Field-induced Switching Research Articles

Mn doping-induced twofold spin reorientation and multi-step spin switching in NdFeO3 single crystal

Magnetization reversal and magnetic state regulation are the basis of application for magnetic materials in information processing. Here, twofold spin reorientation transitions (SRT) and field-induced multi-step spin switching phenomena were observed in NdMn0.2Fe0.8O3 (NMFO) single crystals grown via the optical floating zone method. Magnetic anisotropy was systematically investigated in both Zero-Field-Cooled (ZFC) and Field-Cooled (FC) modes. The NMFO single crystal exhibited twofold SRTs: from Γ4 (Gx, Ay, Fz) to Γ1 (Ax, Gy, Cz) and from Γ1 (Ax, Gy, Cz) to Γ2 (Fx, Cy, Gz). Furthermore, a magnetic field-induced spin reorientation transition was identified along the c-axis. Additionally, closer proximity to the SRT temperature corresponded to a reduced magnetic field requirement for inducing the spin reorientation transition. These findings contribute to our comprehension of spin dynamics in NMFO, presenting possibilities for future device applications.

Field-Induced Multistate Magnetization Switching in Ferromagnetic Nanowire with Parallel Anti-dots for Memristor Applications

Field-Induced Multistate Magnetization Switching in Ferromagnetic Nanowire with Parallel Anti-dots for Memristor Applications

Topological Quantum Switching Enabled Neuroelectronic Synaptic Modulators for Brain Computer Interface.

Aging and genetic-related disorders in the human brain lead to impairment of daily cognitive functions. Due to their neural synaptic complexity and the current limits of knowledge, reversing these disorders remains a substantial challenge for brain-computer interfaces (BCI). In this work, a solution is provided to potentially override aging and neurological disorder-related cognitive function loss in the human brain through the application of the authors' quantum synaptic device. To illustrate this point, a quantum topological insulator (QTI) Bi2Se2Te-based synaptic neuroelectronic device, where the electric field-induced tunable topological surface edge states and quantum switching properties make them a premier option for establishing artificial synaptic neuromodulation approaches, is designed and developed. Leveraging these unique quantum synaptic properties, the developed synaptic device provides the capability to neuromodulate distorted neural signals, leading to the reversal of age-related disorders via BCI. With the synaptic neuroelectronic characteristics of this device, excellent efficacy in treating cognitive neural dysfunctions through modulated neuromorphic stimuli is demonstrated. As a proof of concept, real-time neuromodulation of electroencephalogram (EEG) deduced distorted event-related potentials (ERP) is demonstrated by modulation of the synaptic device array.

Tuning the superconducting performance of YBa2Cu3O7-δ films through field-induced oxygen doping.

The exploration of metal-insulator transitions to produce field-induced reversible resistive switching effects has been a longstanding pursuit in materials science. Although the resistive switching effect in strongly correlated oxides is often associated with the creation or annihilation of oxygen vacancies, the underlying mechanisms behind this phenomenon are complex and, in many cases, still not clear. This study focuses on the analysis of the superconducting performance of cuprate YBa2Cu3O7-δ (YBCO) devices switched to different resistive states through gate voltage pulses. The goal is to evaluate the effect of field-induced oxygen diffusion on the magnetic field and angular dependence of the critical current density and identify the role of induced defects in the switching performance. Transition electron microscopy measurements indicate that field-induced transition to high resistance states occurs through the generation of YBa2Cu4O7 (Y124) intergrowths with a large amount of oxygen vacancies, in agreement with the obtained critical current density dependences. These results have significant implications for better understanding the mechanisms of field-induced oxygen doping in cuprate superconductors and their role on the superconducting performance.

Direct observation of intrinsic room-temperature ferroelectricity in 2D layered CuCrP2S6

Multiferroic materials have ignited enormous interest owing to their co-existence of ferroelectricity and ferromagnetism, which hold substantial promise for advanced device applications. However, the size effect, dangling bonds, and interface effect in traditional multiferroics severely hinder their potential in nanoscale device applications. Recent theoretical and experimental studies have evidenced the possibility of realizing two-dimensional (2D) multiferroicity in van der Waals (vdW) layered CuCrP2S6. However, the incorporation of magnetic Cr ions in the ferroelectric framework leads to antiferroelectric and antiferromagnetic orderings, while macroscopic spontaneous polarization is always absent. Herein, we report the direct observation of robust out-of-plane ferroelectricity in 2D vdW CuCrP2S6 at room temperature with a comprehensive investigation. Modification of the ferroelectric polarization states in 2D CuCrP2S6 nanoflakes is experimentally demonstrated. Moreover, external electric field-induced polarization switching and hysteresis loops are obtained in CuCrP2S6 down to ~2.6 nm (4 layers). By using atomically resolved scanning transmission electron microscopy, we unveil the origin of the emerged room-temperature ferroelectricity in 2D CuCrP2S6. Our work can facilitate the development of multifunctional nanodevices and provide important insights into the nature of ferroelectric ordering of this 2D vdW material.

Investigation on degree of non-ergodicity and local piezoelectric properties in Na0.5Bi0.5TiO3–BiFeO3–PbTiO3 system

Knowledge of the statics and dynamics of ferroelectric domains is of immense importance since they are directly correlated with macroscopic polarization and strain. For the present work, piezoresponse force microscopy (PFM) is used to afford insight into field-induced phase transitions and local switching properties of a (1–2x)Na0.5Bi0.5TiO3–xBiFeO3–xPbTiO3 system for compositions, x = 0.01, 0.03, 0.05, and 0.07. Rietveld analysis of x-ray diffraction data reveals crystallization of the compound in single and dual phases in the chosen compositions. Upon the application of a local electric field, a phase transition from relaxor to normal ferroelectric (FE) is observed for all samples. A decrease in degree of non-ergodicity is realized within this composition range, which is found by analyzing the stability of field-induced ferroelectric domains. The field-induced FE domains for lower concentrations of x are found to be irreversible and a reversible nature was found for higher values of x. In addition, spatial variations of local switching parameters are investigated with the help of switching spectroscopic-PFM and a maximum local d33 was found for compositions having dual phases.

Quantum Spin Hall States and Topological Phase Transition in Germanene.

We present the first experimental evidence of a topological phase transition in a monoelemental quantum spin Hall insulator. Particularly, we show that low-buckled epitaxial germanene is a quantum spin Hall insulator with a large bulk gap and robust metallic edges. Applying a critical perpendicular electric field closes the topological gap and makes germanene a Dirac semimetal. Increasing the electric field further results in the opening of a trivial gap and disappearance of the metallic edge states. This electric field-induced switching of the topological state and the sizable gap make germanene suitable for room-temperature topological field-effect transistors, which could revolutionize low-energy electronics.

Synergetic H-Bonding and C-T Interaction-Mediated Self-Assembled Structure Results in a Room-Temperature Ferroelectric Material Exhibiting Electric Field-Induced Dipole Switching and Piezo- and Pyroelectric Energy Conversion

Synergetic H-Bonding and C-T Interaction-Mediated Self-Assembled Structure Results in a Room-Temperature Ferroelectric Material Exhibiting Electric Field-Induced Dipole Switching and Piezo- and Pyroelectric Energy Conversion

Study and Simulation of the Electric Field-Induced Spin Switching in PZT/NiFe/CoFe Nanostructured Composites

In this work, we have studied the electric field-induced spin switching in the PZT/NiFe/CoFe nanostructured composites by sputtering ferromagnetic layers on a horizontal polarized piezoelectric PZT substrate. The electric field-induced change in the magnetization orientation was investigated systematically using a vibrating sample magnetometer and analytical simulations. The results revealed that electric field applications could indirectly control the magnetic spin orientations. Moreover, the magnetization change depends not only on the electric field but also on the direction of the electric field applying against the magnetic field. The images of magnetic moment orientations under various electric field applications are modeled by the Monte Carlo and NMAG simulations. In particular, a critical electric field of Ecr ≈ 300 kV/cm, which makes a 90o spin switching, was determined. These results are proposed to offer an opportunity for random access memory applications.

Reversible Entropy-Driven Defect Migration and Insulator-Metal Transition Suppression in VO2 Nanostructures for Phase-Change Electronic Switching.

Oxygen defects are among essential issues and required to be manipulated in correlated electronic oxides with insulator-metal transition (IMT). Besides, surface and interface control are necessary but challenging in field-induced electronic switching towards advanced IMT-triggered transistors and optical modulators. Herein, we demonstrated reversible entropy-driven oxygen defect migrations and reversible IMT suppression in vanadium dioxide (VO2 ) phase-change electronic switching. The initial IMT was suppressed with oxygen defects, which is caused by the entropy change during reversed surface oxygen ionosorption on the VO2 nanostructures. This IMT suppression is reversible and reverts when the adsorbed oxygen extracts electrons from the surface and heals defects again. The reversible IMT suppression observed in the VO2 nanobeam with M2 phase is accompanied by large variations in the IMT temperature. We also achieved irreversible and stable IMT by exploiting an Al2 O3 partition layer prepared by atomic layer deposition (ALD) to disrupt the entropy-driven defect migration. We expected that such reversible modulations would be helpful for understanding the origin of surface-driven IMT in correlated vanadium oxides, and constructing functional phase-change electronic and optical devices.

An Atomistic Model of Field-Induced Resistive Switching in Valence Change Memory

In valence change memory (VCM) cells, the conductance of an insulating switching layer is reversibly modulated by creating and redistributing point defects under an external field. Accurately simulating the switching dynamics of these devices can be difficult due to their typically disordered atomic structures and inhomogeneous arrangements of defects. To address this, we introduce an atomistic framework for modeling VCM cells. It combines a stochastic kinetic Monte Carlo approach for atomic rearrangement with a quantum transport scheme, both parametrized at the ab initio level by using inputs from density functional theory. Each of these steps operates directly on the underlying atomic structure. The model thus directly relates the energy landscape and electronic structure of the device to its switching characteristics. We apply this model to simulate field-induced nonvolatile switching between high- and low-resistance states in a TiN/HfO2/Ti/TiN stack and analyze both the kinetics and stochasticity of the conductance transitions. We also resolve the atomic nature of current flow resulting from the valence change mechanism, finding that conductive paths are formed between the undercoordinated Hf atoms neighboring oxygen vacancies. The model developed here can be applied to different material systems to evaluate their resistive switching potential, both for use as conventional memory cells and as neuromorphic computing primitives.

Metal-insulator transition and resistive switching in Y-doped CeO2 ceramics.

Y-doped ceria, Y0.16Ce0.84O1.92, is an oxide ion conductor that shows n-type conductivity under a small applied voltage. With increasing voltage, resistive switching by 2-3 orders of magnitude occurs that is reversible with some hysteresis and is enhanced in atmospheres of reduced pO2. The switching is a bulk effect, is not associated with Schottky barriers or with a crystallographic transition, occurs rapidly after a premonitory onset period depending on conditions and shows characteristics of a Mott transition. This is the third known example of low field-induced resistive switching in a bulk ceramic and represents an emergent phenomenon in materials that are taken outside their zone of thermodynamic stability.

Redox-active oxygen in oxides: emergent applications, including field-induced resistive switching, flash luminescence, p–n junctions and high capacity battery cathodes

Oxide ions are traditionally regarded as forming the inert anion sub-lattice of oxide structures whose properties are largely dominated by the cations present.

Resistive switching characteristics of W/TiO2/ITO devices

Materials with resistance-switching properties are proving to be promising for the novel non-volatile memories-resistive random-access memory (ReRAM). Despite extensive research on electric field-induced resistance switching, there are diverse opinions about its reliability and working mechanism. In this work, we analysed the impact of SET and RESET voltages on the switching characteristics and the possible current conduction mechanism of W/TiO2/ITO devices. By simple solution processing and spin coating, titanium dioxide thin films were grown on ITO, glass, silicon, and quartz substrates. The precursor and solvent used for the synthesis of the active layer were titanium isopropoxide and ethanol, respectively. Polycrystalline films with an anatase structure were formed after annealing at 400 °C with a 20 nm average crystallite size, as evidenced by X-ray diffraction patterns. The crystalline nature of the fabricated film has been found to improve on annealing. Using Raman spectroscopy, the chemical bonding states of the film were studied. A UV–visible spectrometer study confirms that anatase TiO2 possesses an indirect band gap transition with a 3.42 eV band gap. The device shows reversible, reproducible, stable, and bipolar resistance-switching behaviour as indicated by current–voltage (I-V) measurements, and it was found that there exists a minimum voltage (∼-4 V) to set the device into an ON state. Compared to crystalline TiO2, theamorphous active layer offers much better switching characteristics, such as good cyclic endurance with a Roff-Ronratio ∼ 10.The current–voltage characteristics were fitted to various carrier transport mechanismssuch as Ohmic conduction, Schottky emission (SE), Space-charge-limited conduction (SCLC), and Poole-Frenkel emission (PF). Among these, the ohmic and SE mechanisms were detected at low and high fields, respectively. Schottky barrier modulation at the metal-oxide interface has been identified as the motive for switching.

Ion Drift and Polarization in Thin SiO2 and HfO2 Layers Inserted in Silicon on Sapphire.

To reduce the built-in positive charge value at the silicon-on-sapphire (SOS) phase border obtained by bonding and a hydrogen transfer, thermal silicon oxide (SiO2) layers with a thickness of 50–310 nm and HfO2 layers with a thickness of 20 nm were inserted between silicon and sapphire by plasma-enhanced atomic layer deposition (PEALD). After high-temperature annealing at 1100 °C, these layers led to a hysteresis in the drain current–gate voltage curves and a field-induced switching of threshold voltage in the SOS pseudo-MOSFET. For the inserted SiO2 with a thickness of 310 nm, the transfer transistor characteristics measured in the temperature ranging from 25 to 300 °C demonstrated a triple increase in the hysteresis window with the increasing temperature. It was associated with the ion drift and the formation of electric dipoles at the silicon dioxide boundaries. A much slower increase in the window with temperature for the inserted HfO2 layer was explained by the dominant ferroelectric polarization switching in the inserted HfO2 layer. Thus, the experiments allowed for a separation of the effects of mobile ions and ferroelectric polarization on the observed transfer characteristics of hysteresis in structures of Si/HfO2/sapphire and Si/SiO2/sapphire.

Spin chirality induced large topological Hall effect in magnetic Weyl semimetallic Eu2Ir2O7 (111) thin films

Antiferromagnetic (AFM) pyrochlore iridates are a fertile ground to hunt for a Weyl semimetallic state characterized by a linear crossing of two nondegenerate bands near the Fermi level ${E}_{F}$. Here, we demonstrate evidence of low-temperature anomalous and topological Hall effects in an antiferromagnetic ${\mathrm{Eu}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$(111) epitaxial thin film. The observed anomalous Hall effect is explained in terms of the momentum space Berry curvature associated with the Weyl nodes in the electronic band structure. The topological Hall effect reaches a large value ${\ensuremath{\rho}}_{xy}^{\text{THE}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}10\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\text{cm}$ at 2 K. The topological nature of the Hall effect is attributed to the nonzero scalar spin chirality of the all-in-all-out/all-out-all-in (AIAO/AOAI) type noncoplanar AFM spin structure. The magnetoresistance (MR) shows a prominent negative variation ($\mathrm{MR}\ensuremath{\sim}10%$ at 2 K) below 10 K. The field dependence of MR below 5 K varies quadratically in the low-field regime, and above 40 kOe it shows a linear trend. The quadratic to linear crossover of the MR is explained by the field-induced ($H$) spin canting (spin chirality) of the static spins in the AIAO/AOAI spin structure. In the intermediate-temperature region MR of $15\ensuremath{-}25$ K exhibits a hysteretic response which is associated with field-induced domain switching of the AIAO/AOAI spin structure. This work highlights the interplay of magnetism and topology in a spin-orbit-coupled correlated electron system and unravels the possibility for realizing the Weyl phase in antiferromagnetic ${\mathrm{Eu}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$(111) thin films.

Angle-dependent switching in a magnetic tunnel junction containing a synthetic antiferromagnet

The angle dependence of field-induced switching was investigated in magnetic tunnel junctions with in-plane magnetization and a pinned synthetic antiferromagnet reference layer. The 60 × 90 nm2 elliptical nanopillars had sharp single switches when the field was applied along the major axis of the ellipse, but even with small (20°) deviations, reversal occurred through an intermediate state. The results are interpreted with a model that includes the external applied field and the effective fields due to shape anisotropy and the fringe field of the synthetic antiferromagnet and used to extract the magnetization direction at various points in the magnetoresistance loop. The implications for faster spintronic probabilistic computing devices are discussed.

Angle selective piezoelectric strain-controlled magnetization switching in artificial spin ice based multiferroic system

The prospect of electrically controlled writing of ferromagnetic bits is highly desirable for developing scalable and energy-efficient spintronics devices. In this direction, various efforts have been made to achieve electrically controlled magnetization switching utilizing an artificial multiferroic system. To date, the magnetization switching has been realized in a diverse nanopatterned magnetic system. However, the demonstration of electric field-induced strain-controlled magnetization switching in artificial spin ice (ASI) coupled with a piezoelectric material is still unexplored. In the present work, we perform micromagnetic simulations to investigate the electric field-induced strain-mediated magnetization switching in an ASI based multiferroic system. Here, the piezoelectric strain-controlled magnetization switching has been studied by applying the electric-field pulse at different angles with respect to the axes of the system. Remarkably, magnetization switches by 180° only if the external electric-field pulse is applied at some specific angles, close to the anisotropy axis of the system (≈30°–60°). Our detailed analysis of the demagnetization energy variation reveals that the energy barrier becomes antisymmetric in such cases, facilitating complete magnetization reversal. Moreover, we have also proposed a possible magnetization reversal mechanism with two sequential electric-field pulses of a relatively smaller magnitude. We believe that the present work could pave the way for a future ASI-based multiferroic system for scalable magnetic field-free low power spintronics devices.

Ferroelectric polarization reversal in multiferroic MnWO4 via a rotating magnetic field up to 52 T

A long-standing issue in multiferroic ${\mathrm{MnWO}}_{4}$ is the electric polarization reversal when magnetic field is applied along the magnetic easy axis $(H||u)$. In this work, we performed comprehensive ferroelectric polarization measurements on ${\mathrm{MnWO}}_{4}$ in fields up to 52 T and with rotating field direction in the $ac$ plane. When the field is rotated from $H||c$ to $H||u$, the induced high-field phase $(\ensuremath{-}P||b)$ favors a sign reversal relative to the low-field $+P||b$ phase, which is attributed to the vector spin chirality changing from one side of the spin connecting vector to the other. Particularly, further slight deviation of the field from the magnetic easy axis towards $H||a$ causes an abrupt reversal of the high-field phase from $\ensuremath{-}P||b$ to $+P||b$. We assume that this unusual angular dependence of polarization behavior can be understood by magnetic control of the helicity of the chiral plane with opposite conical spin structures. In addition, we also propose electric-field control of the chiral plane close to the ferroelectric phase transition at high fields. This study results in an overall understanding of this important multiferroic material and sheds light on field-induced polarization switching in related compounds.

In-situ X-ray absorption spectroscopy (XAS) studies of electrical field induced domain switching in BCZT ceramics

X-ray absorption spectroscopy (XAS) is one of the important technique to investigate the oxidation states, electronic structure, and local atomic structure, which are crucial parameters in ferroelectric ceramics. In this work, in-situ XAS and x-ray diffraction (XRD) techniques were employed to investigate the field-induced ferroelectric domain switching and Ti off-center displacement in Ba0·85Ca0·15Zr0·1Ti0·9O3 ceramics. Ferroelectric BCZT ceramics possess an excellent ferroelectric property, but their mechanism of field-induced ferroelectricity is still unclear. The present work demonstrates that in-situ XAS can be applied to quantify field induced octahedral distortion (Ti off-center displacement) and provide a better understanding of the origin of ferroelectric properties in BCZT ceramics.