Duplex Interpenetrating-Phase FeNiZn and FeNi_(3)Heterostructure with Low-Gibbs Free Energy Interface Coupling for Highly Efficient Overall Water Splitting

The sluggish kinetics of both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)generate the large overpotential in water electrolysis and thus high-cost hydrogen production.Here,multidimensional nanoporous interpenetrating-phase FeNiZn alloy and FeNi_(3)intermetallic heterostructure is in situ constructed on NiFe foam(FeNiZn/FeNi_(3)@NiFe)by dealloying protocol.Coupling with the eminent synergism among specific constituents and the highly efficient mass transport from integrated porous backbone,FeNiZn/FeNi_(3)@NiFe depicts exceptional bifunctional activities for water splitting with extremely low overpotentials toward OER and HER(η_(1000)=367/245 mV)as well as the robust durability during the 400 h testing in alkaline solution.The as-built water electrolyzer with FeNiZn/FeNi_(3)@NiFe as both anode and cathode exhibits record-high performances for sustainable hydrogen output in terms of much lower cell voltage of 1.759 and 1.919 V to deliver the current density of 500 and 1000 mA cm^(-2)as well long working lives.Density functional theory calculations disclose that the interface interaction between FeNiZn alloy and FeNi_(3)intermetallic generates the modulated electron structure state and optimized intermediate chemisorption,thus diminishing the energy barriers for hydrogen production in water splitting.With the merits of fine performances,scalable fabrication,and low cost,FeNiZn/FeNi_(3)@NiFe holds prospective application potential as the bifunctional electrocatalyst for water splitting.

Prediction of one-dimensional CrN nanostructure as a promising ferromagnetic half-metal

Searching for one-dimensional(1D)nanostructure with ferromagnetic(FM)half-metallicity is of significance for the development of miniature spintronic devices.Here,based on the first-principles calculations,we propose that the 1D CrN nanostructure is a FM half-metal,which can generate the fully spin-polarized current.The ab initio molecular dynamic simulation and the phonon spectrum calculation demonstrate that the 1D CrN nanostructure is thermodynamically stable.The partially occupied Cr-d orbitals endow the nanostructure with FM half-metallicity,in which the half-metallic gap(?s)reaches up to 1.58 eV.The ferromagnetism in the nanostructure is attributed to the superexchange interaction between the magnetic Cr atoms,and a sizable magnetocrystalline anisotropy energy(MAE)is obtained.Moreover,the transverse stretching of nanostructure can effectively modulate?s and MAE,accompanied by the preservation of half-metallicity.A nanocable is designed by encapsulating the CrN nanostructure with a BN nanotube,and the intriguing magnetic and electronic properties of the nanostructure are retained.These novel characteristics render the 1D CrN nanostructure as a compelling candidate for exploiting high-performance spintronic devices.

The predicaments and expectations in development of magnetic semiconductors

Over the past half a century, considerable research activities have been directing towards the development of magnetic semiconductors that can work at room temperature. These efforts were aimed at seeking room temperature magnetic semiconductors with strong and controllable s, p-d exchange interaction. With this s, p-d exchange interaction, one can utilize the spin degree of freedom to design applicable spintronics devices with very attractive functions that are not available in conventional semiconductors. Here, we first review the progress in understanding of this particular material and the dilemma to prepare a room temperature magnetic semiconductor. Then we discuss recent experimental progresses to pursue strong s, p-d interaction to realize room temperature magnetic semiconductors, which are achieved by introducing a very high concentration of magnetic atoms by means of low-temperature nonequilibrium growth.

Janus VXY monolayers with tunable large Berry curvature

The Rashba effect and valley polarization provide a novel paradigm in quantum information technology. However,practical materials are scarce. Here, we found a new class of Janus monolayers VXY(X = Cl, Br, I;Y = Se, Te) with excellent valley polarization effect. In particular, Janus VBrSe shows Zeeman type spin splitting of 14 meV, large Berry curvature of 182.73 bohr2,and, at the same time, a large Rashba parameter of 176.89 meV·?. We use the k·p theory to analyze the relationship between the lattice constant and the curvature of the Berry. The Berry curvature can be adjusted by changing the lattice parameter,which will greatly improve the transverse velocities of carriers and promote the efficiency of the valley Hall device. By applying biaxial strain onto VBrSe, we can see that there is a correlation between Berry curvature and lattice constant, which further validates the above theory. All these results provide tantalizing opportunities for efficient spintronics and valleytronics.

Magnetic tuning in a novel half-metallic Ir_(2)TeI_(2) monolayer

A two-dimensional(2D) high-temperature ferromagnetic half-metal whose magnetic and electronic properties can be flexibly tuned is required for the application of new spintronics devices. In this paper, we predict a stable Ir_(2)TeI_(2) monolayer with half-metallicity by systematical first-principles calculations. Its ground state is found to exhibit inherent ferromagnetism and strong out-of-plane magnetic anisotropy of up to 1.024 meV per unit cell. The Curie temperature is estimated to be 293 K based on Monte Carlo simulation. Interestingly, a switch of magnetic axis between in-plane and out-of-plane is achievable under hole and electron doping, which allows for the effective control of spin injection/detection in such 2D systems. Furthermore, the employment of biaxial strain can realize the transition between ferromagnetic and antiferromagnetic states. These findings not only broaden the scope of 2D half-metal materials but they also provide an ideal platform for future applications of multifunctional spintronic devices.

Thermodynamic criterion for searching high mobility two-dimensional electron gas at KTaO_(3)interface

Two-dimensional electron gases(2 DEGs)formed at the interface between two oxide insulators present a promising platform for the exploration of emergent phenomena.While most of the previous works focused on SrTiO_(3-)based 2 DEGs,here we took the amorphous-ABO_(3)/KTaO_(3)system as the research object to study the relationship between the interface conductivity and the redox property of B-site metal in the amorphous film.The criterion of oxide-oxide interface redox reactions for the B-site metals,Zr,Al,Ti,Ta,and Nb in conductive interfaces was revealed:the formation heat of metal oxide,ⅢH_(f)^(o),is lower than-350 kJ/(mol O)and the work function of the metalΦis in the range of 3.75 eV<Φ<4.4 eV.Furthermore,we found that the smaller absolute value ofⅢH_(f)^(o)and the larger value ofΦof the B-site metal would result in higher mobility of the two-dimensional electron gas that formed at the corresponding amorphous-ABO_(3)/KTaO_(3)interface.This finding paves the way for the design of high-mobility all-oxide electronic devices.

Probing the magnetization switching with in-plane magnetic anisotropy through field-modified magnetoresistance measurement

Effective probing current-induced magnetization switching is highly required in the study of emerging spin-orbit torque(SOT)effect.However,the measurement of in-plane magnetization switching typically relies on the giant/tunneling magnetoresistance measurement in a spin valve structure calling for complicated fabrication process,or the non-electric approach of Kerr imaging technique.Here,we present a reliable and convenient method to electrically probe the SOT-induced in-plane magnetization switching in a simple Hall bar device through analyzing the MR signal modified by a magnetic field.In this case,the symmetry of MR is broken,resulting in a resistance difference for opposite magnetization orientations.Moreover,the feasibility of our method is widely evidenced in heavy metal/ferromagnet(Pt/Ni_(20)Fe_(80) and W/Co_(20)Fe_(60)B_(20))and the topological insulator/ferromagnet(Bi_(2)Se_(3)/Ni_(20)Fe_(80)).Our work simplifies the characterization process of the in-plane magnetization switching,which can promote the development of SOT-based devices.

Manipulating non-collinear antiferromagnetic order and thermal expansion behaviors in triangular lattice Mn_(3)Ag_(1-x)Sn(Ge)_(x)N

Magnetic materials with non-collinear spin orderings provide an outstanding platform to probe spin-tronic phenomena owing to their strong spin-orbit coupling(SOC)and unique Berry phase.It is thus important to obtain a non-collinear antiferromagnetic(AFM)phase at room temperature(RT).Signifi-cantly,the discovery of novel materials with nearly zero thermal expansion(ZTE)property near RT is required and pursued for avoiding thermal stress and fracture in spintronic devices.Herein,the doping of Sn(Ge)at the Ag site in the triangular lattice Mn_(3)Ag_(1-x)Sn(Ge)_(x)N compounds increases effectively the Neel point and makes the interesting non-collinearГ^(5g)AFM phase exist above RT.The magnetic phase diagrams withГ^(5g)phase up to 498 K were built by the combined analysis of neutron powder diffraction(NPD),magnetic measurements,electronic transport,and differential scanning calorimetry(DSC).The thermal expansion behaviors of Mn_(3)Ag_(1-x)Sn(Ge)_(x)N were modulated,and the nearly ZTE above RT was achieved in Mn_(3)Ag_(0.5)Ge_(0.5)N withinГ^(5g)AFM ordering.Our findings offer an effective way to tailor the non-collinear AFM ordering and correlated thermal expansion behavior for potential use in the emerging field of thermal stress-free magnetic chip materials.

Two-dimensional rectangular bismuth bilayer:A novel dual topological insulator

Dual topological insulator(DTI),which simultaneously hosts topological insulator(TI)and topological crystalline insulator(TCI)phases,has attracted extensive attention since it has a better robustness of topological nature and broad application prospects in spintronics.However,the realization of DTI phase in two-dimensional(2D)system is extremely scarce.By first-principles calculations,we predict that the 2D rectangular bismuth(R–Bi)bilayer is a novel DTI,featured by topological invariant=1,mirror Chern number C_(M)=–1,and metallic edge states within the bulk band gap.More interestingly,the TCI phase in bilayer is protected by horizontal glide mirror symmetries,rather than the usual mirror symmetry.The bulk band gap can be effectively tuned by vertical electric field and strain.Besides,the electric field can trigger the transition between TI and metallic phases for the bilayer,accompanied by the annihilation of TCI phase.On this basis,a topological field effect transistor is proposed,which can rapidly manipulate spin and charge carriers via electric field.The KBr(110)surface is demonstrated as an ideal substrate for the deposition of bilayer.These findings provide not only a new strategy for exploiting 2D DTI,but also a promising candidate for spintronic applications.

Ultrathin SrTiO_(3)-based oxide memristor with both drift and diffusive dynamics as versatile synaptic emulators for neuromorphic computing

Artificial synapses are electronic devices that simulate important functions of biological synapses,and therefore are the basic components of artificial neural morphological networks for brain-like computing.One of the most important objectives for developing artificial synapses is to simulate the characteristics of biological synapses as much as possible,especially their self-adaptive ability to external stimuli.Here,we have successfully developed an artificial synapse with multiple synaptic functions and highly adaptive characteristics based on a simple SrTiO_(3)/Nb:SrTiO_(3)heterojunction type memristor.Diverse functions of synaptic learning,such as short-term/long-term plasticity(STP/LTP),transition from STP to LTP,learning–forgetting–relearning behaviors,associative learning and dynamic filtering,are all bio-realistically implemented in a single device.The remarkable synaptic performance is attributed to the fascinating inherent dynamics of oxygen vacancy drift and diffusion,which give rise to the coexistence of volatile-and nonvolatile-type resistive switching.This work reports a multi-functional synaptic emulator with advanced computing capability based on a simple heterostructure,showing great application potential for a compact and low-power neuromorphic computing system.

Environmentally regulated intrinsic oxygen-ion transport for oxideion conductors

Oxide-ion conductors have been widely used as catalytic,conductive,detecting and other materials under oxidizing,reducing,inert,mixed environments and the like.However,so far the evaluation of their oxygen-ion transport(such as oxide-ion conductivity and oxygen permeability)either is extrinsic or is limited only in oxidizing or inert environment.Herein,the evaluation of intrinsic oxygen-ion transport for oxide-ion conductors in all environments seems especially important.In this work,a new test system was designed to enable the oxide-ion conductors placing in single oxidizing,reducing,inert or mixed environment separately,which also realized all the oxygen-vacancy concentrations of oxide-ion conductors are in equilibrium in all environments.The intrinsic oxide-ion conductivity and oxygen permeability were evaluated in all environments,and the influencing factors regulated by environments also were analyzed to correlate the variation of oxygen-ion transport.

Exploitable magnetic anisotropy and half-metallicity controls in multiferroic van der Waals heterostructure

Two-dimensional(2D)XY ferromagnets have drawn pronounced interest in recent years,but the characteristic of easy-plane magnetization restricts their application in spintronics to some extent.Here,we propose a general strategy for constructing multiferroic van der Waals heterostructures,aiming to achieve electrical control over the magnetic anisotropy in 2D XY ferromagnets.The validity of this strategy is verified by the heterostructure composed of ferromagnetic VBi_(2)Te_(4) and ferroelectric In_(2)Se_(3) monolayers.By manipulating the polarized states of In_(2)Se_(3),the VBi_(2)Te_(4) can be reversibly transformed between 2D XY and Heisenberg ferromagnets,characterized by the switching of easy magnetization axis between in-plane and out-of-plane directions.More interestingly,accompanied by the changes in magnetic anisotropy,the VBi_(2)Te_(4) also demonstrates a phase transition from a semiconductor to a half-metal state,which can be ascribed to the band alignment and interfacial charge transfer.The switchable magnetic and electronic properties enable the heterostructure to be utilized in nonvolatile memory and logic devices.Additionally,the half-metallicity and magnetocrystalline anisotropy energy of the heterostructure can be effectively tuned by biaxial strain.These findings not only pave the way for electrically nonvolatile control of 2D XY ferromagnet,but also facilitate the development of interfacial magnetoelectric physics and applications.

Synergistic coupling of NiFeZn-OH nanosheet network arrays on a hierarchical porous NiZn/Ni heterostructure for highly efficient water splitting

Efficient and economical electrocatalysts should be developed for oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)to split water for an extensive application prospect of green and clean hydrogen energy.Here,we develop highly efficient OER and HER electrocatalysts through the scalable fabrication of Ni Fe Zn hydroxide nanosheets firmly arrayed on a hierarchical porous intermetallic Ni Zn and Ni heterojunction over nickel foam(Ni Fe Zn-OH/Ni Zn-Ni/NF).One bimodal porous Ni Zn intermetallic/Ni layer is in situ constructed on the nickel foam surface to maximize the exposure of catalytic sites and build firm Ni Fe Zn-OH nanosheets via the redox reaction with Fe Cl;.Ni Fe Zn-OH/Ni Zn-Ni/NF shows low overpotentials of?50/600 around 235/284 m V for OER and?50/600 around73/212 m V for HER,small Tafel slopes of 46.1 and41.1 m V dec^(-1),and prolonged catalytic durability in an alkaline medium because of the strong synergistic effects of Zn doping,multiple interface engineering,and integral threedimensional free-standing scaffold.As bifunctional catalysts,Ni Fe Zn-OH/Ni Zn-Ni/NF required a low electrolytic voltage of1.49 V at 20 m A cm^(-2)(1.61 V at 100 m A cm^(-2))with a sustained and stable output for 40 h during water splitting.This work might provide insights into the exploration of low-cost and highly efficient intermetallic/multimetallic hydroxide heterostructured electrocatalysts for practical overall water splitting.

Switchable half-metallicity in A-type antiferromagnetic NiI_(2)bilayer coupled with ferroelectric In_(2)Se_(3)

Electrically controlled half-metallicity in antiferromagnets is of great significance for both fundamental research and practical application.Here,by constructing van der Waals heterostructures composed of two-dimensional(2D)A-type antiferromagnetic NiI_(2)bilayer(bi-NiI_(2))and ferroelectric In_(2)Se_(3)with different thickness,we propose that the half-metallicity is realizable and switchable in the bi-NiI_(2)proximate to In_(2)Se_(3)bilayer(bi-In_(2)Se_(3)).The polarization flipping of the bi-In_(2)Se_(3)successfully drives transition between half-metal and semiconductor for the bi-NiI_(2).This intriguing phenomenon is attributed to the joint effect of polarization field-induced energy band shift and interfacial charge transfer.Besides,the easy magnetization axis of the bi-NiI_(2)is also dependent on the polarization direction of the bi-In_(2)Se_(3).The half-metallicity and magnetic anisotropy energy of the bi-NiI_(2)in heterostructure can be effectively manipulated by strain.These findings provide not only a feasible strategy to achieve and control half-metallicity in 2D antiferromagnets,but also a promising candidate to design advanced nanodevices.

High-temperature ferromagnetic metallic phase in LaMnO_(3)/Sr_(3)Al_(2)O_(6)heterostructure

To achieve a flexible single-crystal multifunctional membrane,the freestanding process of a rigid epitaxial transition metal oxide thin film via a buffered water-dissolution sacrificial layer has attracted reasonable attentions.Owing to the difference in chemical potential,specific element affinity,and lattice constant between the target membrane and the sacrificial layer,the freestanding process may cause an indelible change of physics property once the target thin film is sensitive to the above factors.Here,the heterostructures composed of the generally adopted sacrificial layer Sr_(3)Al_(2)O_(6)(SAO)and LaMnO_(3)(LMO)have been systematically investigated.The electrical and magnetic properties of LMO show extreme sensitivity to the thickness of SAO(tSAO).Then we have also found that LMO/SAO heterostructures can exhibit the coexistence of two ferromagnetic phases,the significantly enhanced Curie temperature~342 K,and the large magnetoresistance-23.3%at 300 K,which is similar to the optimal-doped manganite such as La_(2/3)Sr_(1/3)MnO_(3).X-ray diffraction results show that continuously tunable strain from out-of-plane tension to relaxation and then to compression can be generated by adjusting tSAO.This strain can stabilize the migrated oxygen from LMO to SAO,which is induced by the large oxygen affinity difference between Bsite Mn and Al.It is believed that these unexpected electrical/magnetic phenomena are originated from the combined effects of interfacial element diffusion and strain.Our study provides a strategy for designing new magnetic phases,and a reference for the fundamental understanding of strongly correlated transition metal oxide systems in the freestanding process.

Amorphous nonstoichiometric oxides with tunable room-temperature ferromagnetism and electrical transport

Material functionalities strongly depend on the stoichiometry,crystal structure,and homogeneity.Here we demonstrate an approach of amorphous nonstoichiometric inhomogeneous oxides to realize tunable ferromagnetism and electrical transport at room temperature.In order to verify the origin of the ferromagnetism,we employed a series of structural,chemical,and electronic state characterizations.Combined with electron microscopy and transport measurements,synchrotron-based grazing incident wide angle X-ray scattering,soft X-ray absorption and circular dichroism clearly reveal that the roomtemperature ferromagnetism originates from the In0.23Co0.77O1-v,amorphous phase with a large tunable range of oxygen vacancies.The room-temperature ferromagnetism is tunable from a high saturation magnetization of 500 emu cm-3 to below 25 emu cm-3,with the evolving electrical resistivity from5×103μΩ cm to above 2.5×105 μΩ cm.Inhomogeneous nano-crystallization emerges with decreasing oxygen vacancies,driving the system towards non-ferromagnetism and insulating regime.Our work unfolds the novel functionalities of amorphous nonstoichiometric inhomogeneous oxides,which opens up new opportunities for developing spintronic materials with superior magnetic and transport properties.