Multiferroic Switching Research Articles

Multiferroicity and giant in-plane negative Poisson\u2019s ratio in wurtzite monolayers

Monolayers of layered materials, such as graphite and molybdenum dichalcogenides, have been the focus of materials science in the last decades. Here, we reveal benign stability and intriguing physical properties in the thinnest monolayer wurtzite (wz) semiconductors, which can be exfoliated from their bulk and stacked to reform the wz crystals. The candidate ZnX and CdX (X = S, Se, Te) monolayers possess low cleavage energy and direct bandgaps, which harbor strongly coupled ferroelectricity and ferroelasticity with low transition barriers, giant in-plane negative Poisson’s ratio, as well as giant Rashba spin splitting, enabling the co-tunability of spin splitting and auxetic magnitudes via multiferroic switching. These wz monolayers can be used as building blocks of devices structures, due to their inherent “self-healable” capacity, which offer more flexibility for semiconductor fabrication and provide a natural platform to probe the interplay of multiple physical effects, bringing light into the rich physics in tetrahedral semiconductors.

Antisymmetry: Fundamentals and Applications

Symmetry is fundamental to understanding our physical world. An antisymmetry operation switches between two different states of a trait, such as two time states, position states, charge states, spin states, or chemical species. This review covers the fundamental concepts of antisymmetry and focuses on four antisymmetries, namely, spatial inversion in point groups, time reversal, distortion reversal, and wedge reversion. The distinction between classical and quantum mechanical descriptions of time reversal is presented. Applications of these antisymmetries—in crystallography, diffraction, determining the form of property tensors, classifying distortion pathways in transition state theory, finding minimum energy pathways, diffusion, magnetic structures and properties, ferroelectric and multiferroic switching, classifying physical properties in arbitrary dimensions, and antisymmetry-protected topological phenomena—are described.

Discovering minimum energy pathways via distortion symmetry groups

Physical systems evolve from one state to another along paths of least energy barrier. Without a priori knowledge of the energy landscape, multidimensional search methods aim to find such minimum energy pathways between the initial and final states of a kinetic process. However in many cases, the user has to repeatedly provide initial guess paths, thus ensuring that the reliability of the final result is heavily user-dependent. Recently, the idea of "distortion symmetry groups" as a complete description of the symmetry of a path has been introduced. Through this, a new framework is enabled that provides a powerful means of classifying the infinite collection of possible pathways into a finite number of symmetry equivalent subsets, and then exploring each of these subsets systematically using rigorous group theoretical methods. The method is shown to lead to the discovery of new, previously hidden pathways for the case studies of bulk ferroelectric switching and domain wall motion in proper and improper ferroelectrics, as well as in multiferroic switching. This approach is applicable to a wide variety of physical phenomena ranging from structural, electronic and magnetic distortions, diffusion, and phase transitions in materials.

Folding catastrophes due to viscosity in multiferroic domains: implications for room-temperature multiferroic switching

Unusual domains with curved walls and failure to satisfy the Landau–Lifshitz-Kittel Law are modeled as folding catastrophes (saddle-node bifurcations). This description of ballistic motion in a viscous medium is based upon early work by Dawber et al 2003 Appl. Phys. Lett. 82 436. It suggests that ferroelectric films can exhibit folds or vortex patterns but not both.

Physics of Oxides for Future Devices

AbstractFerroelectric oxides underwent a renaissance in the 1980s and 1990s, driven by the success in commercializing thin-film ferroelectric random-access memory devices (FRAMs) for applications such as the SONY PlayStation 2 memory board. Materials scientists gravitated into this new field from magnetic oxides and from high-Tcsuperconductivity. But as the FRAM prospects wane and neither dynamic random-access memory devices nor FLASH memory has been replaced, we now require new directions for materials research on oxides. In this article, I outline briefly four new directions for ferroelectric oxide research: something old—ferroelectrically induced ferromagnetism and multiferroic switching; something new—THz emission from oxide ferroelectrics; something borrowed—Heisenberg-like switching of domains in nanoferroelectrics; and something blue—ZnO light-emitting devices. Magnetoelectricity—the linear coupling of polarization and magnetization—was theoretically predicted by Igor Dzyaloshinskii in 1957 and measured experimentally by Astrov two years later. It did not produce commercial devices. Although a flurry of new work occurred in the 1970s, emphasizing boracites—mostly by Hans Schmid in Geneva, no materials were found that exhibited large effects at room temperature. In the past decade, the search has been renewed, emphasizing rare earth systems such as Tb manganites.