Oxygen Ion Migration Research Articles

Room-temperature-processed synaptic a-IGZO TFT with high-k HfLaO gate dielectric as neuromodulator

In this work, room-temperature-processed amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) have been fabricated with high-k HfLaO as gate dielectric for synaptic devices. By raising the indium content in the a-IGZO film via co-sputtering and treating the HfLaO gate dielectric in an Ar plasma, the TFT with In1.0Ga3.0Zn0.4O2.1 presents excellent electrical characteristics: a high intrinsic carrier mobility of 45.8 cm2 V−1·s−1, a small threshold voltage of 1.93 V, a small hysteresis of −0.015 V, and a small subthreshold swing (SS) of 0.21 V dec−1. Although the oxygen vacancies in the In1.0Ga3.0Zn0.4O2.1 TFT are increased to produce a high carrier mobility, memristive behaviors are hardly observed under zero gate bias due to their occupied states. Various conductance modulations and synaptic plasticities are achieved under a 2-V drain spiking voltage and a small gate bias of 1 V due to migration of oxygen ions and emptying/detrapping of oxygen vacancies in the In1.0Ga3.0Zn0.4O2.1 film, resulting in a concurrent emulation of neurotransmitter and neuromodulator through exploiting the native three-terminal structure of the TFT.

Oxidation Kinetics of Nanocrystalline Hexagonal RMn1-xTixO3 (R = Ho, Dy).

Hexagonal manganites, RMnO3 (R = Sc, Y, Ho-Lu), are potential oxygen storage materials for air separation due to their reversible oxygen storage and release properties. Their outstanding ability to absorb and release oxygen at relatively low temperatures of 250-400 °C holds promise of saving energy compared to current industrial methods. Unfortunately, the low temperature of operation also implies slow kinetics of oxygen exchange in these materials, which would make them inefficient in applications such as chemical looping air separation. Here, we show that the oxidation kinetics of RMnO3 can be improved through Ti4+-doping as well as by increasing the rare earth cation size. The rate of oxygen absorption of nanocrystalline RMn1-xTixO3 (R = Ho, Dy; x = 0, 0.15) was investigated by thermogravimetric analysis, X-ray absorption near-edge structure, and high-temperature X-ray diffraction (HT-XRD) with in situ switching of atmosphere from N2 to O2. The kinetics of oxidation increases for larger R and even more with Ti4+ donor doping, as both induce expansion of the ab-plane, which reduces the electrostatic repulsion between oxygen in the lattice upon oxygen ion migration. Surface exchange rates and activation energies of oxidation were determined from changes in lattice parameters observed through HT-XRD upon in situ switching of atmosphere.

A Sr2CoNbO6-δ@Sm0.2Ce0.8O2- δ nanofiber composite as cathode accelerates oxygen reduction reaction for IT-SOFC

Boosting the lower oxygen reduction reaction (ORR) activity of perovskite cathode material is essential for the development and widespread use of IT-SOFC. Oxygen ion migration at the cathode-electrolyte interface can enhance by introducing structural modifications consisting of high grain boundary density and heterointerfaces [1]. Herein, we fabricated Sr2CoNbO6- δ @Sm0.2Ce0.8O1.9 (SCNO@SDC) nanofiber composite using an electrospinning technique and examined the electrochemical impedance for the symmetric cell in air atmosphere. The distinct phases of SCNO and SDC were observed from XRD and FESEM-EDAX analysis. The ionic conductivity was analysed to monitor the electrochemical activity of synthesised material, and the results illustrated that the activation energy for the nanofiber was 0.51 eV lower than conventional composites’ 0.73 eV. The thermal expansion coefficient showed improvement as the value of 14.3 Х 10-6 K-1 for nanofiber composite than the 17.6 Х 10-6 K-1 of SCNO-SDC [2]. The symmetric SCNO|SDC|SCNO cell electrodes from nanofiber were fabricated, and electrochemical performance was compared with 20% SDC-SCNO composite in an air atmosphere with varying temperatures from 500oC to 700oC. Figure 1. compares polarisation resistance with increased temperature for nanofiber and conventional electrodes. The polarization resistance significantly decreased from 2.76 Ω cm2 to 0.69 Ω cm2 for the nanofiber composite than the conventional electrode 5.2 Ω cm2 to 2.1 Ω cm2 [3]. The sluggish ORR activity improved due to unique microstructure, high porosity, and specific surface area, which provides extensive triple phase boundaries and a continuous path for charge transfer [4]. Therefore, SCNO@SDC nanofiber composite offers an alternative approach for attaining efficient performance of IT-SOFC. References Choi, Y., Cho, H. J., Kim, J., Kang, J. Y., Seo, J., Kim, J. H., & Jung, W. (2022). Nanofiber Composites as Highly Active and Robust Anodes for Direct-Hydrocarbon Solid Oxide Fuel Cells. ACS nano, 16(9), 14517-14526.Li, Z., Peng, M., Zhao, Y., Li, J., & Sun, Y. (2021). Minimized thermal expansion mismatch of cobalt-based perovskite air electrodes for solid oxide cells. Nanoscale, 13(47), 20299-20308.Kumari, N., Tiwari, P. K., Haider, M. A., & Basu, S. (2017). Electrochemical performance of infiltrated Cu-GDC and Cu-PDC cathode for CO2 electrolysis in a solid oxide cell. ECS Transactions, 78(1), 3329.Zhao, B., Zhang, L., Zhen, D., Yoo, S., Ding, Y., Chen, D., & Liu, M. (2017). A tailored double perovskite nanofiber catalyst enables ultrafast oxygen evolution. Nature communications, 8(1), 1-9. Figure 1

Predicting Fast Oxygen Ion Conductors Via Descriptors for Migration Barrier Based on Electronic Structure and Lattice Dynamics

Solid-state oxygen ion conductors are of paramount importance to solid oxide fuel cells and electrolytic cells. However, with the oxygen ion conductors proposed to date, these technologies require too high (close to 800 oC) temperatures to operate, leading to technological challenges and high costs. Therefore, it is of primary importance to design faster oxygen ion conductors at intermediate and low temperatures (below 400 oC) that can enable sustainable energy technologies to mitigate climate change. Descriptors for oxygen ion conduction are highly desirable to identify promising materials, which can be done by leveraging fast-growing statistical and machine learning approaches for screening of material databases [1]. Recently, computational tools combined with experiments have allowed researchers to gain atomistic insights and relate ion transport to features of the lattice dynamics [2] and electronic structure [3] of a given material. In this work, building upon the previous literature, we leverage both the lattice dynamics and electronic structure to predict the migration barrier for oxygen migration in pure and mixed electronic ionic conductors and search for promising oxygen ion conductors.Using density functional theory simulations, we model oxygen migration in perovskite, rutile, fluorite, and Ruddlesden-Popperoxides. We analyze oxygen ion transport in pure and mixed electronic ionic conductors and oxygen vacancies with and without charge. We study changes in the electronic structure during oxygen migration within the solid host lattice in different oxides. By analyzing trends of migration barrier and electronic density of states, we relate the migration barrier to the electronic structure of the transition state. Our results show that the migration barrier depends on the capability that the host lattice has of screening charge associated with the mobile ion in the transition state, which if increased would lower the localization of charge around the mobile ion and in turn the oxygen migration barrier. In pure ionic conductors – where no charge is associated with the mobile ion - the migration barrier is largely dependent on the M-O strength. Based on the mechanistic understanding derived by these initial analyses, we further relate oxygen ion conductivity to the lattice dynamics. We show that in pure ionic conductors, increasing migration barrier follows trends of increasing oxygen vibrational frequency based on phonon-electron coupling, which also relates the prefactor of Arrhenius law with the migration barrier. However, when trying to predict trends of the migration barrier across different crystal structures or mixed ionic conductors, no single descriptor can capture the complex physiochemistry behind oxygen migration. Thus, we leverage statistical learning tools to identify multivariate descriptors and analyze specific features of lattice moieties that improve oxygen ion conduction. The results of this work provide mechanistic understanding of oxygen ion migration and strategies to accelerate the designs of fast oxygen ion conductors.

Sol-Gel-Processed Y2O3 Multilevel Resistive Random-Access Memory Cells for Neural Networks.

Yttrium oxide (Y2O3) resistive random-access memory (RRAM) devices were fabricated using the sol-gel process on indium tin oxide/glass substrates. These devices exhibited conventional bipolar RRAM characteristics without requiring a high-voltage forming process. The effect of current compliance on the Y2O3 RRAM devices was investigated, and the results revealed that the resistance values gradually decreased with increasing set current compliance values. By regulating these values, the formation of pure Ag conductive filament could be restricted. The dominant oxygen ion diffusion and migration within Y2O3 leads to the formation of oxygen vacancies and Ag metal-mixed conductive filaments between the two electrodes. The filament composition changes from pure Ag metal to Ag metal mixed with oxygen vacancies, which is crucial for realizing multilevel cell (MLC) switching. Consequently, intermediate resistance values were obtained, which were suitable for MLC switching. The fabricated Y2O3 RRAM devices could function as a MLC with a capacity of two bits in one cell, utilizing three low-resistance states and one common high-resistance state. The potential of the Y2O3 RRAM devices for neural networks was further explored through numerical simulations. Hardware neural networks based on the Y2O3 RRAM devices demonstrated effective digit image classification with a high accuracy rate of approximately 88%, comparable to the ideal software-based classification (~92%). This indicates that the proposed RRAM can be utilized as a memory component in practical neuromorphic systems.

Proton-Assisted Redox-Based Three-Terminal Memristor for Synaptic Device Applications

Emerging technologies, i.e., spintronics, 2D materials, and memristive devices, have been widely investigated as the building block of neuromorphic computing systems. Three-terminal memristor (3TM) is specifically designed to mitigate the challenges encountered by its two-terminal counterpart as it can concurrently execute signal transmission and memory operations. In this work, we present a complementary metal-oxide-semiconductor-compatible 3TM with highly linear weight update characteristics and a dynamic range of ∼15. The switching mechanism is governed by the migration of oxygen ions and protons in and out of the channel under an external gate electric field. The involvement of the protonic defects in the electrochemical reactions is proposed based on the bipolar pulse trains required to initiate the oxidation process and the device electrical characteristics under different humidity levels. For the synaptic operation, an excellent endurance performance with over 256k synaptic weight updates was demonstrated while maintaining a stable dynamic range. Additionally, the synaptic performance of the 3TM is simulated and implemented into a four-layer neural network (NN) model, achieving an accuracy of ∼92% in MNIST handwritten digit recognition. With such desirable conductance modulation characteristics, our proposed 3T-memristor is a promising synaptic device candidate to realize the hardware implementation of the artificial NN.

Electrical Control of Spin Hall Efficiency and Field-Free Magnetization Switching in W/Pt/Co/Pt Heterostructures with Competing Spin Currents.

Reversal of magnetization via current-induced spin-orbit torque (SOT) is one of the core issues in spintronics. However, an in-plane assistant field is usually required for the deterministic switching of a perpendicularly magnetized system. Additionally, the efficiency of SOT is low, which is detrimental to device applications. This study achieved a reversible and non-volatile control of the critical current for magnetization switching and spin Hall efficiency in the TaN/W/Pt/Co/Pt/TaN heterostructures by ionic liquid (IL) gating-induced hydrogen ion adsorption and desorption in the upper Pt layer. Furthermore, the thinning of the Pt and TaN capping layers activated the oxygen ion migration toward the Co layer under IL gating, resulting in an exchange bias field and allowing field-free magnetization switching and Boolean logic operation. The results of this study offer an intriguing opportunity to promote the development of SOT-based spintronic devices from the perspective of iontronics with low energy dissipation.

Electric modulation of anisotropic magnetoresistance in Pt/HfO2–x /NiO y /Ni heterojunctions

Electric field control of magnetism through nanoionics has attracted tremendous attention owing to its high efficiency and low power consumption. In solid-state dielectrics, an electric field drives the redistribution of ions to create one-dimensional magnetic conductive nanostructures, enabling the realization of intriguing magnetoresistance (MR) effects. Here, we explored the electric-controlled nickel and oxygen ion migration in Pt/HfO2−x /NiO y /Ni heterojunctions for MR modulation. By adjusting the voltage polarity and amplitude, the magnetic conductive filaments with mixed nickel and oxygen vacancy are constructed. This results in the reduction of device resistance by ∼103 folds, and leads to an intriguing partial asymmetric MR effect. We show that the difference of the device resistance under positive and negative saturation magnetic fields exhibits good linear dependence on the magnetic field angle, which can be used for magnetic field direction detection. Our study suggests the potential of electrically controlled ion migration in creating novel magnetic nanostructures for sensor applications.

Direct Observation of Oxygen Ion Dynamics in a WO3‐x based Second‐Order Memristor with Dendritic Integration Functions

AbstractDirect observation of oxygen dynamics in an oxide‐based second‐order memristor can provide the valid evidence to clarify the memristive mechanism, however, which is still limited for now. In this study, the migration and diffusion of oxygen ions in the region of Pt/WO3‐x Schottky interface are observed in the WO3‐x second‐order memristor by using the technique of in situ transmission electron microscopy (TEM) and the electron energy loss spectroscopy. Interestingly, the coexistence of memristive and memcapacitive switching can be implemented in this memristor. Combined with the analysis of depth‐profile X‐ray photoelectron spectroscopy (XPS), an interface‐barrier‐modulation second‐order memristive model is proposed based on the above results. Notably, temporally correlative oxygen dynamics in the memristor offers the platform to integrate signals from multiple inputs, enabling the realization of the dendritic functions of synchronous and asynchronous integration for the application of logic operations with fault‐tolerance capability and associative learning. These findings provide the experimental evidence to in‐depth understanding of oxygen dynamics and switching mechanism in second‐order memristor, which can support the optimization of memristive performance and the achievement of biorealistic synaptic functions.

Electrical Manipulation of Orbital Current Via Oxygen Migration in Ni81 fe19 /Cuox /Tan Heterostructure.

The orbital Hall effect and the interfacial Rashba effect provide new approaches to generate orbital current and spin-orbit torque (SOT) efficiently without the use of heavy metals. However, achieving efficient dynamic control of orbital current and SOT in light metal oxides has proven challenging. In this study, we demonstrate that a sizable magnetoresistance effect related to orbital current and SOT can be observed in Ni81 Fe19 /CuOx /TaN heterostructures with various CuOx oxidisation concentrations. The ionic liquid gating induces migration of oxygen ions, which modulates the oxygen concentration at the Ni81 Fe19 /CuOx interface, leading to reversible manipulation of the magnetoresistance effect and SOT. The existence of a thick TaN capping layer allows for sophisticated internal oxygen ion reconstruction in the CuOx layer, rather than conventional external ion exchange. These results provide a method for the reversible and dynamic manipulation of the orbital current and SOT generation efficiency, thereby advancing the development of spin-orbitronics devices through ionic engineering. This article is protected by copyright. All rights reserved.

Solution-processed small-molecular organic memristor with a very low resistive switching set voltage of 0.38 V

Organic memristors are considered to be the next-generation storage element due to their unique advantages of flexibility, transparency, and good solution processability. In this Letter, a Zn-porphyrin based small-molecular organic memristor is prepared by spin-coating with an ultralow resistive switching set voltage of 0.38 V. It is found that the zinc atom in the porphyrin molecule plays a very important role in improving the resistance switching characteristics of organic memristors. By tracking the change in oxygen valence in the vertical dimension, we demonstrate that Zn atom located in the core of porphyrin helps to enhance the oxygen ion migration across the active layer, clearly revealing the memory mechanism of low-cost solution-processed Zn-porphyrin based small-molecular organic memristors. This organic memristor shows excellent memristive performance resulting from rational material design and appropriate device structure engineering.

Promotion of MgO sorbents with eutectic carbonate doping for high-temperature and pressure CO2 capture

MgO-based sorbents are promising candidates for CO2 capture as they are widely available and feasible in thermodynamics, but the development of MgO-based sorbents operating at elevated temperature and pressure is still a challenging task due to sintering. Herein, we selected eutectic carbonates with high melting point as promoters for the application under elevated conditions. Among various eutectic carbonates, MgO with eutectic ternary LiNaK carbonate (ETC) doping exhibited the highest MgO conversion thanks to crystal defects based on the XRD analysis. The highest CO2 capture capacity of 0.73 gCO2/gsorbent was obtained with 20 wt% ETC at 400 °C and 2 MPa. With further elevation of operating parameters to 540 °C and 5 MPa, the sample still shows a stable MgO conversion of 0.69 after 30 cycles, where the material exhibits a porous structure that inhibits the sintering. The density function theory calculations reveal that the LiNaK doping lowers the formation energy of surface oxygen vacancy, providing possibility for the subsequent oxygen ion migration. The deep K incorporation is most effective to promote the oxygen ion diffusion with decreased oxygen ion migration energy barrier from 3.68 to 2.04 eV. This study can guide the design of high-performance CO2 sorbents at wider application conditions.

Electric-Controlled Resistive Switching and Different Synaptic Behaviors in p⁺-Si/n-ZnO Heterojunction Memristor

In this study, the resistive switching (RS) and different synaptic behaviors have been observed by controlling the different applied bias voltages in the p <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{+}$</tex-math> </inline-formula> -Si/n-ZnO heterojunction memristor. After a big forming voltage, the formation and rupture of the oxygen vacancy filaments model has been proposed, and different migration amount of oxygen ions realizes the multiple RS behaviors. Prior to the electroforming, different synaptic behaviors have been observed dependent on the applied bias voltage based on the oxygen ion migration processes. Under small bias ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt;$</tex-math> </inline-formula> 2.5 V), the oxygen ion of ZnO film first migrates and inters into p/n-junction barrier region, leading to the increasing barrier height/width. With increasing voltage, the electric field will further induce oxygen ion migration and entrance to Si film, leading to the decreasing barrier height/width. Several synaptic functions are demonstrated, such as nonlinear transmission characteristics, long-term memory (LTM)/short-term memory (STM) and “learning-experience” behavior. Multifunction memristive behaviors and these mechanisms research are important to design and realize the multifunction devices for decreasing the manufacturing complexity.

Role of Oxygen in Vacancy-Induced Phase Formation and Crystallization of Al2TiO5-Based Chemical Vapor-Deposited Coatings

Oxygen is a commonly overlooked element influencing the properties of many metal oxides. By combining several analytical in situ techniques and theoretical calculations, we demonstrate that oxygen plays a vital part in the phase formation and crystallization of Al2TiO5-based chemical vapor-deposited coatings. Rutherford backscattering spectrometry (RBS) corroborates a polymorphic transformation during crystallization. Subsequent hard X-ray photoelectron spectroscopy (HAXPES) shows that crystallization occurs through a displacive (diffusionless) mechanism. Coupled with theoretical calculations, the crystallization and co-formation of Al2TiO5, Al6Ti2O13, and Al16Ti5O34 are suggested to be driven by the migration of oxygen ions and their corresponding vacancies.

Enhancement of spin–orbit torque in Pt/Co/HfOx heterostructures with voltage-controlled oxygen ion migration

Spin–orbit torque (SOT) induced magnetization switching and SOT modulation by interfacial coupling exhibit good potential in spintronic devices. In this work, we report the enhancement of damping-like field and SOT efficiency of up to 60% and 23%, respectively, in perpendicularly magnetized Pt/Co/HfOx heterostructures over a Pt/Co system at an optimal thickness of 2 nm HfOx. The SOT improvement is primarily attributed to the interfacial oxidization of the Co layer, and the strength is tunable via voltage-induced oxygen ion migration at the Co/HfOx interface. Our measurement reveals that by controlling gate voltages, the Co oxidation can be increased, which leads to the SOT efficiency enhancement. Our work promotes the SOT enhancement and modulation by oxidation effects for energy-efficient spintronic devices.

Tin Oxide Nanorod Array-Based Photonic Memristors with Multilevel Resistance States Driven by Optoelectronic Stimuli

One-dimensional (1D) metal oxide-based photonic memristors, combining information storage and optical response, have shown great potential for the design and development of high-density and high-efficient computing systems beyond the era of von-Neumann architecture and Moore's law. Here, the functional memristive devices based on SnOx slanted nanorod arrays are demonstrated; wherein both the optical and electrical stimuli have been used to modulate the switching characteristics to achieve multilevel cell operations. The switching characteristics of Al/SnOx/FTO devices include low operating voltages (0.7 V/-0.6 V), moderate ON/OFF ratio (>10), and longer endurance (>102 cycles) and retention (>103 s) with a self-compliance effect in the dark. Under illumination, ranging from ultraviolet (254 and 365 nm) to visible light (405 and 533 nm), an unusual negative photo response with an enlarged ON/OFF ratio of >107 and a faster response time of <8 ms is observed. Additionally, multiple low and high resistance states have been achieved by modulating the programming current and the optical stimulus, respectively. The optoelectronic resistive memory behavior is attributed to the electric field-induced formation and light-stimulated dissolution of oxygen vacancies. Comprehensively, the results suggest that the optical illumination reduces the oxygen ion migration barrier, leading to the dissolution of conductive filaments and thereby locally increasing the OFF state resistance. The fabricated photonic memristors demonstrate the potential applications of metal oxide-based 1D nanostructures for artificial visual memory and optoelectronic applications.

Resistive switching properties of SnO2 nanowires fabricated by chemical vapor deposition

Resistive switching (RS) devices have great application prospects in the emerging memory field and neuromorphic field, but their stability and unclear RS mechanism limit their relevant applications. In this work, we construct a hydrogenated Au/SnO2 nanowire (NW)/Au device with two back-to-back Schottky diodes and investigate the RS characteristics in air and vacuum. We find that the I on/I off ratio increases from 20 to 104 when the read voltage decreases from 3.1 V to −1 V under the condition of electric field. Moreover, the rectification ratio can reach as high as 104 owing to oxygen ion migration modulated by the electric field. The nanodevice also shows non-volatile resistive memory characteristic. The RS mechanism is clarified based on the changes of the Schottky barrier width and height at the interface of Au/SnO2 NW/Au device. Our results provide a strategy for designing high-performance memristive devices based on SnO2 NWs.

In Operando Optical Tracking of Oxygen Vacancy Migration and Phase Change in few Nanometers Ferroelectric HZO Memories

AbstractFerroelectric materials offer a low‐energy, high‐speed alternative to conventional logic and memory circuitry. Hafnia‐based films have achieved single‐digit nm ferroelectricity, enabling further device miniaturization. However, they can exhibit nonideal behavior, specifically wake‐up and fatigue effects, leading to unpredictable performance variation over consecutive electronic switching cycles, preventing large‐scale commercialization. The origins are still under debate. Using plasmon‐enhanced spectroscopy, a non‐destructive technique sensitive to &lt;1% oxygen vacancy variation, phase changes, and single switching cycle resolution, the first real‐time in operando nanoscale direct tracking of oxygen vacancy migration in 5 nm hafnium zirconium oxide during a pre‐wake‐up stage is provided. It is shown that the pre‐wake‐up leads to a structural phase change from monoclinic to orthorhombic phase, which further determines the device wake‐up. Further migration of oxygen ions in the phase changed material is then observed, producing device fatigue. These results provide a comprehensive explanation for the wake‐up and fatigue with Raman, photoluminescence and darkfield spectroscopy, combined with density functional theory and finite‐difference time‐domain simulations.

Conductivities in Yttrium-Doped Barium Zirconate: A First-Principles Study

Yttrium-doped barium zirconate (BZY) has emerged as an attractive candidate for application as a proton (H+)-conducting solid electrolyte due to its high ionic conductivity and excellent chemical stability. In this study, the conductivities of BaZr(1−x)YxO3−δ (BZY, x = 0, 0.037, 0.074, 0.148, and 0.22) with different carriers were studied based on density functional theory (DFT) and experiments. The results revealed that yttrium doping can effectively reduce the energy barrier for the migration of protons and oxygen ions (O2−). When comparing the energy barriers for protons and oxygen ions, the energy barriers for proton migration were found to be lower than those for oxygen ion migration, which indicates that a proton conductor can offer the advantages of lower activation energy and, possibly, higher conductivity. An analysis of the electronic structure of the BZYs found that the top of the valence band exceeded the Fermi energy level following yttrium doping. As a result, the electron conductivity increased as the yttrium content increased. Furthermore, this study also tested the total conductivity of BaZr(1−x)YxO3−δ (BZY, x = 0.1, 0.2, 0.3, and 0.4) and found the trend of the total conductivity to be consistent with the results of the DFT calculations.

Novel coexistence of resistive switching and ferromagnetism modulation in Ta/La2/3Sr1/3MnO3/Nb:SrTiO3/Ag device

The Ta/La2/3Sr1/3MnO3/Nb:SrTiO3/Ag device has novel coexistence of resistive switching and ferromagnetism modulation. The inactive Ta electrode can effectively balance the Schottky barrier height on both sides of La2/3Sr1/3MnO3, making the current–voltage (I–V) curves of the device exhibit symmetry. The conduction mechanism of the device is conductive filaments of oxygen vacancies at low resistance state (LRS), and Schottky barrier at high resistance state (HRS). The migration of oxygen ions affects not only the resistance but also the ferromagnetism of the device. The suppression of double exchange effect by oxygen vacancies results in higher saturation magnetization (Ms) at HRS than at LRS. Our first-principles calculations are consistent with the experimental results. The stable coexistence of resistive switching and ferromagnetism modulation may provide a possible way to realize multi-state storage.