Chiral antiferromagnetic (AFM) Mn3Sn has garnered extensive attention due to its remarkable room-temperature anomalous Hall effect (AHE). However, the structural and magnetic modulation mechanisms governing the long-range chiral AFM spin texture in Mn3Sn thin films remains insufficiently understood. In this work, highly ordered chiral AFM Mn3Sn(101̅0) thin films were epitaxially grown on MgO(110) substrates by molecular beam epitaxy. A prominent AHE response was observed at 300K, with anomalous Hall resistivity and conductivity reaching 4 μΩ cm and 44 Ω-1 cm-1, respectively. The anomalous Hall angle θAH was determined to be 1.33%, which is superior to the values reported for high-quality bulk Mn3Sn single crystals. Owing to the narrow growth window of Mn3Sn thin films, simultaneous optimization of crystalline quality and chiral spin ordering cannot be achieved merely by tuning the growth conditions. Our results reveal that moderate Mn-rich growth effectively improves the crystallinity of as-grown films. In comparison, post-growth thermal annealing facilitates the migration and lattice incorporation of residual Mn atoms during Mn3Sn lattice relaxation, which effectively optimizes the long-range chiral AFM ordering and further enhances the AHE performance. This work proposes a feasible strategy to modulate the chiral AFM spin structure of Mn3Sn thin films through synergistic regulation of Mn/Sn stoichiometry and thermal treatment, which provides valuable insights for the development of AFM spintronic devices.

The large anomalous Hall effect (AHE) in antiferromagnetic(AFM) Weyl semimetal Mn3Sn attracts intensive attentions in spintronics. Here, we report the structural property of high quality Mn3Sn thin film on insulator substrate MgO(1 1 0) by molecular beam epitaxy (MBE), and AHE in control of residual mismatch strain between Mn3Sn film and substrate. We are able to grow strain-free Mn3Sn(10 1 0) films or alternatively strained Mn3Sn(11 2 0) films via a three-step process. The strain-free Mn3Sn film has large anomalous Hall conductivity up to 30 & omega;-1cm- 1 at room temperature, which is comparable to bulk Mn3Sn. In contrast, AHE is switched off in strained Mn3Sn film due to piezomagnetic effect under a uniaxial compress strain of-2.0%. These findings provide a deeper understanding on AFM spintronic applications.

A novel sensor based on Schottky junction inducing avalanche breakdown effect in TiO 2 -Sn 3 O 4 nanoheterojunctions is assembled. High sensitivity for NO 2 gas sensing is demonstrated at room temperature. TiO 2 -Sn 3 O 4 nanocompositewas synthesized as the gas sensing layer and Schottky contact was formed by Au electrodes. The Schottky contact functions as a “gate” which can trigger the avalanche breakdown effect in the TiO 2 -Sn 3 O 4 heterojunctions. By tuning the Schottky barrier height through the responsive variation of the surface chemisorbed gas and the bias on the device, NO 2 at a concentration from 5 to 50 ppm can be detected with an average response time of 8s at room temperature. This nanostructured device is a promising candidate for application in high-sensitivity and high-speed NO 2 gas sensor. The methodology and working principle illustrated in this paper present a new sensing mechanism that can be readily and extensively applied to other gas sensing systems.

Low-dimensional materials have been drawing increasing interest due to the unique structures and fascinating properties which are quite promising for wide-range application ranging from new energy resources to information technology. The exotic electronic states of the low-dimensional materials which arise from the quantum-confinement effects of electrons render a potential strategy to overcome the size-limitation of traditional semiconducting materials and continue the Moores’ law which is difficult for the conventional bulk materials. The electronic structure modulation of low-dimensional materials to meet the relevant requirements serves as the key to reach this goal. Notably, in low-dimensional materials, the defect effects are more remarkable than those in bulk materials due to the high specific surface area and quantum confinement effects. Moreover, the compatibility of low-dimensional materials to nanoscaled devices is crucial for the next-generation device applications. Here, we focus on the role of defects in electronic structure modulation of one- (1D) and two-dimensional (2D) materials to summarize works of our group relevant to this topic in recent years. The point defects, such as vacancies and adatoms (or functional groups) are revealed to have significant contribution to the electron spin-polarization and excited states. The ferromagnetism of the metal-free materials is demonstrated in wide range of materials, such as graphite, hexagonal boron nitride and silicon carbide both theoretically and experimentally. The spin-polarization of p electrons in these materials enriches the family of ferromagnetic materials and offers a promising strategy for spintronics device applications. The hollow structure of carbon nanotubes provides an ideal platform for the study of atomic reaction, diffusion and condensation processes confined in nanospace. The electronic band structures of carbon nanotubes can be effectively regulated by encapsulating metal or hydrogen nanowires. Ultrahigh density of hydrogen nanowires can be confined inside carbon nanotubes, thanks to the excellent mechanical properties, which lead to metallization or superconductivity of the 1D hydrogen systems at relative low pressure and high temperature, due to the “physical compression” effect of carbon nanotubes. The superconducting hydrogen can be well explained in terms of the Eliashberg superconductivity theory for electron-phonon strong-coupling system. The metallization and superconducting phase of hydrogen nanowires encapsulated in carbon nanotubes open a promising platform for study of low-dimensional superconductivity at high pressure. Additionally, metal-organic frameworks (MOFs) which are composed of transition metal (TM) atoms and organic ligands emerged as a new family of 2D materials. Compared with traditional 2D materials, MOFs have the advantages of structural diversity, porous configurations, tunable electronic band structures. Some lattice models, such as Kagome, Lieb and Ruby lattice models can be achieved in 2D MOFs. The synergistic effect of TM atoms and organic ligands leads to exotic properties, such as Kane fermions, topological electronic states (quantum spin Hall effects and quantum anomalous Hall effect), superconductivity, high catalytic activity, etc. The well-distributed TM atoms in the porous structures of 2D MOFs facilitate the catalysis in hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which hold great promise in water splitting and fuel cells. In view of the experimental progresses on the synthesis of diverse 2D MOFs, the fascinating properties of 2D MOFs bring about new concepts for electronic devices and catalysis design.

We report an unconventional carrier-dependent anomalous Hall effect (AHE) with a quadratic scaling relation in epitaxial films of a ferromagnetic semiconductor (ZnCo)O with a high Co concentration. We show the co-existence of AHE together with the nonlinear ordinary Hall effect (NLHE) and the separation of NLHE by using a two-conducting channels model in the expression of Hall resistivity. We found that the NLHE depends strongly on both temperature and carrier density n and dominates at low temperature when n <1.0×1020cm−3, indicating the very necessary of separation them from each other for a proper scaling of the AHE. The anomalous Hall resistivity is nearly independent on carrier density and longitudinal resistivity regardless the underlying transport mechanisms and thermal properties. Very interestingly, a quadratic scaling relation between anomalous Hall conductivity and longitudinal conductivity σxyAHE∝σxx2 is obtained. The further analysis shows that σxyAHE∝n2 with a frozen electron mobility. In addition, sign reversal of the AHE has been observed by reducing magnetization via growth controlling engineering. Our results reveal a carrier-dependent AHE in low conductivity regime and provide an experimental evidence for the itinerant ferromagnetism in ferromagnetic semiconductor (ZnCo)O.

Novel spintronic devices with low power consumption, nonvolatility, and high storage density are highly desired to meet the rapid development of modern information storage and communication technology, which poses a great challenge to both material and device researches. To overcome this challenge, our group has focused our research on the following two aspects. On one hand, we have explored novel magnetoresistance effects in a variety of materials and devices, aiming to get a deep understanding about the spin dependent transport and obtain an effective control of spin-dependent transport. On the other hand, we have tried to control the magnetoresistance based on multi-physical field effects, aiming to obtain spintronic prototype devices that can be used for multi-state data storage. Regarding the novel magnetoresistance explorations, this article will introduce: (1) The negative magnetoresistance in amorphous condensed magnetic semiconductors. The spin dependent variable range hopping model is proposed, which can quantitatively explain the temperature and magnetic field dependent transport behavior in the condensed magnetic semiconductors. In addition, this model provides an alternative way to detect the spin polarization ratio of the magnetic semiconductors. (2) The positive magnetoresistance in single-crystal CoZnO magnetic semiconductors. By quantitative analysis of the transport properties of CoZnO films, it is observed that the positive magnetoresistance in the "hard gap" regime is the result of the carrier wavefunction shrinkage under applied magnetic field. (3) The rectification magnetoresistance in non-magnetic Schottky heterojunctions and the tunneling rectification magnetoresistance in magnetic tunnel junctions. A brand new rectification magnetoresistance is observed in nonmagnetic Al/Ge Schottky heterojunctions: The application of a pure small sinusoidal alternating current to the nonmagnetic Schottky heterojunctions can generate a significant direct-current voltage, and this rectification voltage strongly varies with the external magnetic field. Moreover, by using CoO-ZnO composite tunneling barrier, the charge-related rectification and spin-dependent tunneling magnetoresistance are integrated into the Co/CoO-ZnO/Co magnetic tunneling junctions to realize the tunneling rectification magnetoresistance. The observation of rectification magnetoresistance and tunneling rectification magnetoresistance not only adds new members to the magnetoresistance family, but also provides a promising way to control the devices' properties by using alternating current. In terms of multistate data storage application, this review will introduce: (1) The electrical and magnetic field controllable 4 resistance states in oxide heterojunctions. In Co/CoO-ZnO/Co magnetic tunneling junctions, by integrating the electrical field induced resistance switching and the magnetic field induced tunneling magnetoresistance effects, four nonvolatile resistance states are demonstrated. (2) The remanent magnetization controllable 10 resistance states in magnetic heterojunctions. Here, a general remanent magnetism engineering method is proposed for realizing multiple reliable magnetic and resistance states, not depending on a specific material or device structure. Especially, as a proof-of-concept demonstration, ten states of nonvolatile memory based on the manipulation of ferromagnetic remanent magnetization have been revealed in both Co/Pt magnetic multilayers with strong perpendicular magnetic anisotropy and MgO-based magnetic tunneling junctions at room temperature. (3) The spin-orbit torque controllable 10 resistance states in single-layer magnetic alloy. A repeatable bulk spin-orbit torque switching of the perpendicularly magnetized CoPt alloy single-layer films is realized by introducing a composition gradient in the thickness direction to break the inversion symmetry. Moreover, a ten states nonvolatile memory is illustrated solely by changing the electrical current to control the multi-domain states of the CoPt alloy.

Via exploring the spin dynamics and transport properties at interfaces of magnetic material/non-magnetic metal bilayers, spintronics advanced many techniques on generation, detection. and manipulation of spin currents. which laid down a foundation for designing spintronic devices. New ideas and methods for manipulating spin are required in the spintronics community. Merging with cavity quantum electrodynamics, magnetic resonance in ferromagnets inside of a microwave cavity, realizes a strong magnon-microwave coupling at room temperature, opening an avenue to manipulate spin and spin current for the spintronics community. Spin-microwave coupling strength was significantly improved by replacing a few spins in a paramagnetic spin system with magnetization in ferromagnetic materials. Thus. a strongly coupled magnon-microwave system offers a hybrid quantum platform with many measures to tune the coupled system, such as an exchange magnetic field, an anisotropy field, controlled coupling strength, controlled damping parameters, and so on. Many devices were proposed and demonstrated with potential applications. In this review, we briefly introduce the concept and mechanism of magnon-microwave coupling, a classical electrodynamical coupling model for the coupling, spin currents produced by the coupled magnon, and manipulation of the spin current via the strong coupling. In ferromagnets, magnon can couple to a microwave mode as a magnon-polariton propagating in the materials. The strongly coupled magnon-microwave system is a magnon-polariton in a cavity where the microwave was confined as a resonance mode with a high quality factor. Using the Landau-Lifshitz-Gilbert equation and Maxwell equations, we introduce the classical electrodynamical coupling model and reveal that the magnon is driven by a torque produced by the microwave magnetic field on the magnetization and the microwave is feedback via Faraday's law. Therefore, the coupling strength of the magnon-microwave system can be controlled by changing the torque. Magnon-microwave coupling is experimentally studied using many techniques, such as microwave transmission, Brillouin light scattering. Faraday rotation measurement, and spin pumping electrical detection. Spin pumping is well explored in the spintronics community as a spin current produced by magnon and detected as a voltage via inverse spin Hall effect in a novel metal. Combining with microwave transmission of the coupled microwave subsystem, spin pumping electrical detection by directly detecting the spin current produced by the magnon subsystem in the coupled system, illustrates a more complete profile of the coupled magnon-microwave system. In addition, the strongly coupled magnon-microwave system offers a new technique to manipulate spin currents. We experimentally demonstrate that spin currents produced by the strongly coupled system are correlated with each other mediated by the microwave cavity, and can be manipulated remotely. Two almost identical magnet samples am used to couple to a cavity and the coupling strengths between each magnet and the cavity are tunable individually. By using electrical detection to locally detect each magnet sample respectively, we find that the spin currents produced by two magnet samples are coherently correlated. By tuning the coupling strength of one magnet sample to the cavity. the spin current produced by the second magnet sample is manipulated distantly over a few centimeters, which is far longer than the distance of spin-orbit interaction or exchange interaction. This distant control is only limited by the coherence length of the microwave and the dimension of the cavity. This flexibility opens the door to improve spin current generation and manipulation for cavity spintronic devices.

In this paper, we demonstrate the ferroelectric gate control of Rashba–Dresselhaus spin–orbit coupling (R–D SOC) in a hybrid heterostructure consisting of a ferromagnetic semiconductor channel (Zn, Co)O(0001) and a ferroelectric substrate PMN-PT(111). The R–D SOC causes a transverse spin current via the charge-spin conversion, which results in unbalanced transverse spin and charge accumulations due to the spin-polarized band in the ferromagnetic (Zn, Co)O channel. By the reversal of gated ferroelectric polarization, we observed 55% modulation of the R–D SOC correlated Hall resistivity to the magnetization correlated anomalous Hall resistivity and 70% modulation of the low-field magnetoresistance at 50 K. Our experimental results pave a way toward semiconductor-based spintronic-integrated circuits with an ultralow power consumption in ferromagnetic semiconductors.

Manipulation of oxygen vacancies (V-o) in transition metal oxides (TMOs) can largely alter their physical and chemical properties, such as electrical conductivity, magnetic state, optical band-gap, and electrocatalytic reactivity. Many experimental and theoretical works have been conducted to study the formation/annihilation of V-o and its corresponding effect on the properties in TMOs. In this paper, a solid-state approach to modulate the oxygen stoichiometry in high quality SrCoOx epitaxial thin films was demonstrated. Dependence of the magnetic and electrical conducing properties on V-o was investigated. Room temperature reversible phase switching between brownmillerite antiferromagnetic insulating SrCoO2.5 and perovskite ferromagnetic metallic SrCoO3-delta was achieved by electric-field induced oxygen non-stoichiometry. This room temperature reversible phase switching indicates that SrCoOx thin films are a promising candidate for practical applications in resistive random access memory and spintronic devices.

First-principles calculations are performed to explore the possibility of generating the two-dimensional electron gas (2DEG) at the interface between LaGaO3/KTaO3 and NdGaO3/KTaO3 (001) heterostructures. Two different models - i.e., the superlattice model and the thin film model - are used to conduct a comprehensive investigation of the origin of charge carriers. For the symmetric superlattice model, the LaGaO3 (or NdGaO3) film is nonpolar. The 2DEG with carrier density on the order of 10(14)cm(-2) originates from the Ta d(xy) electrons contributed by both LaGaO3 (or NdGaO3) and KTaO3. For the thin film model, large polar distortions occur in the LaGaO3 and NdGaO3 layer, which entirely screens the built-in electric field and prevents electrons from transferring to the interface. Electrons of KTaO3 are accumulated at the interface, contributing to the formation of the 2DEG. All the heterostructures exhibit conducting properties regardless of the film thickness. Compared with the Ti d(xy) electrons in SrTiO3-based heterostructures, the Ta d(xy) electrons have small effective mass and they are expected to move with higher mobility along the interface. These findings reveal the promising applications of 2DEG in novel nanoelectronic devices.

The magnetization-direction-dependent inverse spin Hall effect (ISHE) has been observed in NiFe film during spin Seebeck measurement in IrMn/NiFe/Cu/yttrium iron garnet (YIG) multilayer structure, where the YIG and NiFe layers act as the spin injector and spin current detector, respectively. By using the NiFe/IrMn exchange bias structure, the magnetization direction of YIG (M YIG) can be rotated with respect to that of NiFe (M NiFe) with a small magnetic field, thus allowing us to observe the magnetization-direction-dependent inverse spin Hall effect voltage in NiFe layer. Compared with the situation that polarization direction of spin current (σ s) is perpendicular to M NiFe, the spin Seebeck voltage is about 30% larger than that when σ s and M NiFe are parallel to each other. This phenomenon may originate from either or both of stronger interface or bulk scattering to spin current when σ s and M NiFe are perpendicular to each other. Our work provides a way to control the voltage induced by ISHE in ferromagnets.

fDensity functional theory within the generalized gradient approximation is employed to investigate the two-dimensional electron gas (2DEG) at the interface of NdGaO3/SrTiO3 (001) heterostructure. For the superlattice model, the 2DEG originates from the Ti dxy electrons, which are transferred from the NdGaO3 side. However, the interface of the thin film model exhibits insulated properties. In order to investigate the different properties of the two models, it is noted that large polar distortion in the NdGaO3 side occurs in the thin film model comparing to the superlattice model, and the built-in electric field is screened by the large distortion, and result in preventing the electron transfer from the NdGaO3 side to Ti dxy orbitals. For the thin film model, the surface layer of NdGaO3 is the energy favor position of oxygen vacancy, which results in the rotation of the oxygen octahedrons. The 2DEG is induced by the balance between the distortion by the surface and the oxygen octahedrons rotation by the oxygen vacancy. (C) 2018 Published by Elsevier B.V.

On the face of the impending energy crisis, developing low-energy consuming photoelectronic devices is extremely important. A wide spectral photosensitivity feature of a self-powered device provides an additional powerful tool. In this letter, a Ag2S/ZnO core-shell nanoheterojunction was prepared and a high performance self-powered solid-state photodetector was developed based on this nanostructure. High quality, vertically aligned ZnO nanoneedle arrays loaded with Ag2S quantum dotes were grown on FTO glass substrate by wet chemical methods. The microstructure and surface morphology of the prepared samples were characterized by transmission electron microscopy and scanning electron microscopy. A solid-state self-powered photodetector was assembled using this ZnO/Ag2S core-shell nanostructure as the photoanode. The photodetector shows a high photosensitivity in the wide spectral range from 400 to 1100 nm, and its response time is as short as 5 ms. Considering its excellent performance and easy fabrication process, this Ag2S/ZnO core-shell nanoheterojunction is an ideal candidate for wide spectral photodetecting application. (C) 2017 Elsevier B.V. All rights reserved.

Photoelectrochemical cell-typed self-powered UV detectors have attracted intensive research interest due to their low cost, simple fabrication process, and fast response. In this paper, SnO2-TiO2 nanomace arrays composed of SnO2 nanotube trunk and TiO2 nanobranches were prepared using soft chemical methods, and an environment-friendly self-powered UV photodetector using this nanostructure as the photoanode was assembled. Due to the synergistic effect of greatly accelerated electron-hole separation, enhanced surface area, and reduced charge recombination provided by SnO2-TiO2 nanomace array, the nanostructured detector displays an excellent performance over that based on bare SnO2 arrays. The impact of the growing time of TiO2 branches on the performance of UV photodetector was systematically studied. The device based on optimized SnO2-TiO2 nanomace arrays exhibits a high responsivity of 0.145 A/W at 365 nm, a fast rising time of 0.037 s, and a decay time of 0.015 s, as well as excellent spectral selectivity. This self-powered photodetector is a promising candidate for high-sensitivity, high-speed UV-detecting application.

We report electric field control of the interfacial Dzyaloshinskii-Moriya interaction (DMI) in MgO/Fe/Pt multilayers. The interfacial DMI is obtained and quantified by Brillouin light scattering measurements based on the frequency nonreciprocity of spin waves in a ferromagnet. The magnitude of the induced DMI is found to linearly increase as a function of electric field intensity. The efficiency of electric field control of the interfacial DMI characterized as a ratio of the DMI energy change to the electric field, which is found to be equal to 67 fJ/(Vm) with a positive electric field. We further demonstrate that the origin of the enhanced DMI results from the MgO/Fe interface. The Rashba spin-orbit coupling and electric field induced anisotropy at the MgO/Fe interface might be responsible for the enhanced interfacial DMI. Our findings open up a way for exploring the spintronic devices with a tunable DMI.

Direct evidence of purely interfacial effects on resistance switching is demonstrated in Au/BiFeO3/Nd:SrTiO3(001) (Au/BFO/NSTO) Schottky junctions by reducing the thickness of ferroelectric interlayer BFO.

Photodetectors with excellent detecting properties over a broad spectral range have advantages for the application in many optoelectronic devices. Introducing imperfections to the atomic lattices in semiconductors is a significant way for tuning the bandgap and achieving broadband response, but the imperfection may renovate their intrinsic properties far from the desire. Here, by controlling the deviation from the perfection of the atomic lattice, ultrabroadband multilayer MoS2 photodetectors are originally designed and realized with the detection range over 2000 nm from 445 nm (blue) to 2717 nm (mid-infrared). Associated with the narrow but nonzero bandgap and large photoresponsivity, the optimized deviation from the perfection of MoS2 samples is theoretically found and experimentally achieved aiming at the ultrabroadband photoresponse. By the photodetection characterization, the responsivity and detectivity of the present photodetectors are investigated in the wavelength range from 445 to 2717 nm with the maximum values of 50.7 mA W-1 and 1.55 × 109 Jones, respectively, which represent the most broadband MoS2 photodetectors. Based on the easy manipulation, low cost, large scale, and broadband photoresponse, this present detector has significant potential for the applications in optoelectronics and electronics in the future.

Density functional theory within the local density approximation is used to investigate the effect of the oxygen vacancy on the LaGaO3/SrTiO3 (001) heterojunction. It is found that the energy favorable configuration is the oxygen vacancy located at the 3rd layer of the STO substrate, and the antiferrodistortive distortion is induced by the oxygen vacancy introduced on the SrTiO3 side. Compared with the heterojunction without introducing oxygen vacancy, the heterojunction with introducing the oxygen vacancy does not change the origin of the two-dimensional electron gas (2DEG), that is, the 2DEG still originates from the d(xy) electrons, which are split from the t(2g) states of Ti atom at interface; however the oxygen vacancy is not beneficial to the confinement of the 2DEG. The extra electrons caused by the oxygen vacancy dominantly occupy the 3d(x2-y2) orbitals of the Ti atom nearest to the oxygen vacancy, thus the density of carrier is enhanced by one order of magnitude due to the introduction of oxygen vacancy compared with the density of the ideal structure heterojunction.