Colossal Electroresistance Research Articles

Electric and magnetic modulation of fully strained dead layers inLa0.67Sr0.33MnO3films

We report the electrical transport and magnetic properties of the dead layer of La(0.67)Sr(0.33)MnO(3) grown on LaAlO(3) substrate under the influence of magnetic field and electric voltage. The electrical resistance of the dead layer shows exponential decrease with both magnetic field and electric voltage, leading to colossal magnetoresistance and electroresistance, respectively. However, the sample cannot be driven into a metallic state with the available magnetic field and electric voltage. At low temperatures, the magnetic-field dependence of both magnetization and resistance show remarkable hysteresis. Exchange bias effect was observed in the magnetization vs magnetic-field curves. Magnetic force microscope measurement reveals the coexistence of different magnetic phases in the dead layer. The results were discussed in terms of phase separation in the dead layer. This work demonstrates the presence of phase separation in the manganite dead layer and its tunability by magnetic field and electric voltage.

Fabrication and Characterization of Colossal Electroresistance Chip Devices Composed of Polycrystalline Lanthanum‐Doped Strontium Titanate and Palladium Electrodes

A colossal electroresistance (CER) multilayered chip device composed of polycrystalline 0.8‐at% La‐doped SrTiO3 and Pd electrodes has been successfully fabricated. Polycrystalline SrTiO3 devices exhibit large hysteresis in their current–voltage (I–V) characteristics after the forming process. Further, their resistance states can be switched by applying voltage pulses above ±50 V, and the resistance changes by approximately two orders of magnitude (from ∼600 Ω to ∼80 kΩ). These resistance‐switching behaviors demonstrate that even ceramics can exhibit resistance changes as large as thin‐film devices and provide the possibility of new switching devices with the memory effect composed of ceramics.

Microstructure dependence of the electroresistance of Nd0.7Sr0.3MnO3

Nd0.7Sr0.3MnO3 ceramics of perovskite-type were respectively prepared by solid-state reaction and high-energy ball milling with post heating-treatment. The samples obtained using these methods show a great of difference in electrical transport despite having the same crystallographic structure, similar grain size and chemical composition. For the sample prepared by solid-state reaction, the electrical resistance keeps unchanged with current loads and no electroresistance effect takes place. However, for the sample prepared by high-energy ball milling with post heating treatment, the electrical resistance decreases remarkably with increasing current loads and shows colossal electroresistance effect. The microstructure of materials, in particular the screw dislocation-like structure, is supposed to be responsible for the difference in electrical transport.

Colossal electroresistance and electron instability in strongly correlated electron systems

Studies of the electron instability effects (EIEs) in structures based in strongly correlated electron systems (SCESs), such as high-temperature superconductors (HTSCs) and doped manganites (compounds with colossal magnetoresistance), are reviewed. These effects manifest themselves in achange of several orders of magnitude in the resistive state of the normal metal–HTSC or normal metal–DM (doped manganite) interface in an electric field under significant currentinjection conditions. The results of studying HTSC- and doped-manganite-based heterojunctions are considered. EIEs in heterostructures are compared with the electric field effect on the properties of an SCES in thin fllms and gate-containing devices. The general features and distinctions in the physics of these ðhenomena are analyzed.

Dielectrophoresis model for the colossal electroresistance of phase-separated manganites

We propose a dielectrophoresis model for phase-separated manganites. Without increase of the fraction of metallic phase, an insulator-metal transition occurs when a uniform electric field applied across the system exceeds a threshold value. Driven by the dielectrophoretic force, the metallic clusters reconfigure themselves into stripes along the direction of electric field, leading to the filamentous percolation. This process, which is time dependent, irreversible, and anisotropic, is a probable origin of the colossal electroresistance in manganites.

Colossal electroresistance in the ferromagnetic insulating state of single crystalNd0.7Pb0.3MnO3

Colossal electroresistance (CER) has been observed in the ferromagnetic insulating (FMI) state of a manganite. Notably, the CER in the FMI state occurs in the absence of magnetoresistance (MR). Measurements of electroresistance (ER) and current induced resistivity switching have been performed in the ferromagnetic insulating state of a single crystal manganite of composition Nd$_0.7$Pb$_0.3$MnO$_3$ (NPMO30). The sample has a paramagnetic to ferromagnetic (Curie) transition temperature, Tc = 150 K and the ferromagnetic insulating state is realized for temperatures, T <~ 130 K. The colossal electroresistance, arising from a strongly nonlinear dependence of resistivity ($\rho$) on current density (j), attains a large value ($\approx 100%$) in the ferromagnetic insulating state. The severity of this nonlinear behavior of resistivity at high current densities is progressively enhanced with decreasing temperature, resulting ultimately, in a regime of negative differential resistivity (NDR, d$\rho$/dj < 0) for temperatures <~ 25 K. Concomitant with the build-up of the ER however, is a collapse of the MR to a small value (< 20%) even in magnetic field, H = 7 T. This demonstrates that the mechanisms that give rise to ER and MR are effectively decoupled in the ferromagnetic insulating phase of manganites. We establish that, the behavior of ferromagnetic insulating phase is distinct from the ferromagnetic metallic (FMM) phase as well as the charge ordered insulating (COI) phase, which are the two commonly realized ground state phases of manganites.

Frequency dependence of the resistive switching effect in Bi 2Sr 2CaCu 2O 8+ y/Ag film heterocontacts

In this work we have performed the relaxation studies “ in situ” of the electron instability effect (EIE) in the heterostructures based on BSCCO single crystals. The new effect of suppression of EIE or colossal electroresistance via application of an alternating low frequency electric field to the heterojunctions in the BSCCO-based single crystals has been found. It has been shown that the top possible frequencies for observation of the effect are of the order of 10 3 Hz. This fact is interpreted as accumulation of the oxygen ions driven by the electric field to the interface. On the other hand, it has been shown that the switching events are limited by two time processes: t ≈ 1 ms and about ten seconds. The first ones are caused by rearrangement of a charge net in the degraded surface at the electric field switching. The latter are caused by oxygen diffusion to vacancies under electric field above some threshold value. The considered experimental data confirm the correlation character of the HTSC properties as Mott systems, which appears in extreme sensitivity to the doping level, in the tendency to phase separation under external actions, in the hysteresis character of the metal–insulator transition.

Electric field induced collapse of the charge-ordered phase in manganites

The colossal electroresistance in manganites accompanies the insulator-to-metal phasetransition induced by the electric field. A phenomenological phase transition model isproposed to study this electric field induced collapse of the charge-ordered phase. Thehysteresis of the phase transition is well explained using the effective mediumapproximation. The volume fraction of the metallic region at the metal-to-insulatortransition point is estimated as 30%.

Colossal electroresistance without colossal magnetoresistance in La0.9Sr0.1MnO3

The authors report on colossal electroresistance (ER) in the ferromagnetic insulator manganite La0.9Sr0.1MnO3. The single crystal samples exhibit a transition into a low resistive state above a certain threshold current. Pulsed measurements demonstrate that this transition is not a consequence of heating. ER behaves similarly to magnetoresistance (MR) above the orbital order temperature TOO. Below TOO the MR is only 20% while ER enhances the conductivity by several orders of magnitude. Magnetic field and electric current have opposite effects on the conductivity, therefore, it seems that only the injected carriers are able to modify the ordering of eg Mn orbitals.

Electrical properties and colossal electroresistance of heteroepitaxialSrRuO3∕SrTi1−xNbxO3(0.0002⩽x⩽0.02)Schottky junctions

We investigated the electrical properties of heteroepitaxial oxide Schottky junctions, $\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_{3}∕\mathrm{Sr}{\mathrm{Ti}}_{1\ensuremath{-}x}{\mathrm{Nb}}_{x}{\mathrm{O}}_{3}$ $(0.0002\ensuremath{\leqslant}x\ensuremath{\leqslant}0.02)$. The overall features agree with those of a conventional semiconductor Schottky junction, as exemplified by the rectifying current $(I)$-voltage $(V)$ characteristics with linear $\mathrm{log}\phantom{\rule{0.2em}{0ex}}I\text{\ensuremath{-}}V$ relationship under forward bias and the capacitance $(C)\text{\ensuremath{-}}V$ characteristics with linear $1∕{C}^{2}\text{\ensuremath{-}}V$ relationship under reverse bias. The $x$ dependence of the junction parameters, such as barrier height, built-in potential, and depletion layer width, can be analyzed by taking into account the band-gap narrowing due to degeneration, as well as the bias-dependent dielectric constant of depleted $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$. All junctions, except for the most heavily doped $(x=0.02)$ one, show hysteretic $I\text{\ensuremath{-}}V$ characteristics with a colossal electroresistance (CER) effect, where forward (reverse) bias stress reduces (enhances) the junction resistance. The $x$ dependence of the CER effect and the absence of hysteresis in the $C\text{\ensuremath{-}}V$ relationship suggest that the resistance switching in Schottky junctions comes from the change in conductance through additional tunneling paths rather than the change in barrier potential profile. Electron charging in or discharging from a self-trap depending on the bias polarity may account for the nonvolatility of the CER effect. This model is supported by the fact that the CER effect is completely suppressed in interface-engineered junctions with a $\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_{3}∕2\text{\ensuremath{-}}\mathrm{nm}$-thick $X∕\mathrm{Sr}{\mathrm{Ti}}_{0.99}{\mathrm{Nb}}_{0.01}{\mathrm{O}}_{3}$ structure, where $X$ is either pristine $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ or very heavily electron-doped ${\mathrm{La}}_{0.25}{\mathrm{Sr}}_{0.75}\mathrm{Ti}{\mathrm{O}}_{3}$.

Novel approaches to field modulation of electronic and magnetic properties of oxides

The interplay of electronic charge and spin in many of the novel multicomponent oxides presents opportunities for new device concepts. In this paper we summarize three different approaches to making field-modulated devices. The first is the observation of a giant electroresistance (ER) effect in the colossal magnetoresistive manganites, where it is shown that in the same system two phenomena operate, colossal magnetoresistance (CMR) and colossal electroresistance (CER) and both processes are complementary. In the second example we show the modulation of the magnetic property of a diluted magnetic semiconductor by an electric field but the role of unidentified ferromagnetic entities cannot be ruled out at this stage. In the third and last case we show the example of the multiferroic materials where the magnetic properties are field dependent as well, but for totally different reasons.

Effect of oxygen annealing on Pr0.7Ca0.3MnO3 thin film for colossal electroresistance at room temperature

We studied an appropriate annealing condition of Pr0.7Ca0.3MnO3 (PCMO) thin film that can show good resistive switching characteristics for resistance random access memory applications and also tried to elucidate the mechanism of the resistive switching of PCMO thin film at room temperature. We could observe that crystal structure of PCMO film was changed by oxygen annealing. From x-ray photoelectron spectroscopy measurements, we can conclude that the excess of oxygen by oxygen annealing of PCMO film leads to an increase of Mn4+ content at the PCMO surface with a subsequent change in the Mn4+∕Mn3+ ratio at the PCMO surface. The resistance ratio of high resistance state and low resistance state was increased by oxygen annealing of PCMO thin film. This can be explained as follows. The change of the Mn4+∕Mn3+ ratio at the PCMO surface by oxygen annealing leads to the change of characteristics of Au-PCMO interface domain and therefore results in the change of the resistance ratio.

Enhanced colossal electroresistance in Cu/Pr0.7Ca0.3MnO3/Cu structure

Voltage-current (V-I) curves have been measured in symmetrical metal/Pr0.7Ca0.3MnO3/metal structures with metal=Ag, Cu, Pt, and Au. Our four measured samples exhibit room-temperature nonlinear and asymmetric V-I curves with electrical hysteresis loops. Among these four samples, Cu/Pr0.7Ca0.3MnO3/Cu produces the largest hysteresis loop, yielding an enhanced colossal electroresistance of 2279% at a current of 0.5 A.

Colossal electroresistance and current induced switching in ferromagnetic insulating state of La0.82Ca0.18MnO3

Colossal electroresistance and current induced resistivity switching have been measured in the ferromagnetic insulating (FMI) state of single crystal manganite La0.82Ca0.18MnO3. The sample has a Curie transition temperature TC=165K and the FMI state is realized for temperatures T&amp;lt;100K. The electroresistance (ER), arising from a strong nonlinear resistivity, attains a large value (≈100%) in the FMI state. However, this is accompanied by a collapse of the magnetoresistance (MR) to a small value even in magnetic field (H) of 10T. This demonstrates that the mechanisms that give rise to ER and MR are effectively decoupled.

Nonvolatile multivalued memory effects in electronic phase-change manganites controlled by Joule heating

Non-volatile multivalued memory effects caused by magnetic fields, currents, and voltage pulses are studied in Nd_{0.65}Ca_{0.35}MnO_3 and (Nd_{1-y}Sm_{y})_{0.5}Sr_{0.5}MnO_3 (y=0.75) single crystals in the hysteretic region between ferromagnetic metallic and charge-ordered insulating states. The current/voltage effects observed in this study are explained by the self-heating effect, which enable us to control the colossal electroresistance effects. This thermal-cycle induced switching between electronic solid and liquid states can be regarded as electronic version of atomic crystal/amorphous transitions in phase-change chalcogenides.

Colossal electroresistance and low-field colossal magnetoresistance in the single-crystal bilayered manganiteLa1.2Sr1.8Mn2O7

We report the observation of current-induced abrupt transition from a metallic to an insulating state in a bilayered manganite ${\mathrm{La}}_{1.2}{\mathrm{Sr}}_{1.8}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ single crystal. A colossal electroresistance effect $[\ensuremath{\rho}(50\phantom{\rule{0.3em}{0ex}}\mathrm{mA})\ensuremath{-}\ensuremath{\rho}(1\phantom{\rule{0.3em}{0ex}}\mathrm{mA})]∕\ensuremath{\rho}(50\phantom{\rule{0.3em}{0ex}}\mathrm{mA})=93%$ is found at $120\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Moreover, the current-induced transition is very sensitive to external magnetic fields. At the measuring current of $50\phantom{\rule{0.3em}{0ex}}\mathrm{mA}$ a low-field colossal magnetoresistance effect, $[\ensuremath{\rho}(H)\ensuremath{-}\ensuremath{\rho}(0)]∕\ensuremath{\rho}(0)=\ensuremath{-}86%$, occurs at $H=500\phantom{\rule{0.3em}{0ex}}\mathrm{Oe}$. This low-field magnetoresistance effect can be repeatedly modulated by external magnetic field. We interpret these phenomena as the consequence of the percolative conduction and local Joule thermal effect.

Interfaces of Correlated Electron Systems: Proposed Mechanism for Colossal Electroresistance

Mott's metal-insulator transition at an interface due to band bending is studied by the density matrix renormalization group approach. We show that the result can be recovered by a simple modification of the conventional Poisson's equation approach used in semiconductor heterojunctions. A novel mechanism of colossal electroresistance is proposed, which incorporates the hysteretic behavior of the transition in higher dimensions.

Controllable colossal electroresistance inLa0.8Ca0.2MnO3epitaxial thin films

We observed a significant enhancement of electric resistivity excited by a dc current in ${\mathrm{La}}_{0.8}{\mathrm{Ca}}_{0.2}{\mathrm{MnO}}_{3}$ epitaxial thin films. Such an enhanced resistance can be achieved when the applied dc current exceeds a threshold value. It also strongly depends on the duration of the dc current excitation. The induced enhancement in resistance can be well controlled by varying the duration of the current excitation. More attractive is that the enhanced resistance is extremely sensitive to weak currents. Even a very small dc current can remarkably depress the induced resistance, showing a colossal electroresistance (ER) in a very wide temperature range, even to room temperature. The maximum of ER can reach $\ensuremath{\sim}1350%$ for temperatures lower than $\ensuremath{\sim}50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $\ensuremath{\sim}580%$ even at 300 K when the current changes from 0.7 to 10 $\ensuremath{\mu}\mathrm{A}$. Structure measurements on a microarea by the micrometer x-ray diffraction technique were carried out. No change of the structure and lattice parameter was found upon current treatments. Phase separation is taken into account in the interpretation of the observed phenomena.

Current-induced colossal electroresistance in p-n heterostructure of La0.67Ca0.33MnO3−δ and Nb-doped SrTiO3

We report the colossal negative electroresistance (ER) in the p-n heterostructure of La0.67Ca0.33MnO3−δ (LCMO) and Nb-doped SrTiO3. For a vacuum-annealed sample, a maximum ER of 4×104% can be reached by 1 mA current and magnetic field has remarkable influence on the ER of the sample. It is interesting that the magnetoresistance of the heterostructure can also be tuned by electric current. The results were explained by the current shunting model. In this scenario, the current shunting is determined by the resistance of LCMO and the junction resistance. On the other hand, the resistance of LCMO and the junction resistance are also affected by current. The interaction of these factors can tune the electrical transport of the heterostructure dramatically. This work shows that manganites combined with other materials can result in some interesting properties that may have potential applications.

Current-sensitive electroresistance and the response to a magnetic field in La0.8Ca0.2MnO3 epitaxial thin films

The influence of a transport dc current on the resistivity of La0.8Ca0.2MnO3 epitaxial thin films and their response to a magnetic field has been investigated. We found that when the applied dc current exceeds a threshold value, the electric resistivity in these films could be significantly enhanced. Such observations are completely repeatable. More attractive is that the enhanced resistance turns out to be sensitive to a weak current in a wide temperature range from 10 to 300 K. Even a very small dc current could remarkably depress the high resistance, showing a colossal electroresistance (ER) effect. ER reaches ∼1175% at temperatures lower than ∼50K, and ∼705% at 300 K for a current changing from 0.72 to 10.5 μA. A highly nonlinear behavior of the I–V curves persists even to room temperature. Significant influence of the magnetic field on the electric transports was also observed. It is found that a low field of 0.25 T could remarkably affect the I–V curves, resulting in a considerable magnetoresistance (MR).