Micromagnetics has been the method of choice to interpret experimental data in the area of microscopic magnetism for several decades. In this article, we show how progress has been made to extend ...this formalism to include thermal and quantum fluctuations in order to describe recent experimental developments in nanoscale magnetism. For experimental systems with constrained dimensions such as nanodots, atomic chains, nanowires, and thin films, topological defects such as solitons, vortices, skyrmions, and monopoles start to play an increasingly important role, all forming novel types of quasiparticles in patterned low-dimensional magnetic systems. We discuss in detail how soliton-antisoliton pairs of opposite chirality form non-uniform energy barriers against thermal fluctuations in nanowires or pillars. As a consequence of their low barrier energy compared to uniform reversal, they limit the thermal stability of perpendicular recording media. For sufficiently short samples, the non-uniform energy barrier continuously merges into the conventional uniform Néel-Brown barrier. Partial formation of chiral domain walls also determines the magnetic properties of granular nanostructured magnets and exchange spring systems. For a long time, the reconciliation between micromagnetics and quantum mechanics has remained an unresolved challenge. Here it is demonstrated how inclusion of Berry's phase in a micromagnetic action allows for a semiclassical quantization of spin systems, a method that is demonstrated by the simple example of an easy-plane spin. This powerful method allows for a description of quantum dynamics of solitons and breathers which in the latter case agrees with the anisotropic spin-½ XYZ-model. The domain wall or soliton chirality plays an important role as it is coupled to the wavevector of the quasiparticle dispersion. We show how this quantum soliton chirality is detected by polarized neutron scattering in one-dimensional quantum antiferromagnets.
Ferroelectric a1/a2 domain structure has great potentials in high dielectric capacitors and tunable microwave devices. Understanding its structure is crucial to better control the domain ...configurations for future applications. In this paper, PbTiO3 thin films with variant thicknesses are deposited on (110)-oriented GdScO3 substrates by Pulsed Laser Deposition (PLD) and investigated by using conventional transmission electron microscopy (TEM) and Cs-corrected Scanning TEM. Contrast analysis and electron diffractions reveal that PbTiO3 films are domain oriented consisting of a1/a2 and a/c domain structure. The a1/a2 domains are found to distribute periodically and its width increases with increasing film thickness following square root rule. Cs-corrected STEM imaging demonstrates that the domain walls of a1/a2 domain structure have the rotation characteristic of 90° ferroelastic domain wall. The interchange of a1/a2 domains induces the formation of vertex domains composed of two 90° and one 180° domain walls. Strains are mainly concentrated on the domain walls. The formation of this complex domain configuration is discussed in terms of the effect of the misfit strain, film thickness and cooling rate. These results provide novel information about a1/a2 domain structures and are expected to shed some light on modulating a1/a2 ferroelectric domain patterns in the design of ferroelectric-based devices.
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We investigated the synthesis mechanism and giant piezoelectricity of highly 001c textured Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) relaxor based ferroelectric ceramics (texture fraction ...∼94%) with BaTiO3 (BT) templates. The onset of texture occurred at ∼88% relative density (RD), and rapid increase in texture fraction happened with RD>94%. A PbO-rich grain boundary liquid of ∼6–13nm thickness, detected at oriented crystalline interfaces, facilitated epitaxial nucleation and subsequent 001PIN-PMN-PT||001BT growth of textured grains on BT templates. Interfaces between BT templates and PIN-PMN-PT textured grains were found to be coherent and defect-free at the atomic scale, and there was almost no barium diffusion across the interfaces during the texturing process. Nanodomains were clearly visible in the oriented grains. 001c poling ordered the domain structures of textured ceramics and resulted in a more uniform domain size of several hundred nanometers. The textured ternary PIN-PMN-PT ceramics exhibited ∼200% improvement in piezoelectric response relative to their random counterparts, as a result of their piezoelectric anisotropy and engineered domain status along with higher mobility of domain walls.
Magnetoelectric Devices for Spintronics Fusil, S; Garcia, V; Barthélémy, A ...
Annual review of materials research,
07/2014, Letnik:
44, Številka:
1
Journal Article
Recenzirano
The control of magnetism by electric fields is an important goal for the future development of low-power spintronics. Various approaches have been proposed on the basis of either single-phase ...multiferroic materials or hybrid structures in which a ferromagnet is influenced by the electric field applied to an adjacent insulator (usually having a ferroelectric, piezoelectric, or multiferroic character). The electric field effect on magnetism can be driven by purely electronic or electrostatic effects or can occur through strain coupling. Here we review progress in the electrical control of magnetic properties (anisotropy, spin order, ordering temperature, domain structure) and its application to prototype spintronic devices (spin valves, magnetic tunnel junctions). We tentatively identify the main outstanding difficulties and give perspectives for spintronics and other fields.
Spin-based logic architectures provide nonvolatile data retention, near-zero leakage, and scalability, extending the technology roadmap beyond complementary metal-oxide-semiconductor logic
. ...Architectures based on magnetic domain walls take advantage of the fast motion, high density, non-volatility and flexible design of domain walls to process and store information
. Such schemes, however, rely on domain-wall manipulation and clocking using an external magnetic field, which limits their implementation in dense, large-scale chips. Here we demonstrate a method for performing all-electric logic operations and cascading using domain-wall racetracks. We exploit the chiral coupling between neighbouring magnetic domains induced by the interfacial Dzyaloshinskii-Moriya interaction
, which promotes non-collinear spin alignment, to realize a domain-wall inverter, the essential basic building block in all implementations of Boolean logic. We then fabricate reconfigurable NAND and NOR logic gates, and perform operations with current-induced domain-wall motion. Finally, we cascade several NAND gates to build XOR and full adder gates, demonstrating electrical control of magnetic data and device interconnection in logic circuits. Our work provides a viable platform for scalable all-electric magnetic logic, paving the way for memory-in-logic applications.
We describe experimental and theoretical investigations of the magnetic domain formation and the field reversal behavior in antiferromagnetically coupled perpendicular anisotropy multilayers that ...mimic A-type antiferromagnet (AF) structures. The samples are sputter deposited Co/Pt multilayers with perpendicular anisotropy that are periodically interleaved with Ru to mediate an antiferromagnetic interlayer exchange. This structure allows precise tuning of the different magnetic energy terms involved. Using various magnetometry and magnetic imaging techniques as well as resonant soft X-ray scattering we provide a comprehensive study of the remanent and demagnetized configurations as well as the corresponding reversal mechanisms. We find that adding AF exchange to perpendicular anisotropy system alters the typical energy balance that controls magnetic stripe domain formation, thus resulting in two competing reversal modes for the composite system. In the AF-exchange dominated regime the magnetization is ferromagnetically ordered within the film plane with the magnetization of adjacent layers anti-parallel thus minimizing the interlayer AF exchange energy. In the dipolar dominated regime the magnetization pattern forms ferromagnetic (FM) stripe domains where adjacent layers are vertically correlated, but laterally anti-correlated thus minimizing the dipolar energy at the expense of the AF interlayer coupling. By tuning the layer thickness or applying a magnetic field, we observed the co-existence of AF domains and FM stripe domains. We find that a FM phase exists at AF domain boundaries, causing complex mesoscopic domain patterns with surprising reversibility during minor loop field cycling.
Traditional piezoelectric materials cause serious environmental and health issues because of their lead–containing substances, and thus lead–free piezoelectric ceramics would have many applications. ...In this study, we successfully prepared the lead–free ceramics (1-x) (K0·48Na0·48Li0.04) (Nb0·975Sb0.025)O3–x (Bi0·5Na0.5) (Zr0·8Ti0.2)O3 ((1-x)KNLNS–xBNZT, x = 0, 0.005, 0.0075, 0.01, 0.015, 0.02 and 0.03) with rhombohedral–tetragonal (R–T) phase coexistence near room temperature, employing con–entional solid sintering. The minimum cell volume of the ceramics and R–T phase coexistence in them were achieved at a doping amount x = 0.01, which facilitated the optimal performance of the ceramics (d33∼467 pC/N ± 14 pC/N, Tc∼272 °C, εr∼1676, kp∼0.42, where d33: piezoelectric constant; Tc: Curie temperature; εr: dielectric constant; kp: electromechanical coefficient). The ceramics exhibited microstructures with high density and low porosity and had a maximum relative density of 95.68 %. At x = 0.01, the ceramics exhibited a uniformly distributed small domain structures with nanodomains, accounting for their high-voltage electrical properties. Because these stable and reliable piezoelectric (1-x)KNLNS–xBNZT ceramics exhibit excellent electrical performance, they can replace lead–based materials. The direct solid–phase sintering method provides prospects for the large–scale application of the lead–free piezoelectric ceramics.
The 0.99(K0·48Na0·48Li0.04)(Nb0·975Sb0.025)O3–0.01(Bi0·5Na0.5)(Zr0·8Ti0.2)O3 ceramics exhibit excellent piezoelectric properties owing to their nanodomain structures, rhombohedral–tetragonal coexistence phase boundaries at room temperature (25°C ± 5°C) and dense microstructures. Display omitted
Transparent piezoelectrics are highly desirable for numerous hybrid ultrasound-optical devices ranging from photoacoustic imaging transducers to transparent actuators for haptic applications
. ...However, it is challenging to achieve high piezoelectricity and perfect transparency simultaneously because most high-performance piezoelectrics are ferroelectrics that contain high-density light-scattering domain walls. Here, through a combination of phase-field simulations and experiments, we demonstrate a relatively simple method of using an alternating-current electric field to engineer the domain structures of originally opaque rhombohedral Pb(Mg
Nb
)O
-PbTiO
(PMN-PT) crystals to simultaneously generate near-perfect transparency, an ultrahigh piezoelectric coefficient d
(greater than 2,100 picocoulombs per newton), an excellent electromechanical coupling factor k
(about 94 per cent) and a large electro-optical coefficient γ
(approximately 220 picometres per volt), which is far beyond the performance of the commonly used transparent ferroelectric crystal LiNbO
. We find that increasing the domain size leads to a higher d
value for the 001-oriented rhombohedral PMN-PT crystals, challenging the conventional wisdom that decreasing the domain size always results in higher piezoelectricity
. This work presents a paradigm for achieving high transparency and piezoelectricity by ferroelectric domain engineering, and we expect the transparent ferroelectric crystals reported here to provide a route to a wide range of hybrid device applications, such as medical imaging, self-energy-harvesting touch screens and invisible robotic devices.
Summary
In recent years, studies have shed light on the physiological role of plant glutamate receptor‐like channels (GLRs). However, the mechanism by which these channels are activated, and in ...particular, what is the physiological role of their binding to amino acids, remains elusive. The first direct biochemical demonstration that the Arabidopsis thaliana GLR3.3 isoform binds glutamate and other amino acids in a low micromolar range of concentrations was reported only recently. The first crystal structures of the ligand‐binding domains of AtGLR3.3 and AtGLR3.2 isoforms also have been released. We foresee that these new experimental pieces of evidence provide the basis for a better understanding of how GLRs are activated and modulated in different physiological responses.
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