arXiv subjects

P. Levy

Publications and source records attributed to P. Levy.

At least 19 recordsLinked to original sources

arXiv2021

Proton irradiation effects on metal-YBCO interfaces

10 MeV proton-irradiation effects on a YBCO-based test structure were analyzed by measuring its current-voltage (IV) characteristics for different cumulated fluences. For fluences of up to $\sim$80$\cdot$10$^9$~p/cm$^2$ no changes in the electrical behavior of the device were observed, while for a fluence of $\sim$~300$\cdot$10$^9~$ p/cm$^2$ it becomes less conducting. A detailed analysis of the room temperature IV characteristics based on the $\gamma$ power exponent parameter [$\gamma=dLn(I)/dLn(V)$] allowed us to reveal the main conduction mechanisms as well as to establish the equivalent circuit model of the device. The changes produced in the electrical behavior, in accordance with Monte Carlo TRIM simulations, suggest that the main effect induced by protons is the displacement of oxygen atoms within the YBCO lattice, particularly from oxygen-rich to oxygen-poor areas, where they become trapped.

cond-mat.mtrl-sci↗

arXiv2020

LabOSat as a versatile payload for small satellites: first 100days in LEO orbit

In this work the first results obtained by LabOSat-01 platform are presented. This platform was designed for testing custom devices on board of small satellites. Two LabOSat-01 type boards were launched and placed into Low Earth Orbit (LEO) on May 30, 2016. We present here an analysis of data collected by one of these boards during the first days of mission. Total Ionization Dose results are compared with data acquired by LabOSat-01`s predecessor board, MeMOSat-01, launched in 2014.

physics.ins-det↗

arXiv2020

YBCO-based non-volatile ReRAM tested in Low Earth Orbit

An YBCO-based test structure corresponding to the family of ReRAM devices associated with the valence change mechanism is presented. We have characterized its electrical response previous to its lift-off to a Low Earth Orbit (LEO) using standard electronics and also with the dedicated LabOSat-01 controller. Similar results were obtained in both cases. After about 200 days at LEO on board a small satellite, electrical tests started on the memory device using the LabOSat-01 controller. We discuss the results of the first 150 tests, performed along a 433-day time interval in space. The memory device remained operational despite the hostile conditions that involved launching, lift-off vibrations, permanent thermal cycling and exposure to ionizing radiation, with doses 3 orders of magnitude greater than the usual ones on Earth. The device showed resistive switching and IV characteristics similar to those measured on Earth, although with changes that follow a smooth drift in time. A detailed study of the electrical transport mechanisms, based on previous models that indicate the existence of various conducting mechanisms through the metal-YBCO interface showed that the observed drift can be associated with a local temperature drift at the LabOSat controller, with no clear evidence that allows determining changes in the underlying microscopic factors. These results show the reliability of complex-oxide non-volatile ReRAM-based devices in order to operate under all the hostile conditions encountered in space-borne applications.

physics.app-ph↗

arXiv2016

Origin of multistate resistive switching in Ti/manganite/Si$O_x$/Si heterostructures

We report on the growth and characterization of Ti/$La_{1/3}$$Ca_{2/3}$Mn$O_3$/Si$O_x$/n-Si memristive devices. We demonstrate that using current as electrical stimulus unveils an intermediate resistance state, in addition to the usual high and low resistance states that are observed in standard voltage controlled experiments. Based on thorough electrical characterization (impedance spectroscopy, current-voltage curves analysis), we disclose the contribution of three different microscopic regions of the device to the transport properties: an ohmic incomplete metallic filament, a thin manganite layer below the filament tip exhibiting Poole-Frenkel like conduction, and the SiOx layer with an electrical response well characterized by a Child-Langmuir law. Our results suggest that the existence of the SiOx layer plays a key role in the stabilization of the intermediate resistance level, indicating that the combination of two or more active RS oxides adds functionalities in relation to single-oxide devices. We understand that these multilevel devices are interesting and promising as their fabrication procedure is rather simple and they are fully compatible with standard Si-based electronics.

cond-mat.mtrl-sci↗

arXiv2016

Manganite-based three level memristive devices with self-healing capability

We report on non-volatile memory devices based on multifunctional manganites. The electric field induced resistive switching of Ti/$La_{1/3}$$Ca_{2/3}$Mn$O_3$/n-Si devices is explored using different measurement protocols. We show that using current as the electrical stimulus (instead of standard voltage-controlled protocols) improves the electrical performance of our devices and unveils an intermediate resistance state. We observe three discrete resistance levels (low, intermediate and high), which can be set either by the application of current-voltage ramps or by means of single pulses. These states exhibit retention and endurance capabilities exceeding $10^4$ s and 70 cycles, respectively. We rationalize our experimental observations by proposing a mixed scenario were a metallic filament and a Si$O_x$ layer coexist, accounting for the observed resistive switching. Overall electrode area dependence and temperature dependent resistance measurements support our scenario. After device failure takes place, the system can be turned functional again by heating up to low temperature (120 C), a feature that could be exploited for the design of memristive devices with self-healing functionality. These results give insight into the existence of multiple resistive switching mechanisms in manganite-based memristive systems and provide strategies for controlling them.

cond-mat.mtrl-sci↗

arXiv2014

Correlation between electrical and magnetic properties of phase separated manganites studied with a General Effective Medium model

We have performed electrical resistivity and DC magnetization measurements as a function of temperature, on polycrystalline samples of phase separated LaPrCaMnO. We have used the General Effective Medium Theory to obtain theoretical resistivity vs. temperature curves corresponding to different fixed ferromagnetic volume fraction values, assuming that the sample is a mixture of typical metallic like and insulating manganites. By comparing this data with our experimental resistivity curves we have obtained the relative ferromagnetic volume fraction of our sample as a function of temperature. This result matches with the corresponding magnetization data in excellent agreement, showing that a mixed phase scenario is the key element to explain both the magnetic and transport properties in the present compound.

cond-mat.mtrl-sci↗

arXiv2013

Non-volatile multilevel resistive switching memory cell: A transition metal oxide-based circuit

We study the resistive switching (RS) mechanism as way to obtain multi-level memory cell (MLC) devices. In a MLC more than one bit of information can be stored in each cell. Here we identify one of the main conceptual difficulties that prevented the implementation of RS-based MLCs. We present a method to overcome these difficulties and to implement a 6-bit MLC device with a manganite-based RS device. This is done by precisely setting the remnant resistance of the RS-device to an arbitrary value. Our MLC system demonstrates that transition metal oxide non-volatile memories may compete with the currently available MLCs.

cond-mat.other↗

arXiv2011

Asymmetric pulsing for reliable operation of titanium/manganite memristors

We present a pulsing protocol that significantly increases the endurance of a titanium-manganite interface used as a binary memory cell. The core of this protocol is an algorithm that searches for the proper values for the set and reset pulses, canceling the drift in the resistance values. A set of experiments show the drift-free operation for more than $10^{5}$ switching cycles, as well as the detrimental effect by changing the amplitude of pulses indicated by the protocol. We reproduced the results with a numerical model, which provides information on the dynamics of the oxygen vacancies during the switching cycles.

cond-mat.mtrl-sci↗

arXiv2010

Hysteresis Switching Loops in Ag-manganite memristive interfaces

Multilevel resistance states in silver-manganite interfaces are studied both experimentally and through a realistic model that includes as a main ingredient the oxygen vacancies diffusion under applied electric fields. The switching threshold and amplitude studied through Hysteresis Switching Loops are found to depend critically on the initial state. The associated vacancy profiles further unveil the prominent role of the effective electric field acting at the interfaces. While experimental results validate main assumptions of the model, the simulations allow to disentangle the microscopic mechanisms behind the resistive switching in metal-transition metal oxide interfaces.

cond-mat.other↗

arXiv2010

Mechanism for bipolar resistive switching in transition metal oxides

We introduce a model that accounts for the bipolar resistive switching phenomenom observed in transition metal oxides. It qualitatively describes the electric field-enhanced migration of oxygen vacancies at the nano-scale. The numerical study of the model predicts that strong electric fields develop in the highly resistive dielectric-electrode interfaces, leading to a spatially inhomogeneous oxygen vacancies distribution and a concomitant resistive switching effect. The theoretical results qualitatively reproduce non-trivial resistance hysteresis experiments that we also report, providing key validation to our model.

cond-mat.mtrl-sci↗

arXiv2006

Large domain wall resistance in self-organised manganite film

The electrical resistance of magnetic domain walls in ferromagnetic metallic manganites can be enhanced to 10-12 Ohm.m2 by patterning nanoconstrictions [J. Appl. Phys. 89, 6955 (2001)]. We show equally large enhancements in a phase separated La0.60Ca0.40MnO3 manganite film without recourse to nanopatterning. The domain walls were measured in the current-perpendicular-to-the-plane (CPP) geometry between ferromagnetic metallic La0.70Ca0.30MnO3 electrodes patterned like magnetic tunnel junctions.

cond-mat.mtrl-sci↗

arXiv2006

High resolution determination of ferromagnetic metallic limit in epitaxial La1-xCaxMnO3 films on NdGaO3

The physical properties of manganites depend strongly on sample morphology, probably due to strain. We investigate the influence of NdGaO3 substrates on the limit of the ferromagnetic-metallic phase field in La1-xCaxMnO3, doping with x=1% resolution. Films with x=0.40 show a metal-insulator transition, but the ferromagnetic volume fraction is half the spin aligned value. Films with x=0.41 are similar but the metal-insulator transition is not always seen. Films with x=0.42, 0.43, 0.44, 0.45 are insulating, and the magnetization is dramatically reduced. The observed phase boundary indicates where to search for enhanced phase separation effects that may be exploited in thin films and devices.

cond-mat.mtrl-sci↗

arXiv2006

Evidences of a consolute critical point in the Phase Separation regime of La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single crystals

We report on DC and pulsed electric field sensitivity of the resistance of mixed valent Mn oxide based La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single crystals as a function of temperature. The low temperature regime of the resistivity is highly current and voltage dependent. An irreversible transition from high (HR) to a low resistivity (LR) is obtained upon the increase of the electric field up to a temperature dependent critical value (V_c). The current-voltage characteristics in the LR regime as well as the lack of a variation in the magnetization response when V_c is reached indicate the formation of a non-single connected filamentary conducting path. The temperature dependence of V_c indicates the existence of a consolute point where the conducting and insulating phases produce a critical behavior as a consequence of their separation.

cond-mat.str-el↗

arXiv2005

Decoupled magnetic and electrical switching in manganite trilayer

We report magnetic and electrical transport studies of an epitaxially grown trilayer thin film structure comprising La0.59Ca0.41MnO3 sandwiched between La0.67Ca0.33MnO3 electrodes. Since La0.59Ca0.41MnO3 lies at the edge of the thin film ferromagnetic metallic phase field, phase separation effects are expected. These effects can explain the observed magnetic isotropy of the middle layer. By contrast, the electrode material is magnetically uniaxial. Easy axis magnetic field sweeps of the trilayer produce two sharp magnetic transitions, but only one sharp transition in current-in-plane resistance measurements.

cond-mat.mtrl-sci↗

arXiv2005

The electrical current effect in phase separated La5/8-yPryCa3/8MnO3: Charge order melting vs. Joule heating

We have studied the effect of electric field on transport properties of the prototypical phase separated manganite La5/8-yPryCa3/8MnO3 with y=0.34. Our results show that the suggested image in which the charge ordered state is melted by the appliance of an electric current and/or voltage has to be revised. We were able to explain the observed resistivity drop in terms of an artifact related to Joule heating and the particular hysteresis that the system under study display, common to many other phase separated manganites.

cond-mat.str-el↗

arXiv2005

Simultaneous electric and magnetic field induced nonvolatile memory

We investigate the electric field induced resistive switching effect and magnetic field induced fraction enlargement on a polycrystalline sample of a colossal magnetoresistive compound displaying intrinsic phase coexistence. Our data show that the electric effect (presumably related to the presence of inhomogeinities) is present in a broad temperature range(300 to 20 K), being observable even in a mostly homogeneous ferromagnetic state. In the temperature range in which low magnetic field determines the phase coexistence fraction, both effects, though related to different mechanisms, are found to determine multilevel nonvolatile memory capabilities simultaneously.

cond-mat.str-el↗

arXiv2004

Magnetoresistive memory in phase separated La$_{0.5}$Ca$_{0.5}$MnO$_{3}$

We have studied a non volatile memory effect in the mixed valent compound La$_{0.5}$Ca$_{0.5}$MnO$_{3}$ induced by magnetic field (H). In a previous work [R.S. Freitas et al., Phys. Rev. B 65 (2002) 104403], it has been shown that the response of this system upon application of H strongly depends on the temperature range, related to three well differentiated regimes of phase separation occurring below 220 K. In this work we compare memory capabilities of the compound, determined following two different experimental procedures for applying H, namely zero field cooling and field cooling the sample. These results are analyzed and discussed within the scenario of phase separation.

cond-mat.mtrl-sci↗

arXiv2004

Abrupt field-induced transition triggered by magnetocaloric effect in phase-separated manganites

The occurrence at low temperatures of an ultrasharp field-induced transition in phase separated manganites is analyzed. Experimental results show that magnetization and specific heat step-like transitions below 5 K are correlated with an abrupt change of the sample temperature, which happens at a certain critical field. This temperature rise, a magnetocaloric effect, is interpreted as produced by the released energy at the transition point, and is the key to understand the existence of the abrupt field-induced transition. A qualitative analysis of the results suggests the existence of a critical growing rate of the ferromagnetic phase, beyond which an avalanche effect is triggered.

cond-mat.mtrl-sci↗