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A ferroelectric PVDF-based flexible triboelectric nanogenerator (TENG) has been fabricated to analyze the effect of ambient temperature on the electrical outputs. The open-circuit voltage increased from 6.2 to 20 V with the increase in the ambient temperature up to 41 °C. However, beyond 41 °C, the electrical outputs start decreasing. Through tuning the ambient temperature, an ∼11-fold enhancement in the output power density of the TENG was achieved. In order to investigate the mechanism behind the temperature-tuned TENG outputs, the temperature-dependent dielectric permittivity and conductivity of the film have been studied. The dielectric permittivity and conductivity of the films are observed to increase with the temperature. The increase in the dielectric permittivity has been attributed to the PVDF segmental chains' movements, causing the enhancement in dielectric permittivity, which results in more surface charge and improvements in the TENG electrical outputs. However, a large increment in film conductivity at higher temperatures causes the leakage of surface charges, resulting in a decrement in TENG outputs. Furthermore, the temperature-dependent performance of PVDF-CdS nanocomposite-based TENG has also been investigated and found to enhance the performance from 8 to 27 V with the increase in temperature from 33 to 41 °C. The additional interfacial polarization between CdS nanoparticles and the PVDF matrix and higher ferroelectricity in nanocomposites contribute to larger TENG outputs of the PVDF/CdS nanocomposite-based TENG device. [ABSTRACT FROM AUTHOR]

Non-volatile, multilevel bipolar Resistive Switching (RS) along with multilevel magnetization switching, in a cobalt ferrite (CFO) thin film using a simple Cu/CFO/Pt sandwich structure, has been demonstrated. Besides the low resistance state (LRS) and the high resistance state (HRS), the device exhibits two intermediate resistance states (IRSs), which are stable with time and reproducible in RS cycles. The endurance characteristics of the present RS device (>500 switching cycles) show no noticeable degradation and the ultimate resistance ratio always remains >104, which ensures reproducibility, reversibility, and controllability of the RS features of the present device. The HRS of the device shows a semiconducting conduction mechanism, whereas the LRS and both the IRSs were found to be Ohmic in nature. Simultaneous magnetization and resistive switching confirmed the multifunctional behavior of the device and suggested the presence of a valence change mechanism of resistive switching. The magnetization vs. magnetic field studies and temperature dependent resistance studies revealed that the electrochemical metallization also plays an important role during the switching process, which enhances the resistance ratio by providing an additional metallic filament of Cu atoms along with the ionic conducting filament of oxygen vacancies. The voltage controlled multilevel magnetization and resistive switching with a large memory window (resistance ratio >104) make the present device a potential candidate for paving the path for future multifunctional and multilevel memory devices with the capability of high density data storage. [ABSTRACT FROM AUTHOR]

In this letter, a compact spur-line based magnetically tunable bandstop filter in the flip-chip configuration using partially magnetized ferrite thin films is reported. The spur-line bandstop filter is designed to operate at a centre frequency of ~12.75 GHz and is fabricated on a quartz substrate. Magnetic thin films of cobalt ferrite, cobalt-nickel ferrite, and nickel ferrite are used, which show tunabilities of 5.1%, 6.0%, and 7.5%, respectively, after applying the bias magnetic field ranging from 0 to 300 Oe. The difference in the tunability is attributed to the change in the permeability values of the magnetic thin films after applying the bias magnetic field. The shift in the centre frequency is confirmed by the simulations carried out using CST microwave studio software. This work demonstrates the opportunities to use the partially magnetized ferrite thin films in the presence of a low bias magnetic field for achieving higher tunability in a microwave bandstop filter. [ABSTRACT FROM AUTHOR]

Single phase CoFe2O4 thin films are deposited on quartz substrates at 400 °C using ultrasonic assisted chemical vapor deposition, and the tuning of optical bandgap and saturation magnetization of films is demonstrated by varying the post deposition annealing temperature. The optical band gap varies from 1.58 to 1.41 eV and saturation magnetization increases from 4 to 46 emu/g as the post deposition annealing temperature is increased from 500 °C to 700 °C. The observed change in optical bandgap and the magnetic properties is attributed of the shifting of Co2+ from the octahedral to the tetrahedral site with the increase in the annealing temperature. Raman studies of the films support the redistribution of Co2+ among the octahedral and tetrahedral sites in CoFe2O4 films with the increase in the annealing temperature. [ABSTRACT FROM AUTHOR]

Flexible piezoelectric nanogenerator (PENG) using a poly(vinylidene fluoride)–cobalt ferrite (PVDF–CFO) nanocomposite film is prepared in which the output power of the PENG device can be tuned by the application of an external magnetic field. Ferromagnetic CFO nanoparticles were prepared by the hydrothermal method and are incorporated in the PVDF matrix using the drop casting technique. The presence of CFO in the PVDF matrix enhances the ferroelectric β phase fraction of PVDF from 59% to 75% and also provides magnetic tunability to the PENG device. With the application of a 2.1 kG field, there is 2.33 times increment in instantaneous output power of the PENG, which is attributed to a decrease in the resistance of the nanocomposite film due to the alignment of the magnetic moment of CFO nanoparticles leading to a reduction in the scattering of mobile charges. These outcomes open up a possibility in piezomagnetotronic materials through the realization of magneto-sensitive multifunctional PENGs, which can be scaled up for fabricating compact, high-performance, portable devices for smart sensor applications. [ABSTRACT FROM AUTHOR]

Magnetic flux noise in MgB2 polycrystalline sample is measured using a high-TC rf-superconducting quantum interference device in the temperature range of 6–40 K. A small magnetic field (∼200 mG) was applied while cooling the sample. The flux noise exhibits 1/fα type of behavior with α∼1.0–1.3 and shows enhanced noise around 24 and 37 K. The flux noise seems to originate from thermally activated vortex hopping. The large magnetic noise at 24 K indicates the presence of larger density of pinning sites with energies ∼0.061 eV leading to enhanced magnetic fluctuations at temperatures much below TC. [ABSTRACT FROM AUTHOR]

We investigated conduction through an artificial grain-boundary junction made in La[sup 0.67]Ba[sup 0.33]MnO[sub 3] thin films, deposited on a 36.7° SrTiO[sub 3] bicrystal substrate using a laser ablation technique. The grain boundary exhibits substantial magnetoresistance at low temperatures and also shows nonlinear I - V characteristics. Analysis of temperature dependence of the dynamic conductance allows us to identify three carrier transport mechanisms across the grain boundary. These mechanisms exist in parallel, and at a given temperature one mechanism may dominate. Particularly, at higher temperatures (T > 175 K) the transport across the grain boundary involves spin-flip scattering, which we establish leads to decrease of the bicrystal grain-boundary contribution in magnetoresistance. At lower temperature (4.2-45 K), tunneling through a disordered oxide at the grain boundary dominates, whereas in the temperature range from 100 to 175 K, carrier transport is dominated by inelastic tunneling via pairs of manganese atoms. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators are devices that can transform mechanical energy into electrical energy, and regulating their performance is critical for energy harvesting applications and other applications where they act as sensors. In the present work, we have fabricated a ferroelectric PVDF-NaNbO3 nanocomposite film-based triboelectric nanogenerator and demonstrated a large tuning (64%) of the output of the triboelectric nanogenerator by adjusting its electrical polarization state. The triboelectric nanogenerator fabricated using a negatively polarized PVDF-NaNbO3 nanocomposite film has an instantaneous output power of 0.17 mW, which is significantly higher than the triboelectric nanogenerator fabricated using a positively polarized PVDF-NaNbO3 nanocomposite film, which has an output power of 0.06 mW. Kelvin probe force microscopy measurements were carried out to explore the cause of the change in the output with the change in the polarization state of the films. The work function of the PVDF-NaNbO3 film is found to change with the polarization of the film, which resulted in the change in the output. More explanation of the effect of the polarization state on the performance of the triboelectric nanogenerator has been presented using an electronic energy level diagram of the contacting materials. The current work demonstrated the advantage of using ferroelectric polymers for triboelectric nanogenerator applications, because the output performance of the triboelectric nanogenerator can be tuned as per requirement. [ABSTRACT FROM AUTHOR]

Studies radio frequency superconducting quantum interference device (SQUID) effects due to natural grain-boundary junctions in ErNi[sub 2]B[sub 2]C and DyNi[sub 2]B[sub 2]C magnetic borocarbide superconductors. Amplitude of voltage-flux SQUID modulations; Occurrence of magnetic ordering; Flux noise density of the SQUID.

We report the observation of radio frequency-superconducting quantum interference device (rf-SQUID) effect due to natural grain boundary weak links in a bulk sample of a YNi2B2C superconductor at 4.2 K, confirming that the superconducting grains are coupled at the grain boundaries through Josephson effect. Periodic oscillations in voltage-flux characteristic due to rf-SQUID effect have been clearly observed at 4.2 K when the driving rf frequency was kept slightly away from the resonance frequency of the tank circuit. Phase reversal in the voltage-flux characteristics on changing the rf frequency has been observed. Noise spectrum of the YNi2B2C bulk rf-SQUID is also reported. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines the operation of bicrystal junction high-temperature direct current-SQUID in a portable microcooler. Use of a modulation signal in SQUID operation; Importance of SQUID noise characterization in a liquid nitrogen Dewar to evaluate the performance in the microcooler; Similarities between Dewar and microcooler performance.

Controlled bipolar resistive switching (BRS) has been observed in nanostructured CoFe2O4 (CFO) films using an Al (aluminum)/CoFe2O4/FTO (fluorine-doped tin oxide) device. The fabricated device shows electroforming-free uniform BRS with two clearly distinguished and stable resistance states without any application of compliance current, with a resistance ratio of the high resistance state (HRS) and the low resistance state (LRS) of >102. Small switching voltage (<1 volt) and lower current in both the resistance states confirm the fabrication of a low power consumption device. In the LRS, the conduction mechanism was found to be Ohmic in nature, while the high-resistance state (HRS/OFF state) was governed by the space charge-limited conduction mechanism, which indicates the presence of an interfacial layer with an imperfect microstructure near the top Al/CFO interface. The device shows nonvolatile behavior with good endurance properties, an acceptable resistance ratio, uniform resistive switching due to stable, less random filament formation/rupture, and a control over the resistive switching properties by choosing different stop voltages, which makes the device suitable for its application in future nonvolatile resistive random access memory. [ABSTRACT FROM AUTHOR]

The effect of magnetic CoFe2O4 (CFO) nanofillers on the thermoelectric properties of the Bi2Te3–CFO nanocomposite is investigated, and their role in the enhancement of thermoelectric properties is demonstrated. In the presence of a small magnetic field (25 mT), the electrical conductivity is enhanced by 16% and, simultaneously, the Seebeck coefficient is enhanced by 23%. The presence of CFO nanoparticles in the matrix of Bi2Te3 in the nanocomposite produces an interpenetrating network of the magnetically induced orientation of the magnetic moment of CFO, which results in the substantial reduction in the interface barrier by suppressing scattering of charge carriers at the interfaces. The simultaneous enhancement in the electrical conductivity and Seebeck coefficient in the presence of the small magnetic field resulted in an ∼52% enhancement of figure of merit for the Bi2Te3–CFO (4 wt. %) nanocomposite. [ABSTRACT FROM AUTHOR]