Information Storage Devices Research Articles

Magnetic Skyrmion Spectrum Under Voltage Excitation and its Linear Modulation

Magnetic skyrmions are topological quasiparticles with great potential for applications in future information storage and processing devices because of their nanoscale size, high stability, and large velocity. Recently, the high-frequency properties of skyrmions have been explored for magnon nanodevices. Here we systematically study the dynamics of an isolated skyrmion under voltage excitation through the voltage-controlled magnetic anisotropy effect in a circular thin film. A theoretical model considering the demagnetization energy, which has often been neglected or treated superficially in previous skyrmion research but is demonstrated to have importance in determining the skyrmion dynamic state, is developed. With our model, the periodic oscillation of the skyrmion radius can be solved numerically with similar precision compared to micromgnetic simulations, and the characteristic frequency of the skyrmion breathing can be determined analytically with greater precision than previous studies. Furthermore, we find that the breathing skyrmion can be analogized as a modulator by investigating its linear modulation functionality under sinusoidal-form voltage excitation. Different from the conventional modulation system with complex CMOS circuits, this skyrmion modulator device integrates with both the modulation and carrier wave generation functionality, thus showing greater convenience and efficiency in applications. Our findings can provide useful guidance for both theoretical and experimental skyrmions research as well as the development of skyrmion-based magnonic devices with significant potential applicability in future communication system.

Tetragonal Superstructure of the Antiskyrmion Hosting Heusler Compound Mn1.4PtSn.

Skyrmions in non-centrosymmetric magnets are vortex-like spin arrangements, viewed as potential candidates for information storage devices. The crystal structure and noncollinear magnetic structure together with magnetic and spin–orbit interactions define the symmetry of the skyrmion structure. We outline the importance of these parameters in the Heusler compound Mn1.4PtSn which hosts antiskyrmions, a vortex-like spin texture related to skyrmions. We overcome the challenge of growing large micro-twin-free single crystals of Mn1.4PtSn, which has proved to be the bottleneck for realizing bulk skyrmionic/antiskyrmionic states in a compound. The use of 5d-transition metal, platinum, together with manganese as constituents in the Heusler compound such as Mn1.4PtSn is a precondition for the noncollinear magnetic structure. Because of the tetragonal inverse Heusler structure, Mn1.4PtSn exhibits large magneto-crystalline anisotropy and D2d symmetry, which are necessary for antiskyrmions. The superstructure in Mn1.4PtSn is induced by Mn-vacancies, which enable a ferromagnetic exchange interaction to occur. Mn1.4PtSn, the first known tetragonal Heusler superstructure compound, opens up a new research direction for properties related to the superstructure in a family containing thousands of compounds.

Reversibly controlled magnetic domains of Co film via electric field driven oxygen migration at nanoscale

Electric field control of perpendicular magnetic anisotropy (PMA) can enable low power consumption for perpendicular magnetic random access memory devices. However, the tuning of PMA by the electric field in ferromagnetic metal thin films is less efficient and limited to the interface due to the screening effect. Alternatively, the magnetoionic effect can control PMA efficiently, which utilizes ion migrations over the surface of the ferromagnetic metal by interfacing it with the charge reservoir of oxygen ions like GdOx. In this paper, we report the reversibly controlled magnetic domains of PMA Co in the Pt/Co/GdOx trilayer via the electric field at the nanoscale using conductive atomic force microscopy and magnetic force microscopy (MFM). The magnetic domain phase values determined by MFM decrease and increase when negative and positive bias voltages of magnitude 4 V are applied to the surface of GdOx, respectively. These results suggest a path toward control of PMA materials at the nanoscale by the electric field for information storage devices.

Development of Bioelectronic Devices Using Bionanohybrid Materials for Biocomputation System.

Bioelectronic devices have been researched widely because of their potential applications, such as information storage devices, biosensors, diagnosis systems, organism-mimicking processing system cell chips, and neural-mimicking systems. Introducing biomolecules including proteins, DNA, and RNA on silicon-based substrates has shown the powerful potential for granting various functional properties to chips, including specific functional electronic properties. Until now, to extend and improve their properties and performance, organic and inorganic materials such as graphene and gold nanoparticles have been combined with biomolecules. In particular, bionanohybrid materials that are composed of biomolecules and other materials have been researched because they can perform core roles of information storage and signal processing in bioelectronic devices using the unique properties derived from biomolecules. This review discusses bioelectronic devices related to computation systems such as biomemory, biologic gates, and bioprocessors based on bionanohybrid materials with a selective overview of recent research. This review contains a new direction for the development of bioelectronic devices to develop biocomputation systems using biomolecules in the future.

Probing the Magnetic Ordering of Antiferromagnetic MnPS3 by Raman Spectroscopy.

Ferromagnetic/antiferromagnetic materials are of crucial importance in information storage and spintronics devices. Herein we present a comprehensive study of 2D Heisenberg-like antiferromagnetic material MnPS3 by optical contrast and Raman spectroscopy. We propose a criterion of 0.1 × ( N - 1) < (Δ R/ R)max < 0.1 × N ( N ≤ 7) to quickly identify the layer number N by using maximum optical contrast (Δ R/ R)max of few-layer MnPS3 on a SiO2/Si substrate (90 nm thick SiO2). The Raman modes are also identified by polarization Raman spectroscopy. Furthermore, by temperature-dependent Raman measurements, we obtain three phase transition temperatures of MnPS3. The transition temperature at around 80 K corresponds to the transition from the antiferromagnetic to paramagnetic phase; the one at around 120 K is related to its second magnetic phase transition temperature due to two-dimensional spin critical fluctuations; the one at around 55 K is associated with unbinding of spin vortices. Our studies provide more evidence to advance knowledge of the magnetic critical dynamics of 2D ferromagnetic/antiferromagnetic systems.

Magnetism and ferroelectricity in BiFeO3 doped with Ga at Fe sites

Theoretical calculations were performed to investigate the effect of isovalent substitution of Fe with Ga on the magnetic and ferroelectric properties in BiFeO3 doped with 16.6% and 8.3% Ga. Such substitution will break the G-type anti-ferromagnetic order and enhance the magnetism of BiFeO3 by forming a stable ferrimagnetic order. The doped system maintains robust spontaneous polarization that is sufficiently large for practical applications at room temperature. The findings explain experimentally observed magnetism. The coexistence of magnetism and ferroelectricity in the doped BiFeO3 render it a candidate material for application to information storage and spintronics devices.

Synthesis and Characterization of Certain Photoactive Liquid Crystalline Poly(ester amides) from 2,5-Pyridine Dicarboxylic Acid

A new series of four photo-crosslinkable thermotropic liquid crystalline poly(ester amides) were synthesized by direct polycondensation of 2,5-pyridine dicarboxylic acid with two different varying diols and diamines. Two diamines employed in the synthesis were 4,4′-diaminodiphenyl methane and 1,4-diaminobenzene. The arylidene diols 2,5-bis(4-hydroxy-3-methoxybenzylidene)cyclopentanone and 2,6-bis(4-hydroxy-3-methoxybenzylidene)cyclohexanone were also used. The synthesized poly(ester amides) were characterized by qualitative solubility test, FT-IR, 1H and 13C NMR spectra. The monomeric moieties were found to be well incorporated in the polymer back bone. The molecular weight of the polymer was assessed by gel permeation chromatography (GPC). The thermal phase transition behavior and liquid crystallinity of the poly(ester amides) were investigated by differential thermogravimetry (DTG) and hot stage optical polarized microscopy (HOPM), respectively. Interestingly, these poly(ester amides) in dimethylacetamide were found to possess photo-crosslinking characteristics when irradiated by UV light. These polymeric materials may find utility value in optical information storage devices.

Intelligent structural color material based on WS2 nanosheets: applications for anti-counterfeiting

Structural color, an important functional component of many organisms, is widespread in the natural world. The value of WS2 is being gradually recognized. Inspired by these phenomena, an intelligent structural color material, with a heterogeneous striped pattern that is based on WS2 nanosheets, is presented here. When irradiated with light, the material is endowed with light-controlled, reversible, bending behavior with self-reporting color indication. Furthermore, the material has a high stability index and a small maximum bending angle. Most interestingly, because of the WS2 nanosheets’ strong photoluminescence ability, the structural colors’ intensity is increased. This material can be used as light-triggered, dynamic barcode labels for anti-counterfeiting different products. These features of the bioinspired structural color stripe pattern of the material indicate its potential for constructing binary information storage devices, intelligent sensors, and so on.

The Origin of Prebiotic Information System in the Peptide/RNA World: A Simulation Model of the Evolution of Translation and the Genetic Code.

Information is the currency of life, but the origin of prebiotic information remains a mystery. We propose transitional pathways from the cosmic building blocks of life to the complex prebiotic organic chemistry that led to the origin of information systems. The prebiotic information system, specifically the genetic code, is segregated, linear, and digital, and it appeared before the emergence of DNA. In the peptide/RNA world, lipid membranes randomly encapsulated amino acids, RNA, and peptide molecules, which are drawn from the prebiotic soup, to initiate a molecular symbiosis inside the protocells. This endosymbiosis led to the hierarchical emergence of several requisite components of the translation machine: transfer RNAs (tRNAs), aminoacyl-tRNA synthetase (aaRS), messenger RNAs (mRNAs), ribosomes, and various enzymes. When assembled in the right order, the translation machine created proteins, a process that transferred information from mRNAs to assemble amino acids into polypeptide chains. This was the beginning of the prebiotic information age. The origin of the genetic code is enigmatic; herein, we propose an evolutionary explanation: the demand for a wide range of protein enzymes over peptides in the prebiotic reactions was the main selective pressure for the origin of information-directed protein synthesis. The molecular basis of the genetic code manifests itself in the interaction of aaRS and their cognate tRNAs. In the beginning, aminoacylated ribozymes used amino acids as a cofactor with the help of bridge peptides as a process for selection between amino acids and their cognate codons/anticodons. This process selects amino acids and RNA species for the next steps. The ribozymes would give rise to pre-tRNA and the bridge peptides to pre-aaRS. Later, variants would appear and evolution would produce different but specific aaRS-tRNA-amino acid combinations. Pre-tRNA designed and built pre-mRNA for the storage of information regarding its cognate amino acid. Each pre-mRNA strand became the storage device for the genetic information that encoded the amino acid sequences in triplet nucleotides. As information appeared in the digital languages of the codon within pre-mRNA and mRNA, and the genetic code for protein synthesis evolved, the prebiotic chemistry then became more organized and directional with the emergence of the translation and genetic code. The genetic code developed in three stages that are coincident with the refinement of the translation machines: the GNC code that was developed by the pre-tRNA/pre-aaRS /pre-mRNA machine, SNS code by the tRNA/aaRS/mRNA machine, and finally the universal genetic code by the tRNA/aaRS/mRNA/ribosome machine. We suggest the coevolution of translation machines and the genetic code. The emergence of the translation machines was the beginning of the Darwinian evolution, an interplay between information and its supporting structure. Our hypothesis provides the logical and incremental steps for the origin of the programmed protein synthesis. In order to better understand the prebiotic information system, we converted letter codons into numerical codons in the Universal Genetic Code Table. We have developed a software, called CATI (Codon-Amino Acid-Translator-Imitator), to translate randomly chosen numerical codons into corresponding amino acids and vice versa. This conversion has granted us insight into how the genetic code might have evolved in the peptide/RNA world. There is great potential in the application of numerical codons to bioinformatics, such as barcoding, DNA mining, or DNA fingerprinting. We constructed the likely biochemical pathways for the origin of translation and the genetic code using the Model-View-Controller (MVC) software framework, and the translation machinery step-by-step. While using AnyLogic software, we were able to simulate and visualize the entire evolution of the translation machines, amino acids, and the genetic code.

Microwave-driven dynamic switching of the radial vortex in a nanodot by micromagnetic simulation

In this study, we investigate the reversal of a radial vortex under a microwave field by means of micromagnetic simulations. As a new nanoscale magnetization configuration with topologically protected stability, the radial vortex easily finishes reversal around some frequencies, which respond to the eigenfrequencies of the radial vortex. At a lower eigenfrequency, the reversal process is conducted by the breathing mode. At higher eigenfrequenies, the reversal happens due to the mixed modes (including the breathing mode and the radial spin-wave mode). For the breathing mode, the radial vortex radially expands and shrinks around the core region. For the two mixed modes, the spin excitation emerges around the core and edge of the radial vortex, and the magnetization reverses more dramatically than in the breathing mode. In one of the mixed modes, the radial vortex core reverses via a transient uniform state. These results all have potential applications for information storage devices.

Antiferromagnetic NiO atomic chains for information storage and the enhancement of inter-chain spin coupling by CO adsorption

One-dimensional antiferromagnetic atomic chains have potential applications in information storage and spintronics devices. NiO chains have been assembled on the Ni(110) single crystal surface, and the antiferromagnetic spin order has been determined by the first-principles calculations. Scanning tunneling microscope simulation clearly distinguishes two types of Ni with opposite spin-orientations. Therefore, the information carried by such system is possible to be read out. Furthermore, we have introduced the CO molecules, which zipper the neighboring NiO chains and greatly enhance the inter-chain spin coupling. The incorporation of CO has been verified by the low energy electron diffraction and the infrared spectroscopy.

Graphene-oxide/TiO2 nanocomposite films with electron-donors for multicolor holography.

Graphene oxide (GO) with an ideal two-dimensional structure, presents outstanding optical, electric, and mechanical properties which draws great attention in advanced information devices. Recently, GO-based films were found to show photochromic behavior, especially for the TiO2 involved system which has potential data processing capability, such as storing holograms. However, expanding spectral response range and increasing exposure sensitivity are still challenges for such a film, due to the limited photo-quantum efficiency in reduction reaction. Here, an innovative method of "Immersion-Dropping" technology is proposed to fabricate GO-based continuous films. We, for the first time, achieve colored holography from violet to yellow regions on GO/TiO2 nanocomposite films with introduction of weak acid molecules. A "diffraction self-enhancement" is observed. The obtained results benefit from the broadband photo-response of weak acid molecules and photo-triggered transferring of electrons in multi-channels. This work provides a research strategy for the large-capacity information storage and colorful display device.

A novel information storage and visual expression device based on mechanoluminescence

A novel information storage and visual expression device records the pre-stressed region and expresses the information via light emission.

Structural transformations and physical properties of (1 − x) Na0.5Bi0.5TiO3 − x BaTiO3 solid solutions near a morphotropic phase boundary

Piezoelectric and other physical properties are significantly enhanced at (or near) a morphotropic phase boundary (MPB) in ferroelectrics. MPB materials have attracted significant attention owing to both fundamental physics as well as the possibility of well-regulated energy and information storage devices which are dominated by lead (Pb)-based materials. Here, we report the crystal structure, Raman spectra, dielectric constant and polarization near the MPB of lead free (1 − x) Na0.5Bi0.5TiO3 − x BaTiO3 (0.00 ⩽ x ⩽ 0.10) solid-solution, prepared by sol–gel auto combustion technique and sintered by microwave sintering technique. With the addition of BaTiO3 into Na0.5Bi0.5TiO3, it induces a structural phase transition from R3c (a single phase) to R3c + P4mm (a dual phase) close to x = 0.06 and 0.07 and transform to a high symmetry tetragonal phase P4mm at higher compositions (x = 0.08 to 0.10) as evident from our x-ray Rietveld refinement and Raman spectroscopic results. We perform first-principles calculations based on density functional theory that confirm a structural transition from a rhombohedral to a tetragonal phase under increasing x. In the prepared solid solution, an anomalous enhancement of remnant polarization () was observed for x = 0.06 and 0.07, which has been explained based on the existence of the MPB. On the other hand, the value of coercive field was found to be decreased linearly from x = 0.00 to 0.06; it is constant for higher compositions. Further details of the ferroelectric properties on the electric field poled samples have been studied and compared with the as-grown (unpoled) samples.

Room-temperature nonvolatile four-state memory based on multiferroic Sr3Co2Fe21.6O37.4

Single-phase multiferroic hexaferrite Sr3Co2Fe21.6O37.4 was prepared by using a conventional solid-state reaction. The maximum electric polarization and magnetoelectric coefficient were Pm = 12.8 μC/m2 and αm = 600 ps/m, respectively. We found that the as-prepared specimen exhibited four different electric phase states from 0 to 1 T. Furthermore, the magnetic field and electric field poled the specimen's four different electric phase states and exhibited four different magnetoelectric effects. Based on these characteristics, a nonvolatile four-state memory device was implemented at room temperature. The information is written by the magnetic field and electric field in the poling process and read out by αm with a small scanning field. This kind of nonvolatile four-state memory device has the benefits of having a simple structure and high storage density, it is easy to integrate, and it can be performed at room temperature. Our work enriched the magnetoelectric effect of Sr3Co2Fe24O41 and will promote the application of multiferroic hexaferrites for information storage devices.

Synthesis and properties of stimuli-responsive ferrocene-and azobenzene-based copolymers P(FHEMA-co-MAAT)s

Three novel polymers (P(FHEMA-co-MAAT)s) having redox and photoresponsive moieties were prepared by free radical polymerization. The structures and molecular weights of the synthesized copolymers were characterized by nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC) respectively. Thermal properties, optical features and electroactive properties were studied with the help of thermogravimetric (TG), differential thermogravimetric (DTG) analysis, ultraviolet-visible spectroscopy (UV-vis) and cyclic voltammetry (CV). It was seen that synthesized copolymers had excellent redox and photoresponsive properties. These results exhibited that these polymers can be applied further for redox/photo responsive information storage devices.

Rhombohedral-Orthorhombic Ferroelectric Morphotropic Phase Boundary Associated with a Polar Vortex in BiFeO3 Films.

Strongly correlated oxides exhibit multiple degrees of freedoms, which can potentially mediate exotic phases with exciting physical properties, such as the polar vortex recently found in ferroelectric oxide films. A polar vortex is stabilized by competition between charge, lattice, and/or orbital degrees of freedom, which displays vortex-ferroelectric phase transitions and emergent chirality, making it a potential candidate for designing information storage and processing devices. Here, by a combination of controlled film growth and aberration-corrected scanning transmission electron microscopy, we obtain nanoscale vortex arrays in [110]-oriented BiFeO3 films. These vortex arrays are stabilized in ultrathin BiFeO3 layers sandwiched by two coherently grown orthorhombic scandate layers, exhibiting a ferroelectric morphotropic phase boundary constituted by a mixed-phase structure of polar orthorhombic BiFeO3 and rhombohedral BiFeO3. Clear polarization switching and piezoelectric signals were observed in these multilayers as revealed by piezoresponse force microscopy. This work presents a feature of a polar vortex in BiFeO3 films showing morphotropic phase boundary character, which offers a potential degree of manipulating phase components and properties of ferroelectric topological structures.

Reversible Mechanochromic Delayed Fluorescence in 2D Metal-Organic Micro/Nanosheets: Switching Singlet-Triplet States through Transformation between Exciplex and Excimer.

Mechanochromic luminescent materials have attracted much attention and present a variety of applications in information security, data recording, and storage devices. However, most of these smart luminescent systems are based on typical fluorescence and/or phosphorescence mechanisms; the mechanochromic delayed fluorescence (MCDF) materials involving switching singlet and triplet states are rarely studied to date. Herein, new 2D layered metal–organic micro/nanosheets, [Cd(9‐AC)2(BIM)2] (named as MCDF‐1; 9‐AC = anthracene‐9‐carboxylate and BIM = benzimidazole) and its solvate form containing interlayer CH3CN (named as MCDF‐2), which exhibit reversible mechanochromic delayed fluorescence characteristics, are presented. With applying the mechanical force, the luminescent center of MCDF‐1 can be converted from 9‐AC/BIM exciplex to 9‐AC/9‐AC excimer, resulting in alternations of delayed fluorescence. Such luminescent change can be further recovered by CH3CN fumigation, accompanied by the structural transformation from MCDF‐1 to MCDF‐2. Furthermore, the force‐responsive process also refers to the energy redistribution between singlet and triplet states as inferred by both temperature‐dependent photophysics and theoretical calculations. Therefore, this work not only develops new 2D micro/nanosheets as MCDF materials, but also supplies a singlet–triplet energy switching mechanism on their reversible mechanochromic process.

Entanglement and teleportation between polarization and wave-like encodings of an optical qubit

Light is an irreplaceable means of communication among various quantum information processing and storage devices. Due to their different physical nature, some of these devices couple more strongly to discrete, and some to continuous degrees of freedom of a quantum optical wave. It is therefore desirable to develop a technological capability to interconvert quantum information encoded in these degrees of freedom. Here we generate and characterize an entangled state between a dual-rail (polarization-encoded) single-photon qubit and a qubit encoded as a superposition of opposite-amplitude coherent states. We furthermore demonstrate the application of this state as a resource for the interfacing of quantum information between these encodings. In particular, we show teleportation of a polarization qubit onto a freely propagating continuous-variable qubit.

Ag-Sensitized Yb3+ Emission in Glass-Ceramics.

Rare earth doped materials play a very important role in the development of many photonic devices, such as optical amplifiers and lasers, frequency converters, solar concentrators, up to quantum information storage devices. Among the rare earth ions, ytterbium is certainly one of the most frequently investigated and employed. The absorption and emission properties of Yb3+ ions are related to transitions between the two energy levels 2F7/2 (ground state) and 2F5/2 (excited state), involving photon energies around 1.26 eV (980 nm). Therefore, Yb3+ cannot directly absorb UV or visible light, and it is often used in combination with other rare earth ions like Pr3+, Tm3+, and Tb3+, which act as energy transfer centres. Nevertheless, even in those co-doped materials, the absorption bandwidth can be limited, and the cross section is small. In this paper, we report a broadband and efficient energy transfer process between Ag dimers/multimers and Yb3+ ions, which results in a strong PL emission around 980 nm under UV light excitation. Silica-zirconia (70% SiO2-30% ZrO2) glass-ceramic films doped by 4 mol.% Yb3+ ions and an additional 5 mol.% of Na2O were prepared by sol-gel synthesis followed by a thermal annealing at 1000 °C. Ag introduction was then obtained by ion-exchange in a molten salt bath and the samples were subsequently annealed in air at 430 °C to induce the migration and aggregation of the metal. The structural, compositional, and optical properties were investigated, providing evidence for efficient broadband sensitization of the rare earth ions by energy transfer from Ag dimers/multimers, which could have important applications in different fields, such as PV solar cells and light-emitting near-infrared (NIR) devices.