multiferroic materials,showing the coexistence and coupling of ferroelectric and magnetic orders,are of great technological and fundamental importance.However,the limitation of single phase multiferroics with robust magnetization and polarization hinders the magnetoelectric effect from being applied practically.Magnetic frustration,which can induce ferroelectricity,gives rise to multiferroic behavior.In this paper,we attempt to construct an artificial magnetically frustrated structure comprised of manganites to induce ferroelectricity.A disordered stacking of manganites is expected to result in frustration at interfaces.We report here that a tri-color multilayer structure comprised of non-ferroelectric La_(0.9)Ca_(0.1)MnO_3(A)/Pr_(0.85)Ca_(0.15)MnO_3(B)/Pr_(0.85)Sr_(0.15)MnO_3(C) layers with the disordered arrangement of ABC-ACBCAB-CBA-BAC-BCA is prepared to form magnetoelectric multiferroics.The multilayer film exhibits evidence of ferroelectricity at room temperature,thus presenting a candidate for multiferroics.     

Hybrid improper ferroelectricity: a mechanism for controllable polarization-magnetization coupling

First-principles calculations are presented for the layered perovskite Ca3Mn2O7. The results reveal a rich set of coupled structural, magnetic, and polar domains in which oxygen octahedron rotations induce ferroelectricity, magnetoelectricity, and weak ferromagnetism. The key point is that the rotation distortion is a combination of two nonpolar modes with different symmetries. We use the term "hybrid" improper ferroelectricity to describe this phenomenon and discuss how control over magnetism is achieved through these functional antiferrodistortive octahedron rotations.     

室温稳定的二维铁电材料：CuInS2P6 及其异质结构

二维铁电材料有助于实现半导体性质与非易失存储特性在微纳尺度上的有机结合,在高集成化电子器件、光电器件、能量收集、及机电耦合系统等领域展现出巨大的应用潜力。二维铁电材料的层状结构,保证了原子层间的可剥离性,为从理论和实验上探索超薄极限下的铁电性质提供理想的研究平台。考虑到二维磁性研究的低温瓶颈,二维铁电材料为实现铁性功能材料的高温器件化与实用化提供了新途径。在本文中,我们介绍了一种室温稳定的二维铁电材料：铜铟硫代磷酸盐(CuInP2S6)。该材料体系的科学内涵和应用前景,引发了新的研究热潮。在本文中,关于其较高的铁电居里转变温度、显著的压电响应、巨大的负纵向压电系数、可调谐的四重势阱铁电特性、以及基于该材料及其异质结构的器件研究,均有所涉及。我们还简要介绍了几种过渡金属硫代磷酸盐化合物材料体系(M^IM^IIIP2(S/Se)6)中的其他代表性材料。最后,我们关于二维铁电材料研究的未来发展方向进行了讨论。     

低维铁电材料研究进展

铁电材料是一类重要的功能材料,铁电元件的小型化、集成化是当今铁电材料发展的一大趋势.但是尺寸效应、表面效应等的存在制约了传统块体铁电材料在纳米尺度下的应用,因而低维度纳米材料中的铁电性能研究成为当前材料科学领域的研究热点之一.本文综述了近年来理论和实验上关于低维铁电材料的探索,包括二维范德瓦耳斯层状铁电材料、共价功能化低维铁电材料、低维钙钛矿材料、外界调控以及二维"铁电金属"等材料的理论预言与实验铁电性的观测;也提出一些物理新机制来解释低维下的铁电性;最后对该领域今后的发展进行了展望.     

Density-functional characterization of the multiferroicity in spin spiral chain cuprates

The ferroelectricity of the spiral magnets LiCu2O2 and LiCuVO4 was examined by calculating the electric polarizations of their spin spiral states on the basis of density-functional theory with spin-orbit coupling. Our work unambiguously reveals that spin-orbit coupling is responsible for the ferroelectricity with the primary contribution from the spin-orbit coupling on the Cu sites, but the asymmetric density distribution responsible for the electric polarization occurs mainly around the O atoms. The electric polarization is calculated to be much greater for the ab-plane than for the bc-plane spin spiral. The observed spin-spiral plane is found to be consistent with the observed direction of the electric polarization for LiCuVO4, but inconsistent for LiCu2O2.     

Computational studies on magnetism and ferroelectricity

Magnetics, ferroelectrics, and multiferroics have attracted great attentions because they are not only extremely important for investigating fundamental physics, but also have important applications in information technology. Here, recent computational studies on magnetism and ferroelectricity are reviewed. We first give a brief introduction to magnets, ferroelectrics, and multiferroics. Then, theoretical models and corresponding computational methods for investigating these materials are presented. In particular, a new method for computing the linear magnetoelectric coupling tensor without applying an external field in the first principle calculations is proposed for the first time. The functionalities of our home-made Property Analysis and Simulation Package for materials (PASP) and its applications in the field of magnetism and ferroelectricity are discussed. Finally, we summarize this review and give a perspective on possible directions of future computational studies on magnetism and ferroelectricity.     

Emergent phenomena in perovskite-type manganites

Perovskite-type manganites exhibit various interesting phenomena arising from complex interplay among spin, charge, orbital, and lattice degrees of freedom. One such example is the keen competition between phases with different spin/charge/orbital orders. Keen competition between antiferromagnetic metal and orbital-ordered insulator is found in the slightly electron-doped regime near Mn⁴⁺ state which is stabilized by the high oxygen-pressure condition. Another one is the emergence of ferroelectricity either induced by the magnetic ordering or independently of the magnetic ordering. As the respective examples, perovskite-type YMnO₃ and Sr_1−xBa_xMnO₃ are discussed. In the YMnO₃, the ferroelectric lattice distortion associated with the E-type spin order is observed for the first time. Displacement-type ferroelectricity with off-center magnetic ions is discovered for Sr_0.5Ba_0.5MnO₃, which shows both large polarization value and strong coupling between ferroelectricity and magnetism.     

An investigation on magnetism, spin–phonon coupling, and?ferroelectricity in multiferroic GdMn2O5

The magnetization, Raman spectroscopy, and ferroelectricity of multiferroic GdMn₂O₅ as a function of temperature and magnetic field are investigated. The complicated magnetic transitions at low temperatures are featured with anomalous Raman mode shifts, dielectric response, and ferroelectricity generation, indicating the significant spin–phonon coupling. It is argued that this coupling is possibly responsible for the electrical polarization generation associated with the incommensurate–commensurate transition.