Jacek C. Wojdeł, Jorge Íñiguez
We show that inducing structural softness in regular magnetoelectric (ME) multiferroics -- i.e., tuning the materials to make their structure strongly reactive to applied fields -- makes it possible to obtain very large ME effects. We present illustrative first-principles results for BiFeO3 thin films.
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We present a thorough density functional theory study of the magneto-electric (ME) effect in Cr$_{2}$O$_{3}$. The spin-lattice ME tensor $α$ was determined in the low-field and spin flop (SF) phases, using the method of dynamical magnetic charges, and found to be the sum of three distinct components. Two of them, a large relativistic "cycloidal" term and a small longitudinal term, are independent on the spin orientation. The third, only active in the SF phases is also of relativistic origin and arises from magnetic-field-induced chirality, leading to a non-toroidal ME response.
We demonstrate that magnetic vortices in which spins are coupled to polar lattice distortions via superexchange exhibit an unusually large linear magnetoelectric response. We show that the periodic arrays of vortices formed by frustrated spins on Kagomé lattices provide a realization of this concept; our {\it ab initio} calculations for such a model structure yield a magnetoelectric coefficient that is 30 times larger than that of prototypical single phase magnetoelectrics. Finally, we identify the design rules required to obtain such a response in a practical material.
Microscopic theory of temperature-dependent magnetoelectric effect in Cr2O3
本研究结合对称性分析、从头算与Monte Carlo模拟，从第一性原理揭示Cr2O3磁电响应的温度依赖性源于非相对论交换作用和自旋涨落，并与实验定量吻合。
Motivated by the discovery of multiferroicity in the geometrically frustrated triangular antiferromagnet CuCrO$_2$ below its Néel temperature $T_N$, we investigate its magnetic and ferroelectric properties using ab initio calculations and Monte Carlo simulations. Exchange interactions up to the third nearest neighbors in the $ab$ plane, inter-layer interaction and single ion anisotropy constants in CuCrO$_2$ are estimated by series of density functional theory calculations. In particular, our results evidence a hard axis along the [110] direction due to the lattice distortion that takes place …
Near room temperature magnetoelectric response and tunable magnetic anisotropy in the two-dimensional magnet 1T-CrTe2
利用ab initio密度泛函理论，研究证实二维1T-CrTe2的磁晶各向异性、居里温度等性质可通过应变或电场调控，为自旋电子学器件应用提供了近室温磁电响应基础。
Large dynamical magnetic effective charges and anti-magnetoelectricity from spin and orbital origin in multiferroic BiCoO$_3$
本文通过第一性原理计算揭示多铁性BiCoO$_3$在线性水平具有反磁电性，其子晶格磁电响应相互抵消，但铁磁相可产生约1000 ps/m的巨大磁电响应。
Strain-tuned magnetoelectric properties of monolayer NiX$_2$ (X = I, Br): a first-principles analysis
本研究基于第一性原理，揭示了通过双轴和单轴应变调控NiX$_2$单层磁电响应的双重机制，阐明了第三近邻自旋对在增强电极化中的关键作用，为二维应变电子器件设计提供了新思路。
Extrinsic multiferroic hybrid structures consisting of ferromagnetic and ferroelectric layers elastically coupled to each other are promising due to their robust magnetoelectric effects even at room temperature. For a quantitative analysis of these magnetoelectric effects, a detailed knowledge of the piezoelectric and magnetoelastic behavior of both constituents as well as their mutual elastic coupling is mandatory. We here report on a theoretical and experimental study of the magnetic behavior of BaTiO3-based extrinsic multiferroic structures. An excellent agreement between molecular dynamics…
Within the broad class of multiferroics (compounds showing a coexistence of magnetism and ferroelectricity), we focus on the subclass of "improper electronic ferroelectrics", i.e. correlated materials where electronic degrees of freedom (such as spin, charge or orbital) drive ferroelectricity. In particular, in spin-induced ferroelectrics, there is not only a {\em coexistence} of the two intriguing magnetic and dipolar orders; rather, there is such an intimate link that one drives the other, suggesting a giant magnetoelectric coupling. Via first-principles approaches based on density functiona…
CoCr$_2$O$_4$ has attracted significant attention recently due to several interesting properties such as magnetostriction, magnetoelectricity etc.. More recent experiments on Fe substituted CoCr$_2$O$_4$ observed a variety of novel phenomena such as the magnetic compensation accompanied by the occurrence of exchange bias, which reverses its sign. Understanding of such phenomena may lead to control the properties of these material in an efficient way to enhance its potential for multifunctional applications. In this paper, we study the microscopic understanding of Fe doping in modifying the str…
There is great interest in hybrid organic-inorganic materials such as metal-organic frameworks (MOFs). The compounds [C(NH$_{2}$)$_{3}$]M(HCOO)$_{3}$, where M=Cu$^{2+}$ or Cr$^{2+}$ are Jahn-Teller (JT) active ions, are MOF with perovskite topology which crystallizes in polar space group Pna2$_{1}$. In inorganic compounds, octahedral tilting and Jahn-Teller structural distortions are usually non-polar distortions. However, in this MOF cooperative interactions between the antiferro-distortive distortions of the framework and the C(NH2)$_{3}$ organic cation via hydrogen bonding breaks the invers…
We present an ab initio study of the BFCO solid solution formed by multiferroics BiFeO3 (BFO) and BiCoO3 (BCO). We find that BFCO presents a strongly discontinuous morphotropic transition between BFO-like and BCO-like ferroelectric phases. Further, for all compositions such phases remain (meta)stable and retain well-differentiated properties. Our results thus suggest that an electric field can be used to switch between these structures, and show that such a switching involves large phase-change effects of various types, including piezoelectric, electric, and magnetoelectric ones.
We study the coexistence of strain- and charge-mediated magnetoelectric coupling in a cobalt (0-7 nm) wedge on ferroelectric [Pb(Mg$_{1/3}$/Nb$_{2/3}$)O$_{3}$]$_{0.68}$-[PbTiO$_{3}$]$_{0.32}$ (011) using surface-sensitive x-ray magnetic circular dichroism spectroscopy at the Co L$_{3,2}$ edges. Three distinct electric field driven remanent magnetization states can be set in the Co film at room temperature. Ab-initio density functional theory calculations unravel the relative contributions of both strain and charge to the observed magnetic anisotropy changes illustrating magnetoelectro-elastic …
Trilinear coupling and toroidicity in multiferroics
本文在朗道理论框架下研究多铁材料中极化、磁化和环极化三个序参量间的三线性耦合，并通过从头计算验证了其在多铁金属Bi$_5$Mn$_5$O$_{17}$中的效应。
Moiré-driven multiferroic order in twisted CrCl$_3$, CrBr$_3$ and CrI$_3$ bilayers
本文通过自旋模型与从头计算揭示扭曲三卤化铬双层中由莫尔图案驱动的多铁序，发现CrBr$_3$双层多铁序最强，并展示强磁电耦合可电控磁斯格明子。
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