We have constructed dichromatic matrices of property coefficients for all 1601 Aizu species. This involves 122 non-magnetic Aizu species and extends the work to the 773 species of phase transitions from disordered magnetic prototypic (parent) phases and the 616 species from ordered magnetic prototypic phases. In addition to coefficients describing the non-magnetic effects we have included the coefficients of pyromagnetic, magnetoelectric, piezomagnetic effects, and magnetic susceptibility. All components of these property tensors are displayed in 13 by 13 matrices; non-zero components of the prototypic phase are given in black and the spontaneous coefficients, that are non-zero in the ferroic phase and zero in the prototypic phase, are given in red.
BiFeO$_3$ is the most famous multiferroic material, but it has no strong spontaneous magnetization due to its antiferromagnetism. Here we show that giant ferroelectric polarization and strong spontaneous magnetization can be both realized in double perovskite Bi$_2$FeMoO$_6$ with R3 (\#146) space group based on BiFeO$_3$. Our first-principles phonon spectra establishes that this multiferroic R3 phase is stable. Our systematic calculations show that it is a spin-polarized semiconductor with gap reaching to 0.54 eV and has a strong ferroelectric polarization of 85$μ$C/cm$^2$. This ferroelctricit…
We have observed the magnetoelectric response at room temperature and above in high-resistive ceramics made of multiferroic Pb(Fe1/2Nb1/2)O3 (PFN) and PFN-based solid solution 0.91PFN-0.09PbTiO3 (PFN-PT). The value of the paramagnetoelectric (PME) coefficient shows a pronounced maximum near the ferroelectric-to-paraelectric phase transition temperature, T_C, and then decreases sharply to zero for T>T_C. The maximal PME coefficient in PFN is about 4x10(-18) s/A. The theoretical description of the PME effect, within the framework of a Landau theory of phase transitions allowing for realistic tem…
Magnetic field-induced spontaneous polarization reversal in multiferroic Mn$_{0.85}$Co$_{0.15}$WO$_4$
本文研究了多铁性系统Mn $_{1-x}$ Co $_x$ WO $_4$（x= 0.135，0.15和0.17）在磁场$H_c$沿单斜$c$轴取向下的磁性和铁电性质。Mn $_{0.85}$ Co $_{0.15}$ WO $_4$处于两个螺旋自旋结构之间的相界，当在$H_c>$ 25 kOe的场中冷却时，表现出铁电极化的自发符号变化。铁电极化的起源进行了研究，并确定了两个磁交换相互作用的极化。在Mn $_{0.85}$ Co $_{0.15}$ WO $_4$域的特征螺旋自旋结构，已知为x $<$ 0.15和x $>$ 0.15，共存并形成域边界。不同的域的全球极化的贡献被确定。Mn $_{0.85}$ Co $_{0.15}$ WO $_4$中的极化反转可以通过对极化的各种贡献和不同螺旋自旋级的磁畴之间的强相关性的组合来解释，从而导致跨畴壁的平滑过渡，这保留了自旋螺旋的手性。
Apart from being so far the only known binary multiferroic compound, CuO has a much higher transition temperature into the multiferroic state, 230 K, than any other known material in which the electric polarization is induced by spontaneous magnetic order, typically lower than 100 K. Although the magnetically induced ferroelectricity of CuO is firmly established, no magnetoelectric effect has been observed so far as direct crosstalk between bulk magnetization and electric polarization counterparts. Here we demonstrate that high magnetic fields of about 50 T are able to suppress the helical mod…
Two-dimensional (2D) magnetoelectric multiferroics are promising multifunctional materials for miniaturized logic and memory devices. Herein, we explore the effectiveness of strain-engineering for tuning the properties of a recently predicted 2D antiferromagnetic-ferroelectric, VOCl2 monolayer. Interestingly, we find that magnetic-ordering and electric polarization can be tuned independently using uniaxial tensile strain along different in-plane lattice vectors. A 4% tensile strain along lattice vector b induces a transition from an antiferromagnetic (AFM) ground state with an out-of-plane mag…
Altermagnetic type-II Multiferroics with Néel-order-locked Electric Polarization
National Laboratory of Solid State Microstructures, School of Physics, Nanjing University（南京大学固体微结构物理学院）；Jiangsu Key Laboratory of Artificial Functional Materials and Department of Materials Science and Engineering,Nanjing University（南京大学材料科学与工程系）；Collaborative Innovation Center of Advanced Microstructures, Nanjing University（南京大学先进微结构协同创新中心）；Center for Quantum Transport and Thermal Energy Science, School of Physics and Technology, Nanjing Normal University（南京师范大学物理科学与技术学院）
Tuning the lattice degree of freedom in nanoscale functional crystals is critical to exploit the emerging functionalities such as piezoelectricity, shape-memory effect, or piezomagnetism, which are attributed to the intrinsic lattice-polar or lattice-spin coupling. Here it is reported that a mechanical probe can be a dynamic tool to switch the ferroic orders at the nanoscale multiferroic phase boundaries in BiFeO 3 with a phase mixture, where the material can be reversibly transformed between the "soft" tetragonal-like and the "hard" rhombohedrallike structures. The microscopic origin of the n…
Over the years attempts have been made to compensate for the inherent weaknesses in the bulk state of the multiferroic BiFeO3, such as high leakage current and the absence of ferromagnetic correlation, and exploit its magnetoelectric potential by forming solid solutions with other perovskites. Studies in the recent few years have shown that alloying of BiFeO3 with BaTiO3, both with and without additives, can induce both ferroelectric and ferromagnetic switching. While the coexistence of both the ferroic orders is encouraging from the view point of technological applications, the origin of ferr…
Synthesis and extensive structural, pyroelectric, magnetic, dielectric and magneto-electric characterizations are reported for polycrystalline Co4Nb2O9 towards unraveling the multiferroic state especially in reference to the magnetic spin flop transition. Magnetic measurements confirm the Co4Nb2O9 becomes antiferromagnetic (AFM) at around 28 K but no clear evidence for spin-flop effect was found. Associated with the magnetic phase transition, a sharp peak in pyroelectric current indicates the appearance of the strong magneto-electric coupling below Neel temperature (TN) with a large coupling c…
Complex oxides with tunable structures have many fascinating properties, though high-quality complex oxide epitaxy with precisely controlled composition is still out of reach. Here we have successfully developed solution-based single crystalline epitaxy for multiferroic (1-x)BiTi(1-y)/2FeyMg(1-y)/2O3-(x)CaTiO3 (BTFM-CTO) solid solution in large area, confirming its ferroelectricity at atomic-scale with a spontaneous polarization of 79~89uC/cm2. Careful compositional tuning leads to a bulk magnetization of ~0.07uB/Fe at room temperature, enabling magnetically induced polarization switching exhi…
We study the structural, ferroelectric, and magnetic properties of the potentially multiferroic Aurivillius phase material Bi$_5$FeTi$_3$O$_{15}$ using first principles electronic structure calculations. Calculations are performed both with PBE and PBEsol exchange correlation functionals. We conclude that PBE systematically overestimates the lattice constants and the magnitude of the ferroelectric distortion, whereas PBEsol leads to good agreement with available experimental data. We then assess a potential site preference of the Fe$^{3+}$ cation by comparing 10 different distributions of the …
Based on variable components global optimization algorithm, we predict a stable two-dimensional (2D) phase of boron phosphide with 1:5 stoichiometry, i.e. boron pentaphosphide (BP_5) monolayer, which has a lower formation energy than that of the commonly believed graphitic phase (g-BP). BP_5 monolayer is a multiferroic material with coupled ferroelasticity and ferroelectricity. The predicted reversible strain is up to 41.41%, which is the largest among all reported ferroelastic materials. Due to the non-centrosymmetric structure and electronegativity differences between boron and phosphorus at…
In the last few years, some ideas of electric manipulations in ferromagnetic heterostructures have been proposed for developing next generation spintronic devices. Among them, the magnetization switching driven by spin-orbit torque (SOT) is being intensely pursued. Especially, how to control the switching current density, which is expected to enrich device functionalities, has aroused much interest among researchers all over the world. In this paper, a novel method to adjust the switching current is proposed, and the BiFeO3 (BFO) based heterostructures with opposite spontaneous polarizations f…
At ambient pressure (P) and below 5.5 K, olivine-type Mn2GeO4 hosts a multiferroic (MF) phase where a multicomponent, i.e., multi-k magnetic order generates spontaneous ferromagnetism and ferroelectricity (FE) along the c axis. Under high P the FE disappears above 6 GPa, yet the P evolution of the magnetic structure remained unclear based on available data. Here we report high P single crystal neutron diffraction experiments in theMF phase at T = 4.5 K.We observe clearly that the incommensurate spiral component of the magnetic order responsible for FE varies little with P up to 5.1 GPa. With s…
Multiferroic materials, in which ferroelectric and magnetic ordering coexist, are of fundamental interest for the development of novel memory devices that allow for electrical writing and non-destructive magnetic readout operation. The great challenge is to create room temperature multiferroic materials with strongly coupled ferroelectric and ferromagnetic (or ferrimagnetic) orderings. BiFeO3 has been the most heavily investigated single-phase multiferroic to date due to the coexistence of its magnetic order and ferroelectric order at room temperature. However, there is no net magnetic moment …
Anisotropic multiferroic properties of SrMnGe2O6 pyroxene single crystals were systematically investigated by means of magnetization, heat capacity, pyroelectric current measurement and elastic and inelastic neutron scattering experiments. Single crystal neutron diffraction allows us to unambiguously reveal the presence of two incommensurate magnetic orderings: a non-polar amplitude-modulated collinear sinusoidal magnetic structure emerges at TN1=4.36(2)K followed by a polar elliptical cycloidal spin structure below TN2=4.05(2)K. Pyroelectric current measurements on single crystal confirm the …
Observation of different spin behavior with temperature variation and Cr substitution in a multiferroic compound YMn$_2$O$_5$
本文通过对YMn $_{2-x}$ Cr $_x$ O $_5$（x= 0.0，0.05）系列的低场体磁测量，探讨了自旋的集体响应。YMn $_2$ O $_5$的低场交流磁化率和直流磁化强度与电学测量中所观察到的类似，表现出多重跃迁。使用各种时间相关的磁化协议，已经观察到，在公度和非公度相位的自旋的行为是截然不同的。YMn $_{1.95}$ Cr $_{0.05}$ O $_5$与经历反铁磁有序的母体相比经历亚铁磁有序，具有增强的磁有序温度。由于母体化合物是一种重要的多铁性材料，在原子结构没有任何重大变化的情况下出现自发磁化是相当重要的。此外，在Cr取代化合物中观察到磁记忆效应，而在母体化合物中不存在。
Novel imaging spin-filter techniques, which are based on low energy electron diffraction, are currently of high scientific interest. To improve the spin-detection efficiency a variety of new materials have been introduced in recent years. A new class of promising spin-filter materials are represented by multiferroic systems, as both magnetic and electric ordering exist in these materials. We have investigated Fe/BaTiO3(001), which defines a prominent candidate due to its moderate spontaneous polarization, for spin filter applications calculating diffraction patterns for spin polarized electron…
Multiferroics (MFs) are materials with two or more ferroic orders, like spontaneous ferroelectric and ferromagnetic polarizations. Such materials can exhibit a magnetoelectric effect whereby magnetic and ferroelectric polarizations couple linearly, reminiscent of, but not identical to the electromagnetic $\boldsymbol{E}\cdot \boldsymbol{B}$ axion coupling. Here we point out a possible mechanism in which an external dark matter axion field couples linearly to ferroic orders in these materials without external applied fields. We find the magnetic response to be linear in the axion-electron coupl…
Non-resonant and Resonant X-ray Scattering Studies on Multiferroic TbMn2O5
全面的X射线散射研究，包括共振散射在锰的L-边缘，Tb的L-和M-边缘，进行了单晶TbMn 2 O 5。在铁电相的布拉格禁戒位置观察到X射线强度，除了晶格和磁调制峰。它们的强度随温度的变化关系以及调制波矢之间的关系为交换伸缩引起的铁电性提供了直接的证据。共振X射线散射的结果表明，存在多个磁序，表现出不同的温度依赖性。在24 K附近的超导体到无公度的相变归因于自旋阻挫几何中磁序的相位滑移引起的位错。我们提出低温无公度相由反相畴壁分隔的公度磁畴组成，反相畴壁在相变时突然降低自发极化。
Magnetoelectric Coupling in Nickel-Cobalt Ferrite and Lanthanum Ferrite Heterostructure Composites: Experimental Evidence and Simulation-Driven Insights
The rare-earth chromates (RECrO$_3$) and manganites (REMnO$_3$) where, RE = Eu, Y, Dy, Ho, Gd are constantly under scrutiny in search of room temperature magnetoelectric multiferroics. However, the artefacts and undesirable signal in some of the measurements pose a severe challenge in confirming the ferroelectric (FE) phase, especially in reference to pyroelectric current measurement technique. In this regard, we propose a simple modified approach to pyroelectric current measurement named as 4-segment thermal cycling protocol. This protocol assists in isolating the elusive, irreversible therma…
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 app…
Bismuth ferrite (BiFeO3) is one of the most promising multiferroics with a sufficiently high ferroelectric (FE) and antiferromagnetic transition temperatures, and magnetoelectric (ME) coupling coefficient at room temperature, and thus it is highly sensitive to the impact of cross-influence of applied electric and magnetic fields. According to the urgent demands of nanotechnology miniaturization for ultra-high density data storage in advanced nonvolatile memory cells, it is very important to reduce the sizes of multiferroic nanoparticles in the self-assembled arrays without serious deterioratio…
Ab-initio spin-polarized Density Functional Theory plus U is used to study the electronic and magnetic properties of tetragonal doped barium titanate (Ba$_{1-x}$Eu$_x$O$_3$) system for different europium (Eu$^{3+}$) concentrations. For this study, the Projector Augmented Wave (PAW) method and a Perdew-Zunger (LSDA) approximation, which has been used for the exchange correlation energy, have been considered taking into account a supercell model. In this model, the spin polarization as well as the Hubbard's potential have been used for the correction of the electron-electron Coulomb interactions…
Multiferroic materials have attracted much interest due to the unusual coexistence of ferroelectric and (anti-)ferromagnetic ground states in a single compound. They offer an exciting platform for new physics and potentially novel devices. BiFeO$_3$ is one of the most celebrated of multiferroic materials with highly desirable properties. It is the only known room-temperature multiferroic with $T_\mathrm{C}\approx 1100~ \mathrm{K}$ and $T_\mathrm{N}\approx 650~\mathrm{K}$, and exhibits one of the largest spontaneous electric polarisation, $P\approx 80~μ\mathrm{C/cm}^2$. At the same time, it has…
The anisotropic optical properties of multiferroic BiFeO$_3$ thin films have been determined with Mueller matrix ellipsometry at room-temperature. The full dielectric tensors of tetragonal-like and rhombohedral-like BiFeO$_3$ phases epitaxially grown on LaAlO$_3$ and SrTiO$_3$ single crystal substrates, respectively, within the spectral range of 0.6 and 6.5 eV are reported. Strain-driven anisotropy changes and transition shifts are observed as well as evidence of sub-band gap many-particle excitations are found. The transition shifts, mostly to higher energies for the highly strained tetragona…
We report on polarized infrared reflectivity measurements of multiferroic, monoclinic MnWO4 between 10K and 295K. The full dielectric tensor and the frequency dependence of the orientation of the principal axes have been determined in the frequency range of the phonons. All infrared-active phonon modes (7 A_u modes and 8 B_u modes) are unambiguously identified. In particular the strongest B_u modes have been overlooked in previous studies, in which the monoclinic symmetry was neglected in the analysis. Using a generalized Drude-Lorentz model, we determine the temperature dependence of the phon…
Multiferroic materials attract considerable interest because of the wide range of potential applications such as spintronic devices, data storage and sensors. As a strong candidate for the applications among the limited list of single-phase multiferroic materials, BiFeO3 (BFO) is a quite attractive material due to its multiferroic properties at room temperature (RT). However, BFO is widely known to have large leakage current and small spontaneous polarization due to the existence of crystalline defects such as oxygen vacancies. Furthermore, the magnetic moment of pure BFO is very weak owing to…
Magnetic and electric properties in the distorted tetrahedral spin chain system Cu3Mo2O9
研究了扭曲四面体准一维自旋体系Cu $_3$ Mo $_2$ O $_9$的多铁性，其中低维效应和磁阻挫效应同时出现.通过测量介电常数和自发电极化的强度，阐明了在$T_{\rm N}=7.9$ K温度下零磁场下反铁磁有序与铁电性质共同形成，并得到了磁场-温度相图。发现当磁场$H$平行于a轴时，反铁磁相具有平行于c轴的电极化的强度.另一方面，在平行于c轴的反铁磁相中，$H$有三个不同的铁电相。
