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Resistive switching in MoS2 embedded PVP composite-based ReRAM with Al and Ag electrodes is reported. A cost-free drop cast method was used to deposit active layers consisting of 30 wt%, 40 wt%, and 70 wt% of MoS2 in PVP. Each system exhibited unique electroforming and switching mode. Asymmetrical bipolar resistive switching occurring only in the positive voltage bias, a typical bipolar resistive switching and a typical ‘O-type’ resistive switching were observed for the 30 wt%, 40 wt%, and 70 wt% systems, respectively. Furthermore, injection of charge carriers at the electrode/active layer interface and electrochemical metalization mechanisms drove the formation of a nanoscale conductive filament in the device A and B. On the other hand, we attributed the conduction mechanism of device C to hopping conduction. Our results demonstrate the behaviour of MoS2 embedded PVP composite-based ReRAM has a strong dependence on the amount of MoS2 and that both the switching and conduction mechanism can be exploited by controlling the amount of MoS2 in the composite.

Low field microwave absorption (LFMA) in conducting polymers is completely different as compared to magnetic systems and is very intriguing. To understand LFMA phenomenon in the conducting polymers, we studied LFMA in the conducting polyaniline (PANI) polymer and iron nanoparticles (NPs) embedded polyaniline nanofibres (PANI-Fe) composite systems. PANI-Fe composite nanofibers were prepared by rapid mixing chemical polymerization of ANI monomer using FeCl3 as an oxidant and followed by the reduction of Fe2+/Fe3+ ions for the deposition of Fe NPs onto the PANI nanofibers matrix. Formation of PANI and deposition of Fe NPs were confirmed by HR-TEM, XRD and ATR-FTIR analyses, respectively. The study showed that in spite of PANI being non-degenerate conducting polymer, LFMA is absent in pure PANI. In contrary, LFMA signals are observed in Fe NPs embedded PANI nanofibers and bare Fe NPs systems. Presence of minor hysteresis in LFMA, as compared to the substantial magnetization hysteresis and the fact that LFMA derivative peaks not having any correlation with the M−H loop anisotropy and coercive fields rules out the conventional interpretation of LFMA arising from the low field spin magnetization processes as reported in the literature. Further it is perceived that microwave absorption in PANI-Fe system has a maximum at zero field and decreases with increasing applied magnetic field. This is totally in contradiction with the predicted behaviour of polaron-bipolaron based mechanism of LFMA origin, where the microwave absorption has a minimum at zero field and increases with the field in the case of non-degenerate conducting polymers, as reported in literature. However, LFMA correlates well with the magnetoresistance data for the PANI-Fe composite nanofibers system, indicating LFMA in this system is actually governed by magneto transport and not exactly by the low field magnetization process itself.

Defect induced room temperature ferromagnetism (RT-FM) in Ar+ implanted ZnO single crystal (ZnO-SC) is observe from the electron Spin Resonance (ESR) spectra and is correlated with their electronic structure studies using synchrotron radiation based X-ray absorption near edge structure (XANES) spectroscopy and valence band photoemission spectroscopy (VB-PES). Enhancement of absorption intensity at the edge of XANES spectra of Ar+ implanted ZnO indicates the increase of local density of states (DOS); which arises from the surface defects and/or dangling bonds in ZnO. VB-PES spectra change upon Ar+ implantation, becoming broader, implying the induced surface defects in ZnO-SC. X-ray photoelectron spectroscopy studies confirm that the Zn 2p3/2 core level peak shifts in lower energy side in Ar+ implanted ZnO-SC that is associated with the formation of oxygen vacancies/defects in ZnO-SC which is responsible for the RT-FM.

We studied the low-field microwave absorption (LFMA) in polycrystalline pellet and powdered (0.1–0.2 µm particle size) samples with a nominal composition of Zn1 − x(Mn:Fe(Ni))xO (x = 0.02). LFMA signals are stronger in the case of Mn:Fe co-doped ZnO, as compared to that of Mn:Ni co-doped ZnO. While the bulk samples show hysteresis, it disappears in the case of powdered samples. Further the line shapes of LFMA were modified with powdering, leading to small saturation fields for LFMA. This indicates that the microwave absorption in these powders is more sensitive than in the pellet form. We interpret these results in terms of interparticle–interfacial pinning. In this work, we clearly establish the low-field tunability of microwave absorption in the Zn1 − x(Mn:Fe(Ni))xO (x = 0.02) system, which is good for the applications as microwave absorbers with small field tunability as a functionality. This means LFMA can give inputs for the right choice of material for field-tunable microwave absorber design.

We report on the electron spin resonance (ESR) studies in the Mn:Ni and Mn:Gd co-doped ZnO system sintered at 500 and 800 °C. We found that sintering temperature has strong effect on the ESR line widths, with the Mn-Gd co-doped ZnO system showing the largest effect. Increasing sintering temperature has increased the line widths considerably, running into Kilo Oersted range. These large line widths indicate magnetic in-homogeneities and disorder and are consistent with the occurrence of secondary phases due to high-temperature sintering. Further analysing the asymmetry parameters, together with Δg/ g-values, we explain the weak ferromagnetism at low temperatures in 500°C sintered Mn:Gd-ZnO system to be due to spin canting which is the parasitic or the ‘spin-canted magnetism’. The ESR line intensity which is the spin susceptibility shows a paramagnetic behaviour in the range 300–100 K and shows a sharp rise and a peak around 40 K consistent with the magnetization data reported earlier. In the case of Mn:Ni–ZnO system, the Δg/ g and P asc parameters, which are proportional to spin canting and magneto-crystalline anisotropy, closely follow each other representing the classic picture of Moriya-Dzyaloshinsky.

The correlation of electronic structure and magnetic behaviors of layered molybdenum disulfide (MoS

This paper presents the conduction mechanisms and the observation of bipolar resistive switching in nano silver incorporated gelatin (AgG) composite films. Different concentrations of commercially purchased silver nanoparticles (0.3 w/v%, 0.5 w/v%, 0.7 w/v%) were incorporated in gelatin and AgG films were spin-coated on ITO substrates. We did systematic study of I- V characteristics in these films. The film with 0.5 w/v% exhibits an abrupt increase in current at 6 V with ON/OFF ratio of more than 3 orders of magnitude. Further, the I- V characteristics revealed O-type hysteresis behaviour along with hopping type of conduction for higher nano particle concentrations of 0.5 and 0.7w/v%. However, for much dilute concentration of Ag (0.3 w/v%), the conduction is of ohmic type

Tunability of key length scales including nanodimensionality, mean free path, localization length, and cyclotron radius gives opportunities to fabricate nanodevices with new functionalities. Herein, in order to tune localization length, composite nanorods (CNRs) of 2-naphthalene sulfonic acid doped polyaniline (PANI-NSA) and nickel ferrite nanoparticles (NiFe2O4 NPs) are synthesized via an in situ chemical polymerization method. The nanorods’ structure and the incorporation of the NiFe2O4 NPs into the PANI-NSA matrix are envisaged by various characterization techniques. The presence of a hysteresis loop with minor coercivity and remanence suggests the ferrimagnetic property of PANI-NSA/NiFe2O4 CNRs at room temperature. Investigation of electrical resistivity as a function of temperature in the absence of an external magnetic field establishes quasi-one-dimensional variable range hopping conduction mechanism of the PANI-NSA/NiFe2O4 CNR samples. CNR samples with two different loadings of NiFe2O4 NPs demonstrate substantial amounts of magnetoresistance (MR) at all the temperatures (300–50 K) studied. Intriguingly, a transition from positive to negative MR is observed with an increase in temperature from 200 to 300 K for CNR samples with less amount of NiFe2O4 (CNRs 1), whereas MR is positive for CNRs with higher loading of NiFe2O4, throughout the studied temperatures. Positive and negative MR behaviors of the CNR samples are quantitatively elucidated in terms of wave function shrinkage and forward interference models. Deduced localization length from the forward interference regime for CNRs 1 is about one order of magnitude larger than that in the wave function shrinkage regime. Thus, tuning of localization length can be achieved qualitatively through appropriate loading of NiFe2O4 NPs.Tunability of key length scales including nanodimensionality, mean free path, localization length, and cyclotron radius gives opportunities to fabricate nanodevices with new functionalities. Herein, in order to tune localization length, composite nanorods (CNRs) of 2-naphthalene sulfonic acid doped polyaniline (PANI-NSA) and nickel ferrite nanoparticles (NiFe2O4 NPs) are synthesized via an in situ chemical polymerization method. The nanorods’ structure and the incorporation of the NiFe2O4 NPs into the PANI-NSA matrix are envisaged by various characterization techniques. The presence of a hysteresis loop with minor coercivity and remanence suggests the ferrimagnetic property of PANI-NSA/NiFe2O4 CNRs at room temperature. Investigation of electrical resistivity as a function of temperature in the absence of an external magnetic field establishes quasi-one-dimensional variable range hopping conduction mechanism of the PANI-NSA/NiFe2O4 CNR samples. CNR samples with two different loadings of NiFe2O4 NPs demonst...

Copyright: 2019 IOP Science. Due to copyright restrictions, the attached PDF file contains the abstract version of the full-text item. For access to the full-text item, please consult the publisher's website. The definitive version of the work is published in the Journal of Physics D: Applied Physics, Vol 52(34), pp. 1-12

The correlation of electronic structure and magnetic behaviors of layered molybdenum disulfide (MoS2) nanosheets, mechanically exfoliated from pristine hexagonal crystal (2H-MoS2) have been studied. Raman spectra show the energy difference (ΔE) between two Raman peaks A 1g and [Formula: see text] was about 20.2 cm-1, indicating the formation of mono-/bi-layered MoS 2 nanosheets as obtained after mechanical exfoliation from pristine 2H-MoS 2 . The absence of the reflection peak (0 0 2) in x-ray diffraction patterns confirms the formation of few-layered and mono-/bi-layered MoS 2 nanosheets with reduced thickness. Mo 3d and S 2p XPS core level peaks shifted to higher energy with the reduction of the number of layers in exfoliated MoS2. As the number of layers decreased, valence band maximum position increased from 1.11 eV (pristine MoS2) to 1.57 eV (mono-/bi-layered MoS 2 nanosheets), whereas the surface work function (Ф) reduced from 4.85 eV (pristine MoS2) to 4.47 eV (mono-/bi-layered MoS2 nanosheets), as observed from UPS (He-I) measurements. UPS (He-II) spectra, as well as VB-PES spectra of mono-/bi-layered MoS 2 nanosheets, exhibits an enhanced valence band density of states (DOS) of S 3p -derived states near Fermi level (E f). Mo L II-edge and S K-edge x-ray absorption near edge structure spectra of mono-/bi-layered MoS 2 nanosheets show the splitting of different peaks that cause a noticeable change in their band structure. Magnetic M-H hysteresis loops measurement clearly demonstrates the increase of room temperature ferromagnetism from pristine to mono-/bi-layer MoS2, due to the existence of defects ('S'-vacancies or defects at the grain boundaries region) and the increase of DOS.

Polycrystalline bulk samples of Zn1-xMnxO with x=0.02, 0.04, 0.05 and sintered at different temperatures (500 °C & 800 °C) were studied to investigate the doping effect on the structural, optical properties and spin dynamics in ZnO system. The crystallite size was seen to decrease with no significant change in other structural parameters. FTIR study showed a small effect on the Zn-O stretching bond and other bonds due to presence of Mn. Calculation from UV-Vis spectra showed increase in the optical band gap in the low temperature sintered samples due to Mn doping. In the PL spectra, the UV emission seen to dominate for the 500 °C sintered sample, for 800 °C sample the visible emission dominate indicating increase in non-radiative emission. ESR signals obtained from the microwave absorption shows ferromagnetic signal for the low temperature sintered sample only with a g value of 2.004 for the 2% Mn doped sample. The number of spin participation for resonance is calculated from the ESR signal, which support...