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Ferromagnetic insulator plays a pivotal role in various emerging spintronic effects and can be integrated as an essential component into future spintronic devices. However, ferromagnetic insulating perovskite oxides are rather scarce due to the strong coupling between ferromagnetism and metallicity via double exchange and superexchange mechanisms, severely restricting the development for oxide-based spintronic devices. Here, the disorder of manganite La2/3Sr1/3MnO3 (LSMO) films grown on MgAl2O4 substrates is utilized to decouple ferromagnetism and metallicity, thereby inducing a ferromagnetic insulating state over a rather broad temperature and thickness range. These films are non-crystalline with enormous disorder. The films with thicknesses less than 16 nm are in completely insulating state, and the films with thicknesses larger than 16 nm are in essentially insulating state with high resistivity. This insulating state is ascribed to the disorder in LSMO films and can be fitted by a localization model. In contrast, all LSMO films exhibit ferromagnetic transitions with considerable saturated magnetic moments and the Curie temperatures near room temperature, leading to the ferromagnetic insulator phase in our manganite heterostructures over a large temperature and thickness interval. Our results broaden the mind for inducing new ferromagnetic insulating state for potential applications in spintronic devices.

Excellent magnetoresistive materials have attracted people's attention due to their wide applications. Unfortunately, few cobalt-based perovskite oxides can demonstrate good magnetoresistance (MR) properties. Herein, a new series of SrCo1-xFexO2.9-δF0.1 (x = 0, 0.1, 0.2, and 0.3) perovskites are prepared and studied as potential magnetoresistive materials. Room temperature X-ray diffraction (XRD) and Rietveld refinement confirm the simple cubic structure of all samples. The magnetization vs temperature measurement reveals that the magnetic transition temperature goes down with the increase of Fe content, suggesting the weakened ferromagnetism caused by Fe4+-O-Co3+, Fe3+-O-Fe3+ and Fe4+-O-Fe4+ interactions. And the resistivity data of all Fe doped samples can be better fitted using Mott's variable range hopping (VRH) model, suggesting its disordering semi-conduction behavior. Astonishingly, the SrCo0.8Fe0.2O2.9-δF0.1 ceramic sample owns the giant negative magnetoresistance value of approximately 90% at 5 K in 90 kOe, which is almost the largest negative magnetoresistance in cobalt-based perovskite oxides, indicating that cobalt-based perovskites can be an underlying material system for the research of the potential material applying to magnetic sensors or other spintronic devices.

In this paper, we report the rational synthesis of stable γ-phase MnS1−xSex (0 ≤ x ≤ 0.45) nanoflakes. By tuning the parameters of synthesis duration and temperature, we produced a detailed growth phase diagram.

A high-quality perovskite film is critical to realize high-efficiency and hysteresis-less perovskite solar cells (PSCs). However, a solution-processed perovskite layer presents many ionic vacancies...

The oxygen reduction reaction is essential for fuel cells and metal-air batteries in renewable energy technologies. Developing platinum-group-metal (PGM)-free catalysts with comparable catalytic performance is highly desired for cost efficiency. Here, we report a tin (Sn) nanocluster confined catalyst for the electrochemical oxygen reduction. The catalyst was fabricated by confining 1-1.5 nm sized Sn nanoclusters

The topotactic connection style of oxygen octahedron/tetrahedron in transition metal oxides (TMOs) is an important feature that modulates their corresponding physical properties. Using a simple chemical doping technique, we obtained Sr1−xNdxCoO3-δ with a crystal structure transition from face-shared octahedron to corner-shared octahedron/tetrahedron. The Rietveld analyses of the X-ray diffraction (XRD) patterns show that the crystal structure changes from rhombohedral to cubic and the connection style transforms from face-shared to corner-shared with the increase neodymium (Nd) content. During this process, the ferromagnetic behavior is greatly improved due to the larger amount of the corner-shared cubic SrCoO3-δ phase. The synchrotron radiation X-ray absorption spectroscopies of the Co L-edge and O K-edge show that Nd-doping mainly affects the electronic structure of oxygen rather than the valence state of Co. Thereby, the Nd changes the connection style of oxygen octahedron/tetrahedron, which then alters the magnetic interactions.

Piezoelectric materials have recently demonstrated their potential applications in clean energy exploration and environmental remediation through triggering a number of catalytic reactions by harvesting waste vibrational energy in the environment. In this work, unique lead-free 0.7BiFeO3-0.3BaTiO3 (BF-BT) nanoparticles with tuned band structure were synthesized by the hydrothermal method for use as piezoelectric catalysts to generate hydrogen by splitting water; a high production rate of 1.322 mmol/g was achieved in 1 h, which is 10 times higher than the production rate of pure BiFeO3. Of particular interest, BF-BT particles attached to nickel mesh have the ability to degrade rhodamine B in flowing water, demonstrating their potential to treat polluted water by anchoring BF-BT in drains. Finally, we propose novel insight on the piezocatalytic mechanism, which is based on the internal electric field (the sum of the depolarization field and the screening charge field) that drives electron/hole separation and movement.

Bismuth layer-structured oxides with natural superlattices have attracted great attention because of their fascinating functional properties, such as ferroelectricity, ferromagnetism, multiferroici...

Stable and efficient photoelectrochemical water splitting has been achieved using a BaTaO2N photoanode decorated with CoO microflowers. The CoO microflowers effectively collect holes from BaTaO2N which kinetically protects BaTaO2N against photocorrosion. A Faraday efficiency of almost unity (99.2%) has been recorded for O2 evolution reactions. The tips of the CoO microflowers are the most active sites for water oxidation reactions.

Recent experiments on magic-angle twisted bi-layer graphene have attracted intensive attention due to exotic properties such as unconventional superconductivity and correlated insulation. These phenomena were often found at a magic angle less than 1.1°. However, the preparation of precisely controlled bi-layer graphene with a small magic angle is challenging. In this work, electronic properties of large-angle twisted bi-layer graphene (TBG) under pressure are investigated with density functional theory. We demonstrate that large-angle TBG can display flat bands nearby the Fermi level under pressure, which may also induce interesting properties such as superconductivity which have only been found in small-angle TBG at ambient pressure. The Fermi velocity is found to decrease monotonously with pressure for large twisted angles, e.g., 21.8°. Our work indicates that applying pressure provides opportunities for flat-band engineering in larger angle TBG and supports further exploration in related investigations.

Single atom catalysts (SACs) are of great importance for oxygen reduction, a critical process in renewable energy technologies. The catalytic performance of SACs largely depends on the structure of their active sites, but explorations of highly active structures for SAC active sites are still limited. Herein, we demonstrate a combined experimental and theoretical study of oxygen reduction catalysis on SACs, which incorporate M-N3 C1 site structure, composed of atomically dispersed transition metals (e.g., Fe, Co, and Cu) in nitrogenated carbon nanosheets. The resulting SACs with M-N3 C1 sites exhibited prominent oxygen reduction catalytic activities in both acidic and alkaline media, following the trend Fe-N3 C1 > Co-N3 C1 > Cu-N3 C1 . Theoretical calculations suggest the C atoms in these structures behave as collaborative adsorption sites to M atoms, thanks to interactions between the d/p orbitals of the M/C atoms in the M-N3 C1 sites, enabling dual site oxygen reduction.

The electrochemical performance of supercapacitors is suppressed by a large number of defects in the interface of heterostructure due to lattice mismatch. In this paper, the (001) oriented rutile M...

寻找一种性能良好的磁性绝缘材料是发展新型多功能量子自旋电子器件至关重要的基础, 但是大多数已知的磁性绝缘材料具有居里温度低( 300 K), 铁磁性和结构对称性差的特点. 本工作中, 我们成功设计并制备了一种新型的磁性绝缘体: Bi8Fe2.8Co0.2-Ti2O20Cl, 它具有包含五层钙钛矿层的层状Sillen-Aurivillius结构. 令人惊讶的是, 此种化合物的居里温度达到了约 804 K, 比未掺杂的奈耳温度提高超过 300 K. 此外, 由于Sillen层的存在, Bi8Fe2.8-Co0.2Ti2O20Cl具有比所有已知相同Co摩尔比掺杂的Aurivillius氧化物更大的剩余磁化强度. X射线吸收光谱(XAS)和X-光磁性圆二色性(XMCD)光谱分析表明, Bi8Fe2.8Co0.2Ti2O20Cl的铁磁性主要是由Co掺杂引起的FeO6八面体的形变和Fe−O−Co的Dzyaloshinskii-Moriya(D-M)相互作用所致.

Antiferromagnets have attracted considerable interest in the field of spintronics due to their attractive characteristics such as ultrafast spin dynamics and robustness against external magnetic field perturbations. Sr2IrO4 is a rare example of antiferromagnetic semiconductor oxide and has been extensively studied in anisotropic magnetoresistance-based spintronics. However, the anisotropic magnetoresistance of Sr2IrO4 films is usually very small. Herein, we have prepared a (Sr2IrO4)4/(La2/3Sr1/3MnO3)5 superlattice which shows an enhanced anisotropic magnetoresistance compared to Sr2IrO4 film or La2/3Sr1/3MnO3/Sr2IrO4 heterostructure and an obvious nonvolatile memory effect that is comparable to Sr2IrO4 single crystals. Through magnetic measurements, the increased coercivity and the exchange bias at low temperatures reveal the interfacial magnetic coupling between Sr2IrO4 and La2/3Sr1/3MnO3. Additionally, the remarkable anisotropic magnetoresistance and clear hysteresis of anisotropic magnetoresistance with distinct fourfold symmetry can be controlled by temperature and magnetic field. These findings demonstrate that the superlattices of heavy transition metal oxide Sr2IrO4 are excellent platforms for antiferromagnetic spintronics.

Lattice-oxygen-active (Bi0.5Co0.5)2O3 was successfully prepared through vacancy modulation and demonstrated great OER activity and performance.

The efficient adsorption of molecules on functional material surfaces plays a crucial role in promoting their performances in various applications. In contrast with the common route to improve molecule adsorption by simply increasing the specific surface area, a new and more effective strategy to enhance adsorption on ferroelectric Bi3TiNbO9 based on the ferroelectric external screening effect was explored in this work. Single-crystal nanosheets were synthesized by the molten salt method (BTNO-M). Benefitting from the ferroelectric external screening effect, the specific-surface-area-normalized adsorption amounts of rhodamine B (cationic dye) and methyl orange (anionic dye) on BTNO-M were 22.3 and 10.7 times higher than those on P25, respectively. The enhanced adsorption induced by the ferroelectric external screening effect was further demonstrated by corona-poling experiments. Correspondingly, the direct photoexcitation degradation rates of rhodamine B and methyl orange (λ = 254 nm) by BTNO-M were 6.91 and 7.54 times those for P25. More importantly, the indirect photosensitization degradation rate of rhodamine B (λ > 420 nm) by BTNO-M was 13.6 times as high as that for P25, demonstrating that efficient adsorption greatly accelerated the photocatalytic process. This new strategy may also have potential applications in dye-sensitized solar cells, photoelectrochemical cells, chemosensors or biosensors.

Rationally designing bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with high activity and long term stability remains to be a big challenge. Herein, we report in situ synthesized uniform Ru-doped FeCoP (FeCoRuP) nanoarrays as a bifunctional electrocatalyst for highly efficient overall water splitting. The introduction of Ru modifies the electronic interaction between cation active sites due to the electronegativity difference, which also introduces more active sites by creating lattice defects and distortion. Benefiting from the rich active sites and the strong electronic interaction, the optimized Ru-doped FeCoP exhibits excellent HER activities (45 mV at 10 mA cm−2) and OER activity (214 mV at 20 mA cm−2), together with excellent long-term durability (110 h) in alkaline media. An overall water splitting cell in which both anode and cathode are composed of the FeCoRuP catalyst exhibits an ultralow voltage of 1.47 V at 10 mA cm−2, which is superior to the benchmark 20% Pt/C‖IrO2 electrodes (1.68 V at 10 mA cm−2). The present work offers a simple but effective approach to promote the overall water splitting performance of transition metal phosphides by modulating the electronic structure of active sites.

Co-catalysts such as precious metals are usually necessary to promote the photocatalytic generation of hydrogen from water through inhibiting the recombination of photo-generated carriers. However, precious metals are expensive and harmful to the environment. In this work, an ethylene glycol (EG) molecule, which was chemically anchored on SrTiO3 nanoparticles (EG@STO) via an in situ process, was used as a co-catalyst for the first time. The first-principles calculation shows that the EG molecule chemically anchored on SrTiO3 is beneficial for the directional migration of carriers and accelerates the hydrogen evolution reaction. A photocatalytic hydrogen generation efficiency of 237 μmol g−1 h−1 was achieved with EG@STO, which is 19.5 times higher compared to that of SrTiO3. Moreover, EG@STO remained stable after 32 hours of reaction; in other words, the EG molecule is designed as a new type of efficient and stable co-catalyst, which provides an alternative approach for better semiconductor photocatalytic hydrogen reduction.

Effective control of magnetic anisotropy, including perpendicular magnetic anisotropy (PMA) and lateral magnetic anisotropy, is important for the design of low-power and high-density spintronic devices. However, the rarity of oxide materials with PMA and stringent conditions required to control magnetic anisotropy have prevented its large-scale application. Here, we demonstrate that the magnetic anisotropy of SrRuO3 films can be specified on-demand by adjusting the content of Ru vacancies to control the structure of the films. With the increase in Ru vacancies, the structure of SrRuO3 changes from orthorhombic to tetragonal. The field angle dependence of the Hall resistance confirmed that the uniaxial magnetic easy axis of SrRuO3 thin films continuously rotates in the (100)pc crystallographic plane, which is identical to the continuous phase transition. Our results not only provide a way to continuously tune the physical properties of epitaxial oxide films by continuously changing the composition but also help to provide guidance for the on-demand design of spintronic devices.

The magnetoresistance (MR) of spin values usually displays a symmetric dependence on the magnetic field. An antisymmetric MR phenomenon has been discovered recently that breaks the field symmetry and has the potential to realize multi-bit memory. In this work, we report a controllable switch between the antisymmetric and symmetric MRs and propose a multi-bit memory performance in Fe3GeTe2 (FGT)/graphite/FGT trilayer with modified vertical geometry. Via investigating the evolution of the antisymmetric MR depending on the spatial distribution, current direction, and magnetization configuration, we demonstrate that the antisymmetric MR results from the local nonequilibrium current through the trilayer. Furthermore, an exchange bias effect is induced which modifies the antisymmetric MR. A stable multi-bit memory is presented in the heterostructure. Such architecture for multi-state memory provides insights into other spin-valve structures to improve storage density.