Abstract
We report on the magnetic field control of a bipolar resistive switching in Ag/TiO
2
/FTO based resistive random access memory device through I–V characteristics. Essentially, in the ...presence of magnetic field and in the low resistance state, an abrupt change in the resistance of the device demands higher voltage, hinting that residual Lorentz force plays a significant role in controlling the resistance state. Endurance characteristics of the device infer that there is no degradation of the device even after repeated cycling, which ensures that the switching of resistance between ‘off’ and ‘on’ states is reproducible, reversible and controllable. Magnetic field control of ‘on’ and ‘off’ states in endurance characteristics suggest that this device can be controlled in a remote way for multi-bit data storage.
Abstract
Bio – molecules detection and their quantification with a high precision is essential in modern era of medical diagnostics. In this context, the memristor device which can change its ...resistance state is a promising technique to sense the bio - molecules. In this work, detection of the Bovine Serum Albumin (BSA) protein using resistive switching memristors based on TiO
2
and TiO
2
+ graphene oxide (GO) is explored. The sensitivity of BSA detection is found to be 4 mg/mL. Both the devices show an excellent bipolar resistive switching with an on/off ratio of 73 and 100 respectively, which essentially demonstrates that the device with GO, distinguishes the resistance states with a high precision. The enhanced performance in the GO inserted device (~ 650 cycles) is attributed to the prevention of multi-dimensional and random growth of conductive paths.
We report on the temperature dependent Raman scattering studies of polycrystalline HoCr1 − xFexO3 (x = 0 and 0.5) compounds. No signature of phonon mode related to structural phase transition is ...evident in the investigated temperature range in both the compounds. The thermal evolution of phonon spectra indicates a deviation of B3g(3) mode from the expected anharmonic behaviour below magnetic ordering temperature TN in HoCrO3 compound. This behaviour is attributed to spin–phonon coupling, which is due to the modulation of super exchange integral by lattice vibration. On the other hand, the anomalous behaviour of Ag mode and its line‐width around magnetic ordering in HoCr0.5Fe0.5O3 compound suggest the spin–phonon coupling. Apart from that, a clear deviation of wavenumber pertinent to B2g(1) mode suggests the possibility to observe ferroelectricity in HoCr0.5Fe0.5O3 compound. We believe that the present results would be helpful in obtaining new materials with multiferroicity near room temperature.
We report on the temperature dependent Raman spectroscopy studies of polycrystalline HoCr1 − xFexO3 (x = 0 and 0.5) compounds. Observed spin‐phonon coupling in x = 0 compound is attributed to the deviation of B3g(3) mode from the expected anharmonic behaviour; on the other hand, it is correlated to anomalous behaviour of Ag mode and its line‐width around magnetic ordering in x = 0.5 compound.
Two types of graphene nanoribbons: (a) potassium-split graphene nanoribbons (GNRs), and (b) oxidative unzipped and chemically converted graphene nanoribbons (CCGNRs) were investigated for their ...magnetic properties using the combination of static magnetization and electron spin resonance measurements. The two types of ribbons possess remarkably different magnetic properties. While a low-temperature ferromagnet-like feature is observed in both types of ribbons, such room-temperature feature persists only in potassium-split ribbons. The GNRs show negative exchange bias, but the CCGNRs exhibit a “positive exchange bias”. Electron spin resonance measurements suggest that the carbon-related defects may be responsible for the observed magnetic behavior in both types of ribbons. Furthermore, information on the proton hyperfine coupling strength has been obtained from hyperfine sublevel correlation experiments performed on the GNRs. Electron spin resonance finds no evidence for the presence of potassium (cluster) related signals, pointing to the intrinsic magnetic nature of the ribbons. Our combined experimental results may indicate the coexistence of ferromagnetic clusters with antiferromagnetic regions leading to disordered magnetic phase. We discuss the possible origin of the observed contrast in the magnetic behaviors of the two types of ribbons studied.
We report on the first-order reversal curves (FORC) of magnetization and effect of defects on magnetization process in Fe71Ga29 thin films with different values of sputtering power (50 – 120 W). ...Phase purity of the thin films was confirmed by grazing incidence X– ray diffraction (GI-XRD). The reversible and irreversible contributions to the magnetization are evidenced through the minor loop parameter such as pseudo hysteresis loss (WF*) and energy loss coefficient (WF0). In particular, the energy loss coefficient is found to decrease from 28 × 106 (A/m. mT) at 50 W to 21 × 106 (A/m. mT) at 120 W, which signifies a decrease in domain wall resistance. FORC infers narrow switching, which leads to low coercivity distribution at 120 W as a result of less defects.
•Uniaxial anisotropy, pseudo magnetic properties in Fe2NiGe Heusler alloy thin films.•The crest height and trough depth coefficients are 9.44 × 106 (A/m).mT and 8.76 × 106 (A/m).mT respectively.•FORC ...infers small switching field distribution and formation of vortex state.
We report on the anisotropy, pseudo magnetic properties and formation of vortex state in Fe2NiGe thin films. From the torque measurements, estimated anisotropy constants K1 and K2 are found to be 4.47 × 103 J/m3 and −1.98 × 102 J/m3 respectively. Pseudo magnetic properties such as pseudo hysteresis work and pseudo remanence work infer that motion of domain wall in Fe2NiGe is rather smooth. The crest height and trough depth coefficient from the second stage of magnetization curves are estimated and are found to be 9.44 × 106 (A/m).mT and 8.76 × 106 (A/m).mT respectively. First order reversal curves infer switching field distribution is very small, which infers that less dislocations and more grain size. Indeed, the vortex state is evident from the contour graph of the first order reversal curves. We believe present results would be helpful for the future spintronic devices based on Heusler alloy thin films.
•Enhanced efficiency of TiO2 DSSC by demagnetization fields.•Enhanced recombination time due to stray fields.•Evidence for stray fields using magnetic force microscopy and micromagnetic ...simulations.•Realization of more absorption of the light through transfer matrix modelling.
We report on the effect of demagnetizing fields due to magnetite (Fe3O4) nanoparticles (NPs) on the efficiency of TiO2 based dye sensitized solar cells (DSSC). The addition of Fe3O4 NPs into the photoanode enhanced the power conversion efficiency of DSSC. This may be attributed to the magnetic field effect induced by the demagnetizing field produced by the magnetite NPs, which is evident from our micromagnetic simulation. Essentially, such a stray field would induce additional force on the electron motion and thereby enhancing the recombination time of these charge carriers. Enhancement in recombination time is directly evidenced by the increase in short circuit current density. In addition, we have carried out an electrochemical impedance spectroscopy (EIS) study to probe the mechanism of charge transport within the DSSC device. Quenching of intensity in phosphorescence data indeed infer a decrease in recombination rate. We calculated the value of demagnetization energy from NPs with micromagnetic simulations. Absorbed energy density of ‘s’ and ‘p’ polarized incident light estimated using transfer matrix model.
We report on the effect of low substrate temperature on the correlation between structure, magnetic properties, and micromagnetic behavior of Fe 70 Ga 30 thin films. The enhanced grain size and the ...decrease in the number of pinning centers are in correlation with the enhanced saturation magnetization and domain size (~0.2-<inline-formula> <tex-math notation="LaTeX">0.5~\mu \text{m} </tex-math></inline-formula>), respectively. Estimated effective magnetic anisotropy energy (<inline-formula> <tex-math notation="LaTeX">K_{\mathrm {eff}} </tex-math></inline-formula>) is found to increase with substrate temperature from <inline-formula> <tex-math notation="LaTeX">7.5 \times 10^{5} </tex-math></inline-formula> J/m 3 (room temperature) to <inline-formula> <tex-math notation="LaTeX">13.6 \times 10^{5} </tex-math></inline-formula> J/m 3 (350 °C). The coercivity variation from the object-oriented micromagnetic framework (OOMMF) simulation is in line with respect to experimental values. Spin structure from simulation also indicates multiple-domain configuration when there is a magnetization reversal.
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