Colossal Electroresistance Research Articles

Effects of Mn doping on electronic and quantum transport in PbPdO2 thin films.

PbPdO2, a gapless semiconductor, can be transformed into a spin gapless semiconductor structure by magnetic ion doping. This unique band-gap structure serves as the foundation for its distinctive physical properties. In this study, PbPd1-xMnxO2 (x = 0.05, 0.1, 0.15) thin films with (002) preferred orientation were prepared by laser pulse deposition (PLD). The structural, electroresistive and magnetoresistive properties were systematically characterized, and the results suggest that films with different Mn doping ratios exhibit a current-induced positive colossal electroresistance (CER), and the CER values of PbPd1-xMnxO2 thin films increase with the increase of Mn doping concentration. The CER values are several fold magnitudes higher compared to those of the previously reported PbPdO2 films possessing identical (002) orientation. Combined with first-principles calculation, the underlying influence mechanism of Mn doping on CER is elucidated. In situ X-ray photoelectron spectroscopy (XPS) demonstrates a close correlation between the positive CER and the band gap change induced by oxygen vacancies in PbPd1-xMnxO2. Additionally, it is observed that Mn-doped films exhibit weak localization (WL) and weak anti-localization (WAL) quantum transport. Moreover, it is found that Mn doping can lead to a transition from WAL to WL; a small amount of Mn doping significantly enhances the weak anti-localization effect. However, with increasing Mn concentration, the WAL effect is conversely weakened. The results of studies suggest strongly that PbPdO2, one of the few oxide topological insulators, can display novel quantum transport behavior by ion doping.

Effects of V and Gd doping on novel positive colossal electroresistance and quantum transport in PbPdO2 thin films with (002) preferred orientation.

In this work, PbPd0.9V0.1O2 and PbPd0.9Gd0.1O2 thin films with (002) preferred orientation were prepared using a pulsed laser deposition technique. The temperature dependence of resistivities ρI(T) was investigated under various applied DC currents. Colossal electroresistance (CER) effects were found in PbPd0.9V0.1O2 and PbPd0.9Gd0.1O2. It was found that the positive CER values of PbPd0.9V0.1O2 and PbPd0.9Gd0.1O2 reach 3816% and 154% for I = 1.00 μA at 10 K, respectively. In addition, the ρI(T) cycle curves of PbPd0.9V0.1O2 and PbPd0.9Gd0.1O2 thin films showed a critical temperature similar to that of PbPdO2 (Tc = 260 K). Particularly, charge transfer between O1- and O2- was confirmed by in situ XPS. Additionally, based on first-principles calculations and internal electric field models, the CER and magnetic sources in PbPd0.9V0.1O2 and PbPd0.9Gd0.1O2 can be well explained. Finally, it was found that thin film samples doped with V and G ions exhibit weak localization (WL) and weak anti-localization (WAL) quantum transport properties. Ion doping leads to a transition from WAL to WL. The study results indicate that PbPdO2, one of the few oxide topological insulators, can exhibit novel quantum transport behavior after ion doping.

Enormous electroresistance and field effect studies on LaMnO3–δ / La0.7Ca0.3MnO3 / LaAlO3 manganite – manganite composite structure

Field effect configuration (FEC) coupled field effect studies (FES) is one of the prime requisites for the development of spintronic based logic and memory devices having better sensitivities for external perturbations specifically while scaling down the technology. In this communication, LaMnO3–δ / La0.7Ca0.3MnO3 / LaAlO3 (LMO / LCMO / LAO) manganite – manganite composite structure was successfully fabricated using cost effective chemical solution deposition (CSD) method. FEC coupled FES have been performed across the electrically polarizable LMO layer and LCMO conducting channel. Enormous room temperature colossal electroresistance (CER) has been acquired ∼ 7000 % under 2 MV/cm forward biased control electric field and ∼ 8.5 × 105 % under 0.9 MV/cm reverse biased control electric field. Elegant modifications in the resistive behavior have been understood on the bases of charge carrier density alterations, interface modifications, phase separation, Mott–type phase transformation and formation–break down of depletion region across the manganite – manganite composite structure.

Preferred orientation in polycrystalline colossal electroresistive hollandite PbFexV6‐xO11

AbstractPreferred orientation in polycrystalline materials is one of the most challenging problems for structural analysis. Significant preferred orientation can severely affect the structure‐property analysis of the systems having substantial crystallographic anisotropy. Here, an extremely high degree of preferred orientation has been demonstrated in R‐block hollandite hexagonal PbFexV6−xO11 compounds, which has recently been shown to exhibit an unusual colossal electroresistance response that has a strong dependence on structural modifications. The present results warn against possible errors in understanding the evolution of the crystal structure of these hollandites, which might adversely affect the estimation of the influence of the same on their spectacular physical properties.

Colossal electroresistance response accompanied by metal-insulator transition in a mixed-valent vanadate

Colossal electroresistance (CER) in manganites, i.e., a large change in electrical resistance as a function of varying applied electric field or applied electric current, has often been described as complimentary to the colossal magnetoresistance (CMR) effect. Mixed valence vanadates with active ${t}_{2g}$ and empty ${e}_{g}$ orbitals, unlike manganites, have not naturally been discussed in this context, as double exchange based CMR is not realizable in them. However, presence of coupled spin and orbital degrees of freedom, metal-insulator transition (MIT) accompanied by orbital order-disorder transition, still make the vanadates important. Here we probe a Fe-doped hollandite lead vanadate $\mathrm{Pb}{\mathrm{Fe}}_{1.75}{\mathrm{V}}_{4.25}{\mathrm{O}}_{11}$ (PFVO), which exhibits a clear MIT as a function of temperature. Most importantly, a giant fall in the resistivity, indicative of a CER, as well as a systematic shift in the MIT towards higher temperatures are observed with increasing applied current. Detailed structural, magnetic, thermodynamic, and transport studies point towards a complex interplay between the structural distortion, orbital order/disorder effect, and the resultant MIT and magnetic ordering in this system.

The novel positive colossal electroresistance in PbPdO2 thin film with (002) preferred orientation

Doped PbPdO2 materials have attracted much attention as a spin gapless semiconductor (SGS) with the important properties of colossal electroresistance (CER) and giant magnetoresistance (GMR). In this study, the PbPdO2 thin films with (002) preferred orientation were prepared by pulsed laser deposition (PLD), and the temperature dependences of resistance and resistivity, R (T) and ρI (T), were measured under different applied DC currents. Remarkably, a positive CER effect induced by the current was firstly observed in the PbPdO2 films. In particular, it is novelty found that the positive CER value of PbPdO2 with I = 10 μA and T = 10 K reached about 300%. Moreover, the cyclic ρI (T) curves were also measured for I = 0.01 and 10 μA going back and forth between 10 K and 400 K. The time dependences of ρt/ρ0 ratio with T = 100 K, 300 K, 400 K and I = 0.01 and 0.1 μA were also obtained. A critical temperature Tc with about T = 260 K for all applied currents was found. As T > Tc，the band gap of the film is enhanced by the combined effect of the temperature and current. At the same time, Pb and O vacancies, and the evolution of oxygen valence states in the PbPdO2 film were observed by energy dispersive spectrometer (EDS), electron paramagnetic resonance (EPR) and in-situ x-ray photoelectron spectroscopy (XPS). Especially, the charge transport between O1− and O2− was confirmed by in-situ XPS. Finally, based on first-principles calculation, an internal electric field model and its induced potential barrier were established, which well explains the positive CER effect and the critical temperature Tc.

Impact of compressive and tensile epitaxial strain on transport and nonlinear optical properties of magnetoelectric BaTiO3-(LaCa)MnO3 tunnel junction

This work is devoted to disclosing the effect of epitaxial strain on crystallographic, transport, and nonlinear optical properties of a bilayer structure consisting of one ferroelectric (FE) (BaTiO3 with a thickness of 4 nm) and one ferromagnetic (La0.7Ca0.3MnO3 with the thickness of 12 nm) layers. Both tensile (of about ∼6% caused by the MgO substrate) and compressive (of about ∼1% caused by the SrTiO3 substrate) strains reduce the bulk metal-to-insulator phase transition temperature of the La0.7Ca0.3MnO3 layer from 240 K towards 195 K and 160 K, respectively. The appearance of the effect of colossal electroresistance, linear and nonlinear current–voltage behaviours and contribution of FE polarization switching in the BaTiO3 layer to the conductivity are associated with the influence of epitaxial strain. The predominance of the compressive over the tensile strain leads to the hysteresis behaviour of electroresistance, maximum conductivity caused by the resonant-tunnelling mechanism, and strong nonlinear optical dependence on the applied electric field.

Non-Ohmic conduction in exfoliated La0.7Ca0.3MnO3 thin films

We present a strong non-Ohmic transport characteristic of the exfoliated La0.7Ca0.3MnO3 thin film obtained by growing a water-soluble sacrificial layer of Sr3Al2O6 between the SrTiO3 substrate and the La0.7Ca0.3MnO3 film. The non-Ohmic conduction manifests itself as a significant amount of electroresistance over a wide range of temperatures. The resistance shows a plateaulike feature at low temperatures, and the electroresistance reaches ∼50 000% at 10 K for input currents varying from 1024 nA to 125 pA. The structural characterization of the exfoliated film reveals the existence of antiphase boundaries, the tunneling through which appears to cause the non-Ohmic feature. Our results provide an avenue into colossal tunneling electroresistance mediated by crystallographic defects.

Colossal Tunneling Electroresistance in Co‐Planar Polymer Ferroelectric Tunnel Junctions

AbstractFerroelectric tunnel junctions (FTJs) are ideal resistance‐switching devices due to their deterministic behavior and operation at low voltages. However, FTJs have remained mostly as a scientific curiosity due to three critical issues: lack of rectification in their current‐voltage characteristic, small tunneling electroresistance (TER) effect, and absence of a straightforward lithography‐based device fabrication method that would allow for their mass production. Co‐planar FTJs that are fabricated using wafer‐scale adhesion lithography technique are demonstrated, and a bi‐stable rectifying behavior with colossal TER approaching 106% at room temperature is exhibited. The FTJs are based on poly(vinylidenefluoride‐co‐trifluoroethylene) [P(VDF‐TrFE)], and employ asymmetric co‐planar metallic electrodes separated by <20 nm. The tunneling nature of the charge transport is corroborated using Simmons direct tunneling model. The present work is the first demonstration of functional FTJs manufactured via a scalable lithography‐based nano‐patterning technique and could pave the way to new and exciting memory device concepts.

Effect of aging on the current transport properties at gold/niobium-doped strontium titanate Schottky junctions

In this study, the effect of aging on current transport properties and the interface band structure of the Au/Nb-doped SrTiO3 (NSTO) junction was investigated. The as-fabricated Au/NSTO junctions showed extremely small rectification and exhibited rectifying current conduction and colossal electroresistance (CER) effect after exposure to air. In contrast, the Au/NSTO junctions kept in vacuum did not exhibit such aging behavior. Interestingly, the Au/NSTO junction capped with a Pt overlayer showed small rectification even after air exposure for one week. The changes in the potential profile with increasing air exposure time were assessed by X-ray photoemission techniques. The aforementioned time-dependent behaviors originated because of oxygen diffusion through the Au electrode, and it was found that oxygen stoichiometry at the electrode interface played an important role in the CER phenomena at the metal/NSTO junctions.

Electrically reversible cracks in an intermetallic film controlled by an electric field

Cracks in solid-state materials are typically irreversible. Here we report electrically reversible opening and closing of nanoscale cracks in an intermetallic thin film grown on a ferroelectric substrate driven by a small electric field (~0.83 kV/cm). Accordingly, a nonvolatile colossal electroresistance on–off ratio of more than 108 is measured across the cracks in the intermetallic film at room temperature. Cracks are easily formed with low-frequency voltage cycling and remain stable when the device is operated at high frequency, which offers intriguing potential for next-generation high-frequency memory applications. Moreover, endurance testing demonstrates that the opening and closing of such cracks can reach over 107 cycles under 10-μs pulses, without catastrophic failure of the film.

Electronic structure and its external electric field modulation of PbPdO2 ultrathin slabs with (002) and (211) preferred orientations

The Electronic structure of PbPdO2 with (002) and (211) preferred orientations were investigated using first-principles calculation. The calculated results indicate that, (002) and (211) orientations exhibit different electric field dependence of band-gap and carrier concentration. The small band gap and more sensitive electric field modulation of band gap were found in (002) orientation. Moreover, the electric field modulation of the resistivity up to 3–4 orders of magnitude is also observed in (002) slab, which reveals that origin of colossal electroresistance. Lastly, electric field modulation of band gap is well explained. This work should be significant for repeating the colossal electroresistance.

Resistive switching induced by charge trapping/detrapping: a unified mechanism for colossal electroresistance in certain Nb:SrTiO3-based heterojunctions

A unified mechanism for the colossal electroresistance effects in Nb:SrTiO3-based heterojunctions is revealed.

Estimation of Joule heating and its role in nonlinear electrical response of Tb 0.5 Sr 0.5 MnO 3 single crystal

Abstract Highly non-linear I–V characteristics and apparent colossal electro-resistance were observed in non-charge ordered manganite Tb 0.5 Sr 0.5 MnO 3 single crystal in low temperature transport measurements. Significant changes were noticed in top surface temperature of the sample as compared to its base while passing current at low temperature. By analyzing these variations, we realize that the change in surface temperature ( Δ T sur ) is too small to have caused by the strong negative differential resistance. A more accurate estimation of change in the sample temperature was made by back-calculating the sample temperature from the temperature variation of resistance (R–T) data ( Δ T cal ) , which was found to be higher than Δ T sur . This result indicates that there are large thermal gradients across the sample. The experimentally derived Δ T cal is validated with the help of a simple theoretical model and estimation of Joule heating. Pulse measurements realize substantial reduction in Joule heating. With decrease in sample thickness, Joule heating effect is found to be reduced. Our studies reveal that Joule heating plays a major role in the nonlinear electrical response of Tb0.5Sr0.5MnO3. By careful management of the duty cycle and pulse current I–V measurements, Joule heating can be mitigated to a large extent.

Dynamic strain enhanced abnormal percolative transport and colossal electroresistance in (011)-oriented La0.325Pr0.3Ca0.375MnO3/0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 heterostructure

Abnormal percolative transport properties have been studied in (011)-oriented La0.325Pr0.3Ca0.375MnO3 (LPCMO)/0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 (PMN-PT) heterostructure. By introducing a dynamic electric field-induced in-plane anisotropic strain-field in phase separated LPCMO film, we observed a significant promotion of the thermal hysteresis (∼68 K) and a positive colossal electroresistance (∼8450%). Such abnormal hysteresis is believed to be associated with anisotropic strain induced strong pinning effect in the material. This work unambiguously evidenced the importance of the anisotropic strain on the abnormal transport and meanwhile provides alternative opportunity for well understanding the percolation mechanism in inhomogeneous systems.

Direct observation of current-induced conductive path in colossal-electroresistance manganite thin films

Manganites are known to often show colossal electroresistance (CER) in addition to colossal magnetoresistance. The ${(\mathrm{L}{\mathrm{a}}_{1\ensuremath{-}y}\mathrm{P}{\mathrm{r}}_{y})}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{a}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ (LPCMO) system has a peculiar CER behavior in that little change of magnetization occurs. We use a magnetic force microscope to uncover the CER mechanism in the LPCMO system. In contrast to the previous belief that current reshapes the ferromagnetic metallic (FMM) domains, we show that the shape of the FMM domains remain virtually unchanged after passing electric current. Instead, it is the appearance of a tiny fraction of FMM ``bridges'' that is responsible for the CER behavior.

Current-voltage characteristics of manganite-titanite perovskite junctions.

After a general introduction into the Shockley theory of current voltage (J–V) characteristics of inorganic and organic semiconductor junctions of different bandwidth, we apply the Shockley theory-based, one diode model to a new type of perovskite junctions with polaronic charge carriers. In particular, we studied manganite–titanate p–n heterojunctions made of n-doped SrTi1−yNbyO3, y = 0.002 and p-doped Pr1−xCaxMnO3, x = 0.34 having a strongly correlated electron system. The diffusion length of the polaron carriers was analyzed by electron beam-induced current (EBIC) in a thin cross plane lamella of the junction. In the J–V characteristics, the polaronic nature of the charge carriers is exhibited mainly by the temperature dependence of the microscopic parameters, such as the hopping mobility of the series resistance and a colossal electro-resistance (CER) effect in the parallel resistance. We conclude that a modification of the Shockley equation incorporating voltage-dependent microscopic polaron parameters is required. Specifically, the voltage dependence of the reverse saturation current density is analyzed and interpreted as a voltage-dependent electron–polaron hole–polaron pair generation and separation at the interface.

Abnormal colossal electroresistance in Ru-doped La0.225Pr0.4Ca0.375MnO3

We investigate the magnetic and transport properties of polycrystalline bulk La0.225Pr0.4Ca0.375Mn1−xRuxO3 (x ≤ 0.15). With a slight Ru substitution of Mn, the Curie temperature of ferromagnetic transition is raised, the thermal hysteresis of resistivity is suppressed, and two metal-insulator transitions (MITs) coming from different mechanisms are observed. Furthermore, we observe that the resistivity of La0.225Pr0.4Ca0.375Mn1−xRuxO3 (0.01 ≤ x ≤ 0.1) increases abnormally with external electric field, and external magnetic field can suppress such abnormal electroresistance. These results suggest that the slight doping of Ru greatly suppresses the antiferromagnetic charge-ordered insulating (AFM/COI) phase. The Mn3+-Ru4+ ferromagnetic super-exchange and possible Ru4+-Ru4+ AFM interaction are implied to explain the observed behaviors.

Colossal Electroresistance and Resistive Switching in Manganite Based Heterostructures : A Review

Colossal Electroresistance and Resistive Switching in Manganite Based Heterostructures : A Review

Abnormal percolative transport and colossal electroresistance induced by anisotropic strain in (011)-Pr(0.7)(Ca(0.6)Sr(0.4))(0.3)MnO₃/PMN-PT heterostructure.

Abnormal percolative transport in inhomogeneous systems has drawn increasing interests due to its deviation from the conventional percolation picture. However, its nature is still ambiguous partly due to the difficulty in obtaining controllable abnormal percolative transport behaviors. Here, we report the first observation of electric-field-controlled abnormal percolative transport in (011)-Pr0.7(Ca0.6Sr0.4)0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructure. By introducing an electric-field-induced in-plane anisotropic strain-field in a phase separated PCSMO film, we stimulate a significant inverse thermal hysteresis (~ -17.5 K) and positive colossal electroresistance (~11460%), which is found to be crucially orientation-dependent and completely inconsistent with the well accepted conventional percolation picture. Further investigations reveal that such abnormal inverse hysteresis is strongly related to the preferential formation of ferromagnetic metallic domains caused by in-plane anisotropic strain-field. Meanwhile, it is found that the positive colossal electroresistance should be ascribed to the coactions between the anisotropic strain and the polarization effect from the poling of the substrate which leads to orientation and bias-polarity dependencies for the colossal electroresistance. This work unambiguously evidences the indispensable role of the anisotropic strain-field in driving the abnormal percolative transport and provides a new perspective for well understanding the percolation mechanism in inhomogeneous systems.