Information Storage Devices Research Articles

Pressure‐Driven Two‐Step Second‐Harmonic‐Generation Switching in BiOIO3

AbstractMaterials with multi‐stabilities controllable by external stimuli have potential for high‐capacity information storage and switch devices. Herein, we report the observation of pressure‐driven two‐step second‐harmonic‐generation (SHG) switching in polar BiOIO3 for the first time. Structure analyses reveal two pressure‐induced phase transitions in BiOIO3 from the ambient noncentrosymmetric phase (SHG‐high) to an intermediate noncentrosymmetric phase (SHG‐intermediate) and then to a centrosymmetric phase (SHG‐off). The three‐state SHG switching was inspected by in situ high‐pressure powder SHG and polarization‐dependent single‐crystal SHG measurements. Local structure analyses based on the in situ Raman spectra and X‐ray absorption spectra reveal that the SHG switching is caused by the step‐wise suppression of lone‐pair electrons on the [IO3]− units. The dramatic evolution of the functional units under compression also leads to subtle changes of the optical absorption edge of BiOIO3. Materials with switchable multi‐stabilities provide a state‐of‐art platform for next‐generation switch and information storage devices.

Pressure-Driven Two-Step Second-Harmonic-Generation Switching in BiOIO3.

Materials with multi-stabilities controllable by external stimuli have potential for high-capacity information storage and switch devices. Herein, we report the observation of pressure-driven two-step second-harmonic-generation (SHG) switching in polar BiOIO3 for the first time. Structure analyses reveal two pressure-induced phase transitions in BiOIO3 from the ambient noncentrosymmetric phase (SHG-high) to an intermediate noncentrosymmetric phase (SHG-intermediate) and then to a centrosymmetric phase (SHG-off). The three-state SHG switching was inspected by in situ high-pressure powder SHG and polarization-dependent single-crystal SHG measurements. Local structure analyses based on the in situ Raman spectra and X-ray absorption spectra reveal that the SHG switching is caused by the step-wise suppression of lone-pair electrons on the [IO3 ]- units. The dramatic evolution of the functional units under compression also leads to subtle changes of the optical absorption edge of BiOIO3 . Materials with switchable multi-stabilities provide a state-of-art platform for next-generation switch and information storage devices.

Prediction of the ferrovalley property with sizable valley splitting in Janus monolayer GdBrI.

The exploitation of two-dimensional (2D) ferrovalley materials is of great significance in promoting the development of novel information storage devices, which is garnering increasing interest nowadays. However, the currently discovered 2D ferrovalley materials are very limited, and some of them still suffer from the drawback of small valley splitting, which seriously hinders their application in valleytronics. Herein, using first-principles calculations, we predict a promising 2D ferrovalley material, Janus monolayer GdBrI, which harbors sizable valley splitting and the anomalous valley Hall effect (AVHE). Monolayer GdBrI is a stable ferromagnetic semiconductor with an easy magnetization plane and magnetic transition temperature of 264.5 K. When the magnetization orientation is toward the z direction, valley polarization with a large splitting of 120.4 meV is achieved in the valence band due to the synergetic effect between the magnetic exchange interaction and spin-orbit coupling. The valley-contrasting Berry curvature gives rise to the AVHE in the monolayer. The magnitude of valley splitting can be continuously tuned by varying the magnetization orientation, biaxial strain and perpendicular electric field. These findings offer Janus monolayer GdBrI as a potential candidate for spintronic and valleytronic applications.

Magnetoelectric coupling effects on the band alignments of multiferroic In2Se3-CrI3 trilayer heterostructures.

Due to unique magnetoelectric coupling effects, two-dimensional (2D) multiferroic van der Waals heterostructures (vdWHs) are promising for next-generation information processing and storage devices. Here, we design theoretically multiferroic In2Se3/CrI3 trilayer vdWHs with different stacking patterns. For the CrI3/In2Se3/CrI3 trilayer vdWHs, whether ferroelectric upward or downward polarization, type-I and type-II band alignments are formed for spin-up and spin-down channels. However, for the CrI3/In2Se3/In2Se3 trilayer vdWHs, downward polarization induces the type-III band alignment, which is typical for spin-tunnel transistors. Moreover, nonvolatile ferroelectric polarization and stacking patterns can induce the conversion between a unipolar semiconductor and a bipolar (unipolar) half-metal. These results provide a possible route to realize nanoscale multifunctional spintronic devices based on 2D multiferroic systems.

Effect of Buffer and Cap Layer on Thermally Stable Perpendicular Magnetic Anisotropy in Buffer/CoFeB/MgO/Cap Structure

The effect of buffer and cap layer on thermally stable perpendicular magnetic anisotropy (PMA) in buffer/CoFeB/MgO/cap structure was designed to detailed study. Not only the buffer layer is crucial, but the type of cap layer also affects the thermal stability of PMA. Relatively to the Ta samples, the W samples adopting W buffer or cap layer get a wider PMA thickness range for further increasing thermal stability of PMA in magnetic random access memory (MRAM) applications. And the same as the W buffer layer, the annealing temperature for W cap layer is also increased 30°C (from 270°C to 300°C). Via the detailed anomalous Hall effect (AHE) measurements, the thermal stability of PMA in buffer/CoFeB/MgO/cap was investigated. This work provides a promising way to obtain high thermal stability of PMA in CoFeB-MgO-based spintronic applications, and it is significant for designing the next-generation information storage devices.

Low magnetic-field induced high temperature dynamic magnetoelectric coupling performances in Z-type Sr3Co2Fe24O41

Magnetic-field induced dynamic magnetoelectric coupling effects and polarization performance of Z-type Sr3Co2Fe24O41 (SCFO) ceramic has been investigated. Results found that SCFO’s transverse tapered magnetic structure can induce electric polarization, and its electric polarization direction will not change under external magnetic effects. First-order dynamic magnetoelectric coupling coefficient (α) and second-order dynamic magnetoelectric coupling coefficient (β) of SCFO exhibited strong response main in magnetic structural phase transition region. The magnetoelectric structural phase transition position appeared in low magnetic field, and the magnetic moment vector and its corresponding electric polarization vector of SCFO exhibited the most unstable state near its equilibrium position, which is beneficial for inducing strong dynamic magnetoelectric coupling response. When the applied magnetic fields to SCFO increased, the magnetic moment stability near the equilibrium position increased, and the dynamic magnetoelectric coupling response decreased. Results showed that the dynamic magnetoelectric coupling response of SCFO can bear T 1 = 370 K high temperature. The dynamic magnetoelectric coupling response induced by low magnetic fields in SCFO contributes to its actual application in next generation magnetoelectric information storage devices.

Optimization of hydrogen-ion storage performance of tungsten trioxide nanowires by niobium doping

The transport and storage of ions within solid state structures is a fundamental limitation for fabricate more advanced electrochemical energy storage, memristor, and electrochromic devices. Crystallographic shear structure can be induced in the tungsten bronze structures composed of corner-sharing WO6 octahedra by the addition of edge-sharing NbO6 octahedra, which might provide more storage sites and more convenient transport channels for external ions such as hydrogen ions and alkali metal ions. Here, we show that Nb2O5·15WO3 nanowires (Nb/W = 0.008) with long length-diameter ratio, smooth surface, and uniform diameter have been successfully synthesized by a simple hydrothermal method. The Nb2O5·15WO3 nanowires do exhibit more advantages over h-WO3 nanowires in electrochemical hydrogen ion storage such as smaller polarization, larger capacity (71 mAh g−1, at 10C, 1C = 100 mA g−1), better cycle performance (remain at 99% of the initial capacity after 200 cycles at 100C) and faster H+ ions diffusion kinetics. It might be the crystallographic shear structure induced by Nb doping that does result in the marked improvement in the hydrogen-ion storage performance of WO3. Therefore, complex niobium tungsten oxide nanowires might offer great promise for the next generation of electrochemical energy and information storage devices.

Reversible Mechanically Induced On–Off Photoluminescence in Hybrid Metal Halides

AbstractStimulus‐responsive photoluminescent materials have attracted extensive research attention in recent years owing to their potential application in information storage and switch devices. It is important to further explore such bistable materials as well as the underlying transformation mechanisms. Herein, the syntheses and mechanically tunable “on–off” photoluminescence (PL) of two organic–inorganic hybrid metal halides, (Bmpip)9Pb3Zn2Br19 and (Bmpip)9Pb3Cd2Br19 (Bmpip+ = 1‐butyl‐1‐methyl‐piperidinium, C10H22N+), are reported. Both as‐obtained compounds are nonemissive under UV light at ambient conditions but exhibit bright PL upon grinding or under hydrostatic pressure. Interestingly, the PL is quenchable by short‐time annealing or storage in air for 1 week, and the process is repeatable. Through a combination of extensive structural and spectral analyses, the crucial role of the organic cations interacting with inorganic chromophores in the “on–off” PL behavior of the title compounds is revealed. Moreover, pressure‐induced PL and PL‐enhancement phenomena are observed in both compounds, which are similar to but slightly different than the above‐mentioned mechano‐PL. Finally, proof‐of‐concept devices are fabricated to demonstrate the potential applications of the title compounds in message recording and force sensing.

Facile preparation of high strength, lightweight and thermal insulation Polyetherimide/Ti3C2Tx MXenes/Ag nanoparticles composite foams for electromagnetic interference shielding

Novel PEI/Ti3C2Tx MXenes/Ag nanoparticles composite foams with high strength, low density, and thermal insulation characters have been developed by solution blended process and mold compression methods. The obtained PEI/Ti3C2Tx MXenes/Ag nanoparticles composite foams exhibited high electromagnetic interference shielding effectivity of 28 dB at 8.2–12.4 GHz with low Ti3C2Tx MXenes and Ag nanoparticles loading. Moreover, most of the applied microwave was verified to be absorbed rather than being reflected back. Meanwhile, this foam material possessed a low thermal conductivity of 0.029–0.053 W/(m∙K) and high mechanical strength of 11.59–20.20 MPa. This preparation method is fast, highly reproducible, and scalable, the obtained PEI/Ti3C2Tx MXenes/Ag nanoparticles composite foams with electromagnetic interference (EMI) shielding property may be used in the fields of packaging materials for information storage devices.

Ultrathin Metal–Organic Framework Nanosheets as Nano‐Floating‐Gate for High Performance Transistor Memory Device

AbstractMetal–organic framework (MOF) is an emerging important class of functional materials in the fields of information storage, wearable electronics and optoelectronic devices. The interaction of electrons or holes with MOFs is important for the systematic exploration of MOFtronics and to investigate the related structure–performance correlation. Herein, MOF flat nanosheets of copper tetrakis(4‐carboxyphenyl)porphyrin with sub‐10 nanometer scale in thickness are employed as the charge‐trapping layer in organic field‐effect floating‐gate transistor memory device fabricated by an air–liquid interfacial assembly and subsequent stamping operation. As charge trapping sites, MOF nanosheets with ultrathin nanoporous arrays significantly improve in comparison with the memory device using its counterpart ligand of tetrakis(4‐carboxyphenyl)porphyrin as the trapping elements. As compared to the reported widely applied nanofloating gate materials of gold nanoparticles, graphene, or macromolecular nanomaterials, a short pulse (≈20 ms) on the device gets a considerable memory window of ≈37.5 V at a programming voltage of ‐80 V, with a retention time longer than 104 s and good ON/OFF ratio of >103. Furthermore, the hybrid structure composed of metal and organic components endows it with electron and hole trapping capability. This work could push forward the fundamental research of organic–inorganic–hybrid electronics in future microelectronic research.

Ultrafast Photochromic Self‐Healing Polymer Gels with Tunable Fluorescence

AbstractPhotoresponsive self‐healing polymer gels have great potential in the fields of optical information storage, artificial intelligence, and wearable flexible devices. Herein, a series of photoresponsive self‐healing gels based on dynamic imine bonds are synthesized in which the photoresponsive functions are achieved by the incorporation of the chromophore 1,2‐bis(5′‐formyl‐2′‐methylthien‐3′‐yl)perfluorocyclopentene (DEA) and the fluorophore 2,5‐dimethoxybenzene‐1,4‐diformaldehyde derivatives (DBD) through the Schiff base reactions between DEA/DBD and aminopropylmethylsiloxane‐dimethylsiloxane copolymers. The gels show ultrafast photoresponsive ability with the transition from yellow to blue within 10 s under 254 nm UV–Vis and subsequent color restoration within 20 s under visible light, derived from the fast ring‐closure and ‐opening transition of DEA. Interestingly, the molecular states of DEA have influence on the on–off intensity of the fluorescence. The gels with ring‐opened DEA show stronger blue fluorescence than the ones with ring‐closed DEA. In addition, the cross‐linked dynamic imine bond enables the gels to self‐heal quickly, and the wound disappears within 10 min without any external stimuli.

Photoresponse of high quality epitaxial BiFeO3 films grown through hydrothermal method and rapid microwave assisted method

High quality BiFeO3 film with enhanced remanent polarization and magnetization attracts much interest for its great application potential in information storage and photoelectric devices. Here we grew single-crystal epitaxial BiFeO3 film on SrTiO3 substrate through hydrothermal method at low temperature, the film has a quality higher than any reported BiFeO3 films grown through hydrothermal method. Furthermore, BiFeO3 film was grown through a 25 min rapid microwave-assisted hydrothermal process. The two BiFeO3 films exhibited obvious light response to periodically switching on and off of a LED light, and the film grown through microwave-assisted hydrothermal method produced a 4.7V open-circuit voltage exceeding the band gap of BiFeO3 originating from the ferroelectric photovoltaic effect. These results demonstrate that hydrothermal and microwave-assisted hydrothermal method are simple, inexpensive and rapid to grow high quality epitaxial BiFeO3 film with potential application in photoelectric detection and photovoltaic.

MICROPROCESSOR MEASURING SYSTEM FOR DYNAMICS AND ENERGY OF MOBILE MACHINES

The paper presents a synthesis of a microprocessor-based measuring system for the dynamics and energy of mobile machines. It was determined that the measuring systems used to study the operation of cars, tractors and machine-tractor units today are not able to measure many parameters of functioning in dynamics during the execution of technological processes in agriculture. The use of microprocessors changes the structure of the digital part of devices. Significant computing capabilities of microprocessors allow the use of more complex work algorithms. At the same time, the requirements for the analog part of the measuring device are reduced and high metrological and operational characteristics are ensured. Based on the microprocessor, a measuring system was created to determine the dynamic and traction-energy indicators of the functioning of mobile machines. The main element of this system is a computing module consisting of an STM32F407 microprocessor computing element that processes data from sensors and a microprocessor element for data collection and storage. A hard disk, solid-state drive or USB Flash drive is used as an information storage device. The computing module has a touch display for displaying parameters and controlling the measuring system, so it can be used without an external personal computer. The number and types of sensors with which the machine is equipped during testing depends on its type and parameters required for study. To determine the dynamics of the tractor or unit elements, an inertial measuring device is used, consisting of gyroscopes and acceleration sensors, the number of which depends on the number of tested elements. The measuring system of dynamic and energy parameters of tractors and machine-tractor units was used in the study of the KhTZ-242T wheeled tractor. The dependence of the traction force of the seeder and the spectral density was determined. The results of experimental studies proved the effectiveness of using a microprocessor measuring system during field and laboratory tests of tractors and machine-tractor units. Keywords: microprocessor, measuring system, tractor, experimental studies.

Valley polarization of trions in monolayer MoSe2 interfaced with bismuth iron garnet

Interfacing atomically thin van der Waals semiconductors with magnetic substrates enables additional control on their intrinsic valley degree of freedom and provides a promising platform for the development of novel valleytronic devices for information processing and storage. Here we study circularly polarized photoluminescence in heterostructures of monolayer MoSe2 and thin films of ferrimagnetic bismuth iron garnet (BIG). We observe strong emission from charged excitons with circular polarization opposite to that of the pump and demonstrate contrasting response to left and right circularly polarized excitation, associated with finite out-of-plane magnetization in the substrate. We propose a theoretical model accounting for magnetization-induced imbalance of charge carriers in the two valleys of MoSe2, as well as for valley-switching scattering from B to A excitons and fast formation of trions with extended valley relaxation times, which shows excellent agreement with the experimental data. Our results establish monolayer MoSe2 interfaced with BIG as a promising system for valley control of charged excitons.

Exchange Coupling in Synthetic Anion‐Engineered Chromia Heterostructures

AbstractControl of magnetic states by external factors has garnered a mainstream status in spintronic research for designing low power consumption and fast‐response information storage and processing devices. Previously, magnetic‐cation substitution was the conventional approach to induce ferromagnetism in an intrinsic antiferromagnet. Theoretically, anion doping is proposed to be another means to change magnetic ground states. Here, the authors demonstrate the synthesis of high‐quality single‐phase chromium oxynitride thin films using in‐situ nitrogen doping. Unlike antiferromagnetic monoanionic chromium oxide and nitride phases, chromium oxynitride exhibits a robust ferromagnetic and insulating state, as demonstrated by the combination of multiple magnetization probes and theoretical calculations. With increasing the nitrogen content, the crystal structure of chromium oxynitride transits from trigonal (Rc) to tetragonal (4 mm) phase and its saturation magnetization reduces significantly. Furthermore, they achieve a large and controllable exchange bias field in the chromia heterostructures by synthetic anion engineering. This work reflects the anion engineering in functional oxides towards potential applications in giant magnetoresistance and tunnelling junctions of modern magnetic sensors and read heads.

Sign reversal of unidirectional magnetoresistance in monocrystalline Fe/Pt bilayers

The discovery of unidirectional magnetoresistance (UMR) in ferromagnet/heavy metal heterostructures provides one possibility to detect the magnetization direction with a simple two-terminal geometry. We investigated the temperature and thickness dependence of UMR in single-crystalline Fe/Pt bilayers and discovered an obvious sign reversal when increasing the Fe thickness at low temperature. Meanwhile, the same phenomenon is observed when increasing temperature for thick Fe samples. All the UMR mechanisms are quantitatively analyzed and the UMR contribution induced by the thermal effect shows a thickness-dependent sign change, thus the sign reversal of UMR is attributed to the competition between the contributions on UMR from the thermal effect and the spin accumulation induced by the spin Hall effect in the Pt layer. Our results emphasize the thermal contribution to the UMR in ferromagnet/heavy metal heterostructures and suggest a promising way to tune the UMR, which will promote its application in information storage devices.

Robust formation of skyrmion and skyrmionium in magnetic hemispherical shells and their dynamic switching

We explored the variations of the topological magnetic textures of vortices, skyrmions, and skyrmioniums in magnetic elements of hemispherical-shell shape with respect to surface-normal uniaxial magnetic anisotropy constant ${K}_{u}$, Dzyaloshinskii-Moriya interaction (DMI) constant ${D}_{\mathrm{int}}$, and shell diameter $2R$. For given values of $2R$, the combination of ${K}_{u}$ and ${D}_{\mathrm{int}}$ plays a crucial role in the stabilization of those different spin textures. With decreasing $2R$, the geometrical confinement of hemispherical shells more significantly affects the stabilization of skyrmions owing to curvature-induced DM-like interaction. This effect is contrastingly dependent on the sign of ${D}_{\mathrm{int}}$: skyrmion formation is more favorable for positive ${D}_{\mathrm{int}}$ values, whereas it is less favorable for negative ones. A quite promising feature is that skyrmions can be stabilized even in the absence of intrinsic DMI for $2R<25\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$. We also explored characteristic dynamic properties of skyrmions excited by in-plane and out-of-plane oscillating magnetic fields. Similarly to the fundamental dynamic modes found in planar dots, in-plane gyration and azimuthal spin-wave modes as well as out-of-plane breathing modes were found, but additional higher-frequency hybrid modes also appeared due to coupling between radially quantized and azimuthal spin-wave modes. Finally, we found a switching behavior of skyrmion polarity through a transient skyrmionium state using very-low-strength AC magnetic fields. This work provides further physical insight into the static and dynamic properties of skyrmions in curved-geometry nanodots and suggests potential applications to low-power-consumption and ultra-high-density information-storage devices.

Proton Transport in Hydrated GdOx Measured with GdCo Magnetic Sensing Layer

Solid state ionic materials such as metal oxide ceramics are of interest due to the wide variety of properties that can be controlled through voltage control of ion concentration and transport in these materials, e.g. electrical resistivity, optical properties, and magnetic properties. Ion movement through a solid oxide electrolyte film can be controlled very simply by electrical gating of the oxide, i.e. applying a voltage across the film. The ease of processing and CMOS compatibility of metal oxides makes them strong candidate materials for next-generation devices for information storage and computing, sensing, energy generation (fuel cells), and energy storage (batteries).Hydrogen ions (protons) take the form of (OH)O • defects in oxides and move by hopping between oxygen sites (Grotthuss mechanism); their small size allows for high conductivity.8 Protonic conduction in oxides has been studied in solid oxide fuel cells (SOFCs)1; proton incorporation has also been shown to change the optical4, electrical2,3, and magnetic properties of the oxide5, or a combination of multiple properties e.g. through inducing phase changes in strontium cobalt oxide (SCO)6. However, current work focuses on materials that require high-temperature processing and operation (>200C, or up to 600-1000C for SOFCs), and bulk or microscale films. This work aims to take solid oxide protonic devices down to the ultrathin (10-100nm) scale, to introduce simpler fabrication techniques (sputtering), and to achieve room-temperature operation of ionic devices. We investigate gadolinium oxide (GdOx) as a model material due to its hygroscopic nature, which allows for fast room-temperature proton conduction.7,8 Using variations of a Pt/Co/GdOx/Au device structure, a gate voltage of 2-5V is applied, initiating a hydrolysis reaction at the top electrode and allowing water to be incorporated into the film. The electric field within the GdOx drives protons to the bottom interface, where it can diffuse into the adjacent magnetic layer and affect a variety of properties. Thin film ferromagnetic materials such as cobalt have been shown to undergo dramatic changes in their magnetic anisotropy with voltage gating, due to the incorporation and removal of hydrogen at the interface with the electrolyte and within the magnetic layer.6 Control of the compensation temperature of a thin film ferrimagnet and control of exchange bias in an antiferromagnet have also been demonstrated with this magneto-ionic proton pump mechanism.9,10 Using a gadolinium cobalt (GdCo) magnetic layer inserted into the MOM device stack to detect the presence of hydrogen, we have developed a sensor for use in a novel time-domain proton transport measurement. We apply short voltage pulses to the device and use magneto-optic Kerr effect (MOKE) to observe the resulting changes in the compensation temperature and magnetic state of the sensor layer. This can be used as a more direct measure of the presence of protons at the bottom interface, as compared to frequency domain measurements such as electrochemical impedance spectroscopy (EIS). We also show that humidity affects the proton transport in the oxide layer, using neutron and x-ray reflectometry to observe the growth of a gadolinium hydroxide (Gd(OH)3) layer with high hydrogen concentration upon exposing the film to a high humidity environment.11 References Q. Minh, M. B. Mogensen. Reversible Solid Oxide Fuel Cell Technology for Green Fuel and Power Production. Electrochem. Soc. Interface, 55–62 (2013).Huang et al. Three-terminal resistive switch based on metal/metal oxide redox reactions, Scientific Reports, 7 (2017).Messerschmitt, F. Kubicek, M., Rupp, J. L. M. How Does Moisture Affect the Physical Property of Memristance for Anionic–Electronic Resistive Switching Memories?, Advanced Functional Materials, 25, 5117-5125 (2015).Huang, M., Jun Tan, A., Büttner, F. et al. Voltage-gated optics and plasmonics enabled by solid-state proton pumping. Nat Commun 10, 5030 (2019).Tan et al. Magneto-ionic control of magnetism using a solid-state proton pump, Nature Materials, 17 (2018).Lu, N. et al. Electric-field control of tri-state phase transformation with a selective dual-ion switch, Nature 546, 124–128, (2017)Norbya, T. Proton conduction in oxides, Solid State lonics, 40/41, 857-862 (1990).Larring and Norby. Protons in rare earth oxides, Solid State Ionics, 77 (1995).Huang, M., Hasan, M.U., Klyukin, K. et al. Voltage control of ferrimagnetic order and voltage-assisted writing of ferrimagnetic spin textures. Nanotechnol. 16, 981–988 (2021).Zehner, J. et al. Magnetoionic control of perpendicular exchange bias. Phys. Rev. Materials 5, L061401 (2021).Tan, A.J., Huang, M., Sheffels, S., et al. Hydration of gadolinium oxide (GdOx) and its effect on voltage-induced Co oxidation in a Pt/Co/GdOx/Au heterostructure. Phys. Rev. Materials 3, 064408 (2019). Figure 1

Magnetic coupling engineering-induced excellent spin transport in covalently linked nanographene dimers

A generally accepted viewpoint is that molecules with a spin S = 1/2 did not show any magnetic coupling when assembled into molecular dimers. However, a recent experiment successfully synthesizes covalently linked five-membered ring decorated nanographene dimers that are antiferromagnetically coupled with each other [Phys. Rev. Lett. 124 (2020) 147206]. Motivated by this work, we further study the effect of magnetic coupling engineering on spin transport properties in covalently linked nanographene dimers-based molecular devices. Our results show that excellent spin transport properties are strongly dependent on the magnetic coupling strength of the covalently linked five-membered ring decorated nanographenes. A variety of interesting spin transport properties are found, including “inverse Schottky” characteristic, high spin polarization, reverse of spin polarization, and large magnetoresistance. These results indicate that the covalently linked five-membered ring decorated nanographene dimers can be designed as over-current protection devices, and information storage and logic devices by engineering of magnetic coupling. Our works confirm an efficient way for building high-performance carbon-based molecular spintronic devices.

Light-triggered reversible supramolecular self-assembly of azo groups-functionalized copper nanoclusters

Metal nanoclusters (NCs) have attracted much attention due to their ultrasmall sizes and unique electronic structures. In recent years, the light-induced reversible assembly of Au NCs is already reported. However, to achieve light-triggered reversible self-assembly of Cu NCs is still challenging. Herein, we prepared photoresponsive Cu NCs by using an azo-containing ligand, i.e., 3,5-dimethyl-4-(phenyldiazenyl)-1H-pyrazole) (abbreviated to Hazopz). Each nanocluster contains three Cu(I) in the core and has atomic precision (denoted as Cu3-NCs hereafter). Self-assembly of Cu3-NCs into nanofibers occurred in binary solvent mixture with toluene as a good solvent and methanol (MeOH) as a poor one. When the suspension containing the nanofibers was irradiated by UV light, the originally straight nanofibers became bent. This morphological change is mainly due to the isomerization of the peripheral azo groups of the Cu3-NCs from trans- to cis-conformation, and to a small extent ascribed to the increased solubility of the cis-conformation of the azo groups in the binary solvent. The disassembled aggregates can reassemble and the bent nanofibers can become straight again when exposed to visible light. This process can be repeated for at least three times, indicating the high reversibility of this light-triggered morphological change of Cu3-NCs. The one-dimensional self-assemblies with light-triggered, reversible morphological changes achieved in this work can be potentially used as a medium material in an optical information storage device, and can write and erase information through the irradiation of UV light and visible light.