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Dennis Meier - One of the best experts on this subject based on the ideXlab platform.
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Domain Walls - Improper Ferroelectric Domain Walls
Domain Walls, 2020Co-Authors: Donald M. Evans, Andres Cano, Ch. Cochard, R. G. P. Mcquaid, J. M. Gregg, Dennis MeierAbstract:This chapter focuses on the specific physical properties at Domain Walls in ferroelectric materials where the spontaneous electric polarization appears as a by-product of a structural or magnetic phase transition, and not as its primary order parameter. The chapter begins with a short introduction to the fundamentals of improper ferroelectricity, followed by a discussion of emergent functional Domain wall properties in different improper ferroelectric model systems. It then covers the broad variety of electronic states and application opportunities associated with improper ferroelectric Domain Walls in hexagonal manganites. Next, this chapter addresses the electronic transport and manipulation of Domain Walls in boracites, and presents additional magnetoelectric coupling phenomena that arise when the interaction of magnetic spins and electric charges gives rise to improper ferroelectricity. A perspective regarding future research and application opportunities of improper ferroelectric Domain Walls is given last.
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Domains and Domain Walls in multiferroics
Physical Sciences Reviews, 2020Co-Authors: Donald Evans, Dennis Meier, Vincent Garcia, M. BibesAbstract:Multiferroics are materials combining several ferroic orders such as ferroelectricity, ferro-(or anti-ferro-) magnetism, ferroelasticity and ferrotoroidicity [1]. They are of interest both from a fundamental perspective , as they have multiple (coupled) non-linear functional responses-providing a veritable myriad of correlated phenomena, and because of the opportunity to apply these functionalities for new device applications. One application is, for instance, in no-volatile memory, which has led to special attention being devoted to ferroelectric and magnetic multiferroics. For this application, the vision is to combine the low writing power of ferroelectric information with the easy, non-volatile, reading of magnetic information to give a 'best of both worlds' computer memory: however, for this to be realised the two ferroic orders need to be intimately linked via the magnetoelec-tric effect. The magnetoelectric coupling-the way polarization and magnetization reverse-is manifested by the formation and interactions of Domains and Domain Walls, and so to understand how to engineer future devices one must first understand the interactions of Domains and Domain Walls. In this article, we provide a short introduction to the Domain formation in ferroelectrics and ferromagnets, as well as different microscopy techniques that enable the visualization of such Domains. We then review the recent research on multiferroic Domains and Domain Walls, including their manipulation and intriguing properties, such as enhanced conductivity and anomalous magnetic order. Finally, we discuss future perspectives concerning the field of multiferroic Domain Walls and emergent topological structures such as ferroelectric vortices and skyrmions. 1 Domain structures in (multi-)ferroics 1.1 Introduction to ferroic Domains and Domain Walls Ferroic materials are defined by the appearance of an order parameter (e.g., elastic, electric or magnetic) at a non-disruptive phase transition. This order parameter can point in at least two symmetrically equivalent directions (polarities) between which it can be switched by the application of an external field. When cooling through the phase transition in zero-field, the polarities have the same energy and, as a consequence, both polarities appear inside the ferroic material. These regions are called Domains and the interfaces that separate them are call Domain Walls. While this shows, trivially, that multiple Domains form naturally in ferroics, the details of how many Domains, their size, and where they form, depend on several energy terms, as well as the local defect structure. In the following, we will give a brief outline of how ferroic Domains and Domain Walls form, using a ferroelectric as an illustrative example; although, as we will see, analogous arguments can be made for the formation of Domains and Domains Walls in ferromagnets. For a more complete and in-depth descriptions of the physics of ferroelectric and ferromagnetic Domains we refer to, for instance, the textbooks by Tagantsev et al. [2] and by Hubert & Schäfer [3]. A proper ferroelectric is a material for which the spontaneous electric polarization plays the role of the primary symmetry breaking order parameter, which can completely describe the phase transition into the ferroic state [4],[5]. Practically, this means energy contributions related to this order parameter are very important in the system, particularly for the Domain formation. For instance, in ferroelectrics, surfaces perpendicular to the ferroelectric polarization comprise bound charges that create a strong depolarizing field (Fig. 1a): this is a major driving force for Domain formation. The depolar-izing field can be minimized by either (i) screening the surface charges of the ferroelectric with surface adsorbates or metallic electrodes (Fig. 1b), or (ii) the formation of ferroelectric Domains, for example, 180° Domains, so that the net polarization at the surface averages to zero (Fig. 1c). The number and size of the ferroelectric Domains that form will
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Observation of uncompensated bound charges at improper ferroelectric Domain Walls
Nano Letters, 2019Co-Authors: Peggy Schoenherr, Jakob Schaab, Andres Cano, Mario Hentschel, Konstantin Shapovalov, Manfred Fiebig, Edith Bourret, Massimiliano Stengel, Dennis MeierAbstract:Low-temperature electrostatic force microscopy (EFM) is used to probe unconventional Domain Walls in the improper ferroelectric semiconductor Er0.99Ca0.01MnO3 down to cryogenic temperatures. The low-temperature EFM maps reveal pronounced electric far fields generated by partially uncompensated Domain-wall bound charges. Positively and negatively charged Walls display qualitatively different fields as a function of temperature, which we explain based on different screening mechanisms and the corresponding relaxation time of the mobile carriers. Our results demonstrate Domain Walls in improper ferroelectrics as a unique example of natural interfaces that are stable against the emergence of electrically uncompensated bound charges. The outstanding robustness of improper ferroelectric Domain Walls in conjunction with their electronic versatility brings us an important step closer to the development of durable and ultrasmall electronic components for next-generation nanotechnology.
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topological Domain Walls in helimagnets
Nature Physics, 2018Co-Authors: Peggy Schoenherr, Yoshinori Tokura, Jan Muller, L Kohler, Achim Rosch, Naoya Kanazawa, Markus Garst, Dennis MeierAbstract:Domain Walls naturally arise whenever a symmetry is spontaneously broken. They interconnect regions with different realizations of the broken symmetry, promoting structure formation from cosmological length scales to the atomic level1,2. In ferroelectric and ferromagnetic materials, Domain Walls with unique functionalities emerge, holding great promise for nanoelectronics and spintronics applications3–5. These Walls are usually of Ising, Bloch or Neel type and separate homogeneously ordered Domains. Here we demonstrate that a wide variety of new Domain Walls occurs in the presence of spatially modulated Domain states. Using magnetic force microscopy and micromagnetic simulations, we show three fundamental classes of Domain Walls to arise in the near-room-temperature helimagnet iron germanium. In contrast to conventional ferroics, the Domain Walls exhibit a well-defined inner structure, which—analogous to cholesteric liquid crystals—consists of topological disclination and dislocation defects. Similar to the magnetic skyrmions that form in the same material6,7, the Domain Walls can carry a finite topological charge, permitting an efficient coupling to spin currents and contributions to a topological Hall effect. Our study establishes a new family of magnetic nano-objects with non-trivial topology, opening the door to innovative device concepts based on helimagnetic Domain Walls. The observation of three new classes of Domain wall demonstrates the importance of topological disclination and dislocation defects in the helimagnet iron germanium, via analogy with grain boundaries in cholesteric liquid crystals.
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topological Domain Walls in helimagnets
arXiv: Strongly Correlated Electrons, 2017Co-Authors: Peggy Schoenherr, Yoshinori Tokura, Jan Muller, L Kohler, Achim Rosch, Naoya Kanazawa, Markus Garst, Dennis MeierAbstract:A magnetic helix arises in chiral magnets with a wavelength set by the spin-orbit coupling. We show that the helimagnetic order is a nanoscale analog to liquid crystals, exhibiting topological structures and Domain Walls that are distinctly different from classical magnets. Using magnetic force microscopy and micromagnetic simulations, we demonstrate that - similar to cholesteric liquid crystals - three fundamental types of Domain Walls are realized in the helimagnet FeGe. We reveal the micromagnetic wall structure and show that they can carry a finite skyrmion charge, permitting coupling to spin currents and contributions to a topological Hall effect. Our study establishes a new class of magnetic nano-objects with non-trivial topology, opening the door to innovative device concepts based on helimagnetic Domain Walls.
Helmut Schultheiss - One of the best experts on this subject based on the ideXlab platform.
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magnetic Domain Walls as reconfigurable spin wave nanochannels
Nature Nanotechnology, 2016Co-Authors: Kai Wagner, Attila Kakay, Katrin Schultheiss, A Henschke, T Sebastian, Helmut SchultheissAbstract:Magnetic Domain Walls in a permalloy sample can be arranged to define waveguides for the transmission of information via magnons.
Jan Seidel - One of the best experts on this subject based on the ideXlab platform.
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Domain Walls - Electronics Based on Domain Walls
Domain Walls, 2020Co-Authors: Jan Seidel, Ramamoorthy RameshAbstract:This chapter reviews some of the initial developments and recently introduced potential application concepts related to Domain Walls in ferroelectrics and multiferroics. It gives a special (non-exclusive) focus on the heavily investigated bismuth ferrite BiFeO3 system as one of the rare examples of a single phase room-temperature multiferroic system that can be widely tailored in application relevant epitaxial thin films. Here, DWs as well as other topological structures reveal new ways to novel tailored states of matter with a wide range of electronic properties. Domain wall electronics, particularly with ferroelectrics and multiferroics, provides new nanotechnological concepts for identifying, understanding, and designing new material properties. However, this chapter observes that there has been very little work done on controlling electronic correlations.
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efficient photovoltaic current generation at ferroelectric Domain Walls
Physical Review Letters, 2011Co-Authors: Jan Seidel, S Y Yang, Esther Alarconllado, R Ramesh, J W AgerAbstract:We elucidate the mechanism of a newly observed photovoltaic effect which occurs in ferroelectrics with periodic Domain structures. Under sufficiently strong illumination, Domain Walls function as nanoscale generators of the photovoltaic current. The steps in the electrostatic potential function to accumulate electrons and holes on opposite sides of the Walls while locally reducing the concentration of the oppositely charged carriers. As a result, the recombination rate adjacent to the Walls is reduced, leading to a net diffusion current. In open circuit, photovoltages for periodically ordered Domain Walls are additive and voltages much larger than the band gap can be generated. The internal quantum efficiency for individual Domain Walls can be surprisingly high, approaching 10% for above band-gap photons. Although we have found the effect in BiFeO(3) films, it should occur in any system with a similar periodic potential.
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conduction at Domain Walls in oxide multiferroics
Nature Materials, 2009Co-Authors: Lane W Martin, Yinghao Chu, Jan Seidel, Q Zhan, A Rother, M E HawkridgeAbstract:Domain Walls may play an important role in future electronic devices, given their small size as well as the fact that their location can be controlled. Here, we report the observation of room-temperature electronic conductivity at ferroelectric Domain Walls in the insulating multiferroic BiFeO3. The origin and nature of the observed conductivity are probed using a combination of conductive atomic force microscopy, high-resolution transmission electron microscopy and first-principles density functional computations. Our analyses indicate that the conductivity correlates with structurally driven changes in both the electrostatic potential and the local electronic structure, which shows a decrease in the bandgap at the Domain wall. Additionally, we demonstrate the potential for device applications of such conducting nanoscale features. Domain Walls may be important in future electronic devices, given their small size as well as the fact that their location can be controlled. In the case of insulating multiferroic oxides, Domain Walls are now discovered to be electrically conductive, suggesting their possible use in logic and memory applications.
Andres Cano - One of the best experts on this subject based on the ideXlab platform.
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Domain Walls - Improper Ferroelectric Domain Walls
Domain Walls, 2020Co-Authors: Donald M. Evans, Andres Cano, Ch. Cochard, R. G. P. Mcquaid, J. M. Gregg, Dennis MeierAbstract:This chapter focuses on the specific physical properties at Domain Walls in ferroelectric materials where the spontaneous electric polarization appears as a by-product of a structural or magnetic phase transition, and not as its primary order parameter. The chapter begins with a short introduction to the fundamentals of improper ferroelectricity, followed by a discussion of emergent functional Domain wall properties in different improper ferroelectric model systems. It then covers the broad variety of electronic states and application opportunities associated with improper ferroelectric Domain Walls in hexagonal manganites. Next, this chapter addresses the electronic transport and manipulation of Domain Walls in boracites, and presents additional magnetoelectric coupling phenomena that arise when the interaction of magnetic spins and electric charges gives rise to improper ferroelectricity. A perspective regarding future research and application opportunities of improper ferroelectric Domain Walls is given last.
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Observation of uncompensated bound charges at improper ferroelectric Domain Walls
Nano Letters, 2019Co-Authors: Peggy Schoenherr, Jakob Schaab, Andres Cano, Mario Hentschel, Konstantin Shapovalov, Manfred Fiebig, Edith Bourret, Massimiliano Stengel, Dennis MeierAbstract:Low-temperature electrostatic force microscopy (EFM) is used to probe unconventional Domain Walls in the improper ferroelectric semiconductor Er0.99Ca0.01MnO3 down to cryogenic temperatures. The low-temperature EFM maps reveal pronounced electric far fields generated by partially uncompensated Domain-wall bound charges. Positively and negatively charged Walls display qualitatively different fields as a function of temperature, which we explain based on different screening mechanisms and the corresponding relaxation time of the mobile carriers. Our results demonstrate Domain Walls in improper ferroelectrics as a unique example of natural interfaces that are stable against the emergence of electrically uncompensated bound charges. The outstanding robustness of improper ferroelectric Domain Walls in conjunction with their electronic versatility brings us an important step closer to the development of durable and ultrasmall electronic components for next-generation nanotechnology.
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Polarization control at spin-driven ferroelectric Domain Walls.
Nature Communications, 2015Co-Authors: Naëmi Leo, Andres Cano, Manfred Fiebig, Anders Bergman, Narayan Poudel, Bernd Lorenz, Dennis MeierAbstract:Unusual electronic states arise at ferroelectric Domain Walls due to the local symmetry reduction, strain gradients and electrostatics. This particularly applies to improper ferroelectrics, where the polarization is induced by a structural or magnetic order parameter. Because of the subordinate nature of the polarization, the rigid mechanical and electrostatic boundary conditions that constrain Domain Walls in proper ferroics are lifted. Here we show that spin-driven ferroelectricity promotes the emergence of charged Domain Walls. This provides new degrees of flexibility for controlling Domain-wall charges in a deterministic and reversible process. We create and position a Domain wall by an electric field in Mn0.95Co0.05WO4. With a magnetic field we then rotate the polarization and convert neutral into charged Domain Walls, while its magnetic properties peg the wall to its location. Using atomistic Landau-Lifshitz-Gilbert simulations we quantify the polarization changes across the two wall types and highlight their general occurrence.
Mirjam Cvetič - One of the best experts on this subject based on the ideXlab platform.
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Effective Supergravity for Supergravity Domain Walls
Physics Letters B, 2002Co-Authors: Mirjam Cvetič, Neil LambertAbstract:We discuss the low energy effective action for the Bosonic and Fermionic zero-modes of a smooth BPS Randall-Sundrum Domain wall, including the induced supergravity on the wall. The result is a pure supergravity in one lower dimension. In particular, and in contrast to non-gravitational Domain Walls or Domain Walls in a compact space, the zero-modes representing transverse fluctuations of Domain wall have vanishing action.
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supergravity Domain Walls
Physics Reports, 1997Co-Authors: Mirjam Cvetič, Harald H. SolengAbstract:Abstract We review the status of Domain Walls in N = 1 supergravity theories for the vacuum Domain Walls as well as dilatonic Domain Walls. We concentrate on a systematic analysis of the nature of the space-time in these Domain wall backgrounds and the special role that supersymmetry is playing in determining the nature of such configurations. Isotropic vacuum Domain Walls that can exist between isolated minima of an N = l supergravity matter potential fall into three classes: 1. (i) extreme Walls, which are static planar Walls between supersymmetric minima, 2. (ii) non-extreme Walls, which are expanding bubbles with two centres and 3. (iii) ultra-extreme Walls, which are bubbles of false vacuum decay. Dilatonic Walls arise in N = 1 supergravity with a general coupling of the linear supermultiplet. The dilaton field, a scalar component of the linear multiplet, has no perturbative self-interaction, but couples to the matter potential responsible for the formation of the wall. The dilaton drastically changes the global space-time properties of the wall. For the extreme ones the spacetime structure depends on the strength of the dilaton coupling, while for non- and ultra-extreme solutions one always encounters naked singularities (in the absence of non-perturbative corrections to the dilaton potential). Non-perturbative effects may modify the dilaton coupling so that it has a discrete non-compact symmetry ( S -duality). In this case the non and ultra-extreme solutions can reduce to the singularity-free vacuum Domain wall solutions. We also summarize Domain wall configurations within the effective theory of N = 1 superstring vacua, with and without inclusion of non-perturbative string effects, and also provide a comparison with other topological defects of perturbative string vacua.
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Supergravity Domain Walls
Physics Reports, 1997Co-Authors: Mirjam Cvetič, Harald H. SolengAbstract:We review the status of Domain Walls in $N=1$ supergravity theories for both the vacuum Domain Walls as well as dilatonic Domain Walls. We concentrate on a systematic analysis of the nature of the space-time in such Domain wall backgrounds and the special role that supersymmetry is playing in determining the nature of such configurations.