High-density Information Storage Research Articles

Significant enhancement of magnetic anisotropy and conductivity in GaN/CrI3 van der Waals heterostructures via electrostatic doping

van der Waals magnetic heterostructures, consisting of a wide band-gap nitride semiconductor and an intrinsic ferromagnetic semiconductor, are potentially useful for low-dimensional spintronic field-effect transistors. However, there is a significant challenge. For instance, the integration often leads to a decreased Curie temperature, the magnetic anisotropy direction change, and low conductivities. Here, we employ the first-principles density-functional method to systematically investigate the electronic and magnetic properties of the $\mathrm{GaN}/{\mathrm{CrI}}_{3}$ van der Waals heterostructures under electrostatic doping. Though the easy magnetization axis of the monolayer ${\mathrm{CrI}}_{3}$ transforms from out-of-plane to in-plane direction over 0.2 electron doping per unit cell, the $\mathrm{GaN}/{\mathrm{CrI}}_{3}$ van der Waals heterostructure maintains perpendicular anisotropy under electron doping, crucial for high-density information storage. The Curie temperature of the $\mathrm{GaN}/{\mathrm{CrI}}_{3}$ van der Waals heterostructure can be enhanced under both electron and hole doping. The $\mathrm{GaN}/{\mathrm{CrI}}_{3}$ van der Waals heterostructure presents half-metallic properties and the spin-up conductivities are much larger than that of the monolayer ${\mathrm{CrI}}_{3}$ under the same electrostatic doping. Our results indicate that constructing heterostructures with ferromagnets and nonmagnetic semiconductors is an effective strategy for developing high-performance field-effect transistors.

Spontaneous Topological Magnetic Transitions in NdCo5 Rare-Earth Magnets.

Particle-like magnetic textures with nanometric sizes, such as skyrmions, are potentially suitable for designing high-efficiency information bits in future spintronics devices. In general, the Dzyaloshinskii-Moriya interactions and dipolar interactions are the dominant factors for generating nonlinear spin configurations. However, to stabilize the topological skyrmions, an external magnetic field is usually required. In this study, the spontaneous emergence of skyrmions is directly observed, together with the unique successive topological domain evolution during the spin reorientation transition in a neodymium-cobalt (NdCo5 ) rare-earth magnet. On decreasing the temperature, nanometric skyrmion lattices evolve into enclosed in-plane domains (EIPDs) similar to mini bar-magnets with size below 120nm. The internal magnetization rotates with magnetic anisotropy, demonstrating the ability to manipulate the mini bar-magnets. The nanoscale EIPD lattices remain robust over the wide temperature range of 241-167 K, indicating the possibility of high-density in-plane magnetic information storage. The generation of spontaneous magnetic skyrmions and the successive domain transformation in the traditional NdCo5 rare-earth magnet may prompt application exploration for topological magnetic spin textures with novel physical mechanisms in versatile magnets.

Dual-color meta-image display with a silver nanopolarizer based metasurface

Plasmonic metallic nanostructures with anisotropic design have unusual polarization-selective characteristic which can be utilized to build nanopolarizers at the nanoscale. Herein, we propose a dual-color image display platform by reconfiguring two types of silver nanoblocks in a single-celled metasurface. Governed by Malus's law, the two types of silver nanoblocks both acting as nanopolarizers with different orientations can continuously modulate the intensity of incident linearly polarized red and green light pixel-by-pixel, respectively. As a result, an ultra-compact, high-resolution, and continuous-greyscale dual-color image can be recorded right at the surface of the meta-device. We demonstrate the dual-color Malus metasurface by successfully encoding and decoding a red-green continuously-grayscale image into a metasurface sample. The experimentally captured meta-image with high-fidelity and resolution as high as 63500 dots per inch (dpi) has verified our proposal. With the advantages such as continuous grayscale modulation, ultrathin, high stability and high density, the proposed dual-color encoded metasurfaces can be readily used in ultra-compact image displays, high-end anti-counterfeiting, high-density optical information storage and information encryption, etc.

Phase-field simulations of surface charge-induced ferroelectric vortex

Ferroelectric vortices are characterized by their small size and exotic physical properties, which have great potential for application in high-density information storage. However, the influence of the shape of the external field on such topological vortex domain morphology and domain percentage is still lacking research. Here, the ferroelectric domain evolution induced by a circular-, square-, and triangular-shaped surface charge are investigated in BiFeO3 thin films by phase-field simulations. The shape symmetry of the surface charge distribution determines the 4R domain percentage in one single vortex. Triangle-shaped surface charge distribution with odd number symmetry axes has the greatest influence on the percentage of 4R domain, while that of circular- and square-shaped with even number symmetry axes have almost no influence on the 4R domain ratio. Compared to the triangle, an antivortex can be observed around the vortex domain in the circular- and square-shaped surface charge. The rotating triangle affects the domain percentage of the vortex and the emergence of an antivortex. Here, the difference of domain percentage is determined by the choice of nucleation position and the domain switching mechanism. It was found that the percentage of domain along the edge is greater than the corner of the triangle. Among them, 71° domain switching is more likely to happen than 109° and 180° domain switching. These findings provide a fundamental understanding for ferroelectric domain manipulation in a single vortex from an external field with different shapes.

Front Cover: Slow Magnetic Relaxation in Mono‐ and Bimetallic Lanthanide Tetraimido‐Sulfate S(NtBu)42− Complexes (Chem. Eur. J. 48/2021)

Single-molecule magnets (SMMs) have great potential application in a range of pioneering areas, such as quantum computing, spintronics, and high-density information storage. The properties of the molecules presented here are based on the molecular total spin and the magnetic anisotropy created by the lanthanides in a particular crystal field. An important element in SMMs’ optimization is the ligand design. Poly imido sulfur ligands are perfectly suited as the polar S+−N−-bond facilitates electronic and geometric adaptability to various f-metals. Particularly the acute N–Dy–N bite angle generates advantageous magnetic properties. More information can be found in the Full Paper by S. Demir, D. Stalke et al. (DOI: 10.1002/chem.202101076).

High-density information storage and random access scheme using synthetic DNA.

The high-storage density, long-life cycle, and low-energy consumption of DNA molecules make it the future of next-generation storage technology. However, DNA storage has the disadvantages of high-synthesis cost and low-random access efficiency. A high-density DNA-coding scheme can effectively reduce the cost of DNA synthesis. This paper first proposes a DNA-mapping method based on codebook and a random access method for DNA information based on encoded content. The mapping method satisfies the two biological constraints of homopolymer length and GC content. The random access method can efficiently and selectively read specific files in the DNA pool. To increase storage density, convolutional neural networks are combined with mapping methods to generate base sequences. In the experiments, our method was compared with the results of existing DNA information storage methods, which showed that the proposed scheme has better information storage density.

Single-celled multifunctional metasurfaces merging structural-color nanoprinting and holography.

Nanostructured metasurfaces applied in structural-color nanoprinting and holography have been extensively investigated in the past several years. Recently, merging them together is becoming an emerging approach to improve the information capacity and functionality of metasurfaces. However, current approaches, e.g., segmenting, interleaving and stacking schemes for function merging, suffer from crosstalk, low information density, design and fabrication difficulties. Herein, we employ a single-celled approach to design and experimentally demonstrate a high-density multifunctional metasurface merging nanoprinting and holography, i.e., each nanostructure in the metasurface can simultaneously manipulate the spectra (enabled with varied dimensions of nanostructures) and geometric phase (enabled with varied orientation angles of nanostructures) of incident light. Hence, with different decoding strategies, a structural-color nanoprinting image emerges right at the metasurface plane under white light illumination, while a holographic image is reconstructed in the Fraunhofer diffraction zone under circularly polarized laser light incidence. And the two images have no crosstalk since they are independently designed and presented at different distances. Our proposal suggests a space-multiplexing scheme to develop advanced metasurfaces and one can find their markets in high-density information storage, optical information encryption, multi-channel image display, etc.

Toward next-generation optical disks

Nano-Optical Writing Subdiffraction information bits can be written using superresolution methods to achieve extremely high-density information storage. Using lanthanide-doped upconversion nanoparticles to locally reduce graphene oxide flakes through upconversion resonance energy transfer upon engineered illumination, Lamon et al. achieved an estimated storage capacity of 700 terabytes on a 12-centimeter optical disk by nanoscale optical writing, comparable to a storage capacity of 28,000 single-layer Blu-ray disks. This technology offers an inexpensive solution for the next generation of high-capacity optical data storage and enables energy-efficient nanofabrication of flexible, graphene-based electronics. Sci. Adv. 10.1126/sciadv.abe2209 (2021).

α-Cyanoarylethene ferrocene based rod-shaped compounds, synthesis, self-assembly and redox-responsive properties

A series of novel α-cyanoarylethene ferrocene based rod-shaped compounds consisting of a biphenyl rigid core, connected with multi-alkyl chain substituted benzene unit via ether (–OCH2-) or ester (-OOC-) link at one end, and with ferrocene unit through α-cyano arylethene at the other end were prepared via Suzuki coupling and Knoevenagel condensation reactions as key steps. The effects of the length and number of the alkyl chain as well as the linking groups on the self-assembly properties of these compounds in bulk states and in organic solutions were investigated. In bulk sate, only the single tetradecyl chain compound with ester (-OOC-) link can show liquid crystalline property, while in organic solvents, such compounds can self-assemble into gels with interesting morphologies. Cyclic voltammetry (CV) and Ultraviolet-visible (UV–vis) absorption studies demonstrated redox characteristics of the prepared compounds. Most interesting is the PEG (polyethylene glycol) film containing such compound (1–5%) was observed to be redox sensitive. The color of the prepared film could be regulated by the redox stimulation, indicating such PEG film have potential for high density information storage.

Molecular structures and magnetic properties of endohedral metallofullerenes.

Endohedral metallofullerenes have fascinating core-shell structures, with metal atoms or metal clusters encaged in fullerene cages, and they display various chemical, optical and magnetic properties derived from different types of fullerene cages and metal moieties. Fullerene cages can act as carriers to stabilize unusual cluster moieties. Many bizarre species that are hard to produce via synthetic methods survive well under the protection of a fullerene cage, making metallofullerenes ideal platforms for generating new clusters and bonds. Fullerene cages can also be carriers to hold active unpaired electrons. Some metallofullerenes possess electron spin and show intriguing magnetic properties, making them applicable for use in quantum computing, high density information storage and magnetoreception systems. The exploration of new metallofullerenes is still ongoing, while function-oriented studies are also promoted for the future application of metallofullerenes. Herein, we highlight the recent progress in the synthesis, electron spin characteristics and magnetic properties of metallofullerenes. Discussions and an outlook on the future development of metallofullerenes are also stated.

Effects of Various Sintering Conditions on the Structural and Magnetic Properties of Zinc Ferrite (ZnFe2O4)

Abstract Zinc ferrite (ZnFe2O4) nanoparticles have attracted the attention of researchers because of their unique chemical properties and particle-size-dependent magnetic properties. High-surface-area spinel ferrites have numerous technical applications in areas such as high-density information storage, ferrofluids, and catalysis. The coprecipitation technique is the preferred method for preparing nanoscale ZnFe2O4 because it results in a small crystals with a uniform size distribution. In this study, the synthesis was conducted in solution for 48 h, followed by sintering at 1000°C for 1.5–3.5 h. The smallest crystals (70.58 nm) were found in the sample sintered for 2.5 h. Fourier transform infrared spectroscopy (FTIR) functional-group analysis confirmed the presence of Fe–O and Zn–O bonds of cations in octahedral and tetrahedral sites. The ZnFe2O4 sintered for 3.5 h was superparamagnetic. The characterization results suggest that the obtained ZnFe2O4 could be used as a nanofluid in heat exchangers.

Giant perpendicular magnetic anisotropy induced by double degeneracy of d-orbitals in W/MgO/Ag heterojunction

Large perpendicular magnetic anisotropy energy (MAE) is crucial for designing high-density information storage devices. Here, employing first-principles calculations, it has shown the possibility to boost the magnetic anisotropy using a single W atom functionalized by radical of hydroxy (OH) on the MgO(001)/Ag(001) heterojunction. The OH-functionalized system exhibited the giant perpendicular MAE of 214.76 meV, which outperformed all the reported heterojunctions. The underlying mechanism for the enormous MAE is attributed to the doubly degenerated d-orbitals around the Fermi level caused by a special OH-ligand field which alters the spin-orbit coupling Hamiltonian and enhances the magnetic anisotropy. Meanwhile, the small spin magnetic moment of 1.829 μB is obtained due to the strong OH-ligand field. This work provides a new approach to generate high perpendicular MAE that is very promising for nanoscale magnetic devices.

Overview of the Role of Alloying Modifiers on the Performance of Phase Change Memory Materials

Phase change memory (PCM) based on chalcogenide compounds is considered to be an excellent candidate for next-generation memory because of its high speed, low energy consumption, high-density information storage, and durable stability. This has become a topic of general interest during the last two decades. Various systems have been proposed to explore more suitable compositions for PCM applications such as Ge-Te and Sb-Te binary alloys, GeTe-Sb2Te3 pseudo-binary alloys, and novel Te-free Sb-based alloys. In spite of this, the comprehensive performance of these pure systems still cannot fully satisfy the need for commercialization. Modification of alloys is an effective approach to enhance performance; this has been investigated significantly. Nevertheless, there are relatively few reports that directly provide integrated data on the effect of various alloying modifiers on the properties of PCM materials to obtain the relevant information conveniently, understand the role of chemical tailors on the properties of PCM materials deeply, and select modifiers matching the matrix systems efficiently. To achieve these goals and facilitate studies on PCM materials, this overview begins by summarizing and analyzing the role of alloying tailors on the performance of representative GeTe, Sb2Te3, Ge2Sb2Te5, and Sb-based systems containing Te (Sb2Te, Sb3Te, Sb4Te) and without Te (Sb-M), followed by comparing the comprehensive performance of optimized systems.

Observation of single-defect memristor in an MoS2 atomic sheet.

Non-volatile resistive switching, also known as memristor1 effect, where an electric field switches the resistance states of a two-terminal device, has emerged as an important concept in the development of high-density information storage, computing and reconfigurable systems2-9. The past decade has witnessed substantial advances in non-volatile resistive switching materials such as metal oxides and solid electrolytes. It was long believed that leakage currents would prevent the observation of this phenomenon for nanometre-thin insulating layers. However, the recent discovery of non-volatile resistive switching in two-dimensional monolayers of transition metal dichalcogenide10,11 and hexagonal boron nitride12 sandwich structures (also known as atomristors) has refuted this belief and added a new materials dimension owing to the benefits of size scaling10,13. Here we elucidate the origin of the switching mechanism in atomic sheets using monolayer MoS2 as a model system. Atomistic imaging and spectroscopy reveal that metal substitution into a sulfur vacancy results in a non-volatile change in the resistance, which is corroborated by computational studies of defect structures and electronic states. These findings provide an atomistic understanding of non-volatile switching and open a new direction in precision defect engineering, down to a single defect, towards achieving the smallest memristor for applications in ultra-dense memory, neuromorphic computing and radio-frequency communication systems2,3,11.

Reading and Writing Digital Information in TNA.

DNA has become a popular soft material for low energy, high-density information storage, but it is susceptible to damage through oxidation, pH, temperature, and nucleases in the environment. Here, we describe a new molecular chemotype for data archiving based on the unnatural genetic framework of α-l-threofuranosyl nucleic acid (TNA). Using a simple genetic coding strategy, 23 kilobytes of digital information were stored in DNA-primed TNA oligonucleotides and recovered with perfect accuracy after exposure to biological nucleases that destroyed equivalent DNA messages. We suggest that these results extend the capacity for nucleic acids to function as a soft material for low energy, high-density information storage by providing a safeguard against information loss caused by nuclease digestion.

HEDGES error-correcting code for DNA storage corrects indels and allows sequence constraints

Synthetic DNA is rapidly emerging as a durable, high-density information storage platform. A major challenge for DNA-based information encoding strategies is the high rate of errors that arise during DNA synthesis and sequencing. Here, we describe the HEDGES (Hash Encoded, Decoded by Greedy Exhaustive Search) error-correcting code that repairs all three basic types of DNA errors: insertions, deletions, and substitutions. HEDGES also converts unresolved or compound errors into substitutions, restoring synchronization for correction via a standard Reed-Solomon outer code that is interleaved across strands. Moreover, HEDGES can incorporate a broad class of user-defined sequence constraints, such as avoiding excess repeats, or too high or too low windowed guanine-cytosine (GC) content. We test our code both via in silico simulations and with synthesized DNA. From its measured performance, we develop a statistical model applicable to much larger datasets. Predicted performance indicates the possibility of error-free recovery of petabyte- and exabyte-scale data from DNA degraded with as much as 10% errors. As the cost of DNA synthesis and sequencing continues to drop, we anticipate that HEDGES will find applications in large-scale error-free information encoding.

Ultracompact metaimage display and encryption with a silver nanopolarizer based metasurface

Governed by the Malus law, nanopolarizer-based metasurfaces can continuously modulate the intensity of incident linearly polarized (LP) light pixel-by-pixel, which has been applied to display metaimages with ultracompactness and high resolution. One unique characteristic of the Malus-assisted image display technique is that no matter the polarization direction of incident LP light, the image with different contrast always appears, which would affect the security of a metaimage. Here, inspired by the orientation degeneracy of the Malus law, we show that metaimage displays can be controlled in two fixed polarization directions, merely by reconfiguring the orientations of nanopolarizers. Specifically, for each metaimage pixel, there are two options for the orientation angle of the nanopolarizer corresponding to an equal grayscale value. By randomly selecting the orientation angle among two choices, the metaimage will be blurred or even hidden, except for the polarization direction of 0° for the original image and 90° for its contrast reversed partners. We experimentally demonstrate this concept by encoding a Lena image with pixels of 1000 × 1000 into a silver nanopolarizer-based metasurface and decoding/encrypting it in a polarization-controlled optical setup. The proposed metaimage display with the encryption functionality has advantages such as continuous grayscale modulation, ultrathinness, and high density, which can be applied in ultracompact image displays, high-end anti-counterfeiting, high-density optical information storage, information encryption, etc.

Interfacial tuning of chiral magnetic interactions for large topological Hall effects in LaMnO3/SrIrO3 heterostructures.

Chiral interactions in magnetic systems can give rise to rich physics manifested, for example, as nontrivial spin textures. The foremost interaction responsible for chiral magnetism is the Dzyaloshinskii-Moriya interaction (DMI), resulting from inversion symmetry breaking in the presence of strong spin-orbit coupling. However, the atomistic origin of DMIs and their relationship to emergent electrodynamic phenomena, such as topological Hall effect (THE), remain unclear. Here, we investigate the role of interfacial DMIs in 3d-5d transition metal-oxide-based LaMnO3/SrIrO3 superlattices on THE from a chiral spin texture. By additively engineering the interfacial inversion symmetry with atomic-scale precision, we directly link the competition between interfacial collinear ferromagnetic interactions and DMIs to an enhanced THE. The ability to control the DMI and resulting THE points to a pathway for harnessing interfacial structures to maximize the density of chiral spin textures useful for developing high-density information storage and quantum magnets for quantum information science.

Rational design of 2D organic magnets with giant magnetic anisotropy based on two-coordinate 5d transition metals

As a new class of single-molecule magnets, two-coordinate complexes of open-shell transition metals are comparatively rare and have attracted interest due to their high degree of coordinative unsaturation. However, the dynamic distortion associated with the low coordination number of the metal center hinders the applications of high-density information storage, quantum computing, and spintronics. Here, we propose a series of stable 2D metal–organic frameworks constructed by ideal (1, 3, 5)-benzenetricarbonitrile (TCB) molecules and 5d transition metals (Hf, Ta, W, Re, Os, and Ir) with a highly symmetrical ligand field and rigid π conjugated framework. Among them, TCB-Re exhibits intrinsic ferromagnetic ordering with a considerably large magnetic anisotropic energy (MAE) of 19 meV/atom and high Curie temperature (TC) of 613 K. Under biaxial strain, diverse magnetic states (such as ferromagnetic, paramagnetic, and antiferromagnetic states) can be achieved in TCB-Re by the complicated competition between the in-plane d–px/y–d and out-of-plane d–pz–d superexchange interactions. At a small compressive strain of 0.5%, the MAE for perpendicular magnetization increases substantially to 120 meV/atom; meanwhile, the magnetization and TC above room temperature are well retained. Our results not only extend two-coordinate transition metal complexes to continuous 2D organic magnets but also demonstrate an effective method of strain engineering for manipulating the spin state and MAE.

Room-temperature skyrmions in strain-engineered FeGe thin films

Skyrmions hold great promise for low-energy consumption and stable high-density information storage, and stabilization of the skyrmion lattice (SkX) phase at or above room temperature is greatly desired for practical use. The topological Hall effect can be used to identify candidate systems above room temperature, a challenging regime for direct observation by Lorentz electron microscopy. Atomically ordered FeGe thin films are grown epitaxially on Ge(111) substrates with $\ensuremath{\sim}4%$ tensile strain. Magnetic characterization reveals enhancement of the Curie temperature to 350 K due to strain, well above the bulk value of 278 K. A strong topological Hall effect was observed between 10 and 330 K, with a significant increase in magnitude observed at 330 K. The increase in magnitude occurs just below the Curie temperature, similar to the onset of the SkX phase in bulk FeGe. The results suggest that strained FeGe films may host a SkX phase above room temperature when significant tensile strain is applied.