Jitendra Pal Singh

EPR STUDY OF NANOSTRUCTURED ZINC FERRITE

Bulk zinc ferrite has been studied in the past. In the bulk form zinc ferrite crystallizes in the normal spinel structure with all the zinc ions occupying the tetrahedral and all the iron occupying the octahedral sites, respectively. But, nanosize zinc ferrite is believed to crystallize in a different way. It is now well established that in a nanosize zinc ferrite there is partial inversion in the cation occupancy, leading to some kind of magnetic ordering in this system much above its Neel temperature of 10 K. Hence, there is ample scope of maneuvering the electrical and magnetic properties of this ferrite. In the present study nanosize zinc ferrite was prepared by a chemical reaction involving the nitrates of Zn and Fe and using the citric acid as the host. The sintering of the precursor was done for 1 h at various temperatures ranging from 300°C to 1000°C. These samples were characterized by X-ray diffractometer (XRD), transmission electron microscopy (TEM), and electron paramagnetic resonance (EPR). The average particle sizes in these sintered samples measured by TEM are found to vary from ≈ 10 to 62 nm. The XRD measurements show the formation of single-phase spinel structure in all the samples. The X-band EPR spectrum of the precursor specimen at room temperature consists of two EPR signals: an intense signal at geff = 2.02 having peak-to-peak line width △HPP = 425 Gauss and other a weak signal at geff = 4.51 having an asymmetric line shape. As the samples are heat-treated at different temperatures, the EPR signal corresponding to the intense peak gets stabilized at geff ≈ 2.03, whereas the weak signal gets suppressed progressively. The spin–spin relaxation time in these samples have values ≈ 3 × 10-10s. The effect of sintering temperature on the properties of the nanostructured specimen of zinc ferrite and the underlying mechanism would be discussed.

Looking for the possibility of multiferroism in NiGd0.04Fe1.96O4 nanoparticle system

This paper reports the study of structural, electrical, magnetic and optical properties of Gd-doped nickel ferrite nanoparticles in order to investigate the possibility of multiferroism. The NiGd0.04Fe1.96O4 nanoparticles were prepared by a chemical route and characterized by various techniques. Doping with Gd ions induces poor ferroelectricity in nickel ferrite. This may be attributed to the small distortion in the centrosymmetric fcc structure because of the presence of large Gd ions.

QSAR modeling of synthesized 3-(1,3-benzothiazol-2-yl) 2-phenyl quinazolin-4(3H)-ones as potent antibacterial agents

Present communication elicits the designing and synthesis of 3-(1,3-benzothiazol-2-yl) 2-phenyl quinazolin-4(3H)-ones as potential antibacterial agents. A number of substituted 2-amino benzothiazoles, 2-amino-5-[(E)-phenyl diazenyl] benzoic acid, and 2-phenyl-4H benzo[d] [1,3] oxazin-4-one were synthesized as the precursor substrates. The compounds were synthesized in excellent yields and the structures were corroborated on the basis of IR, 1H NMR, Mass, and elemental analysis data. These compounds were screened in vitro for their antibacterial activity against a representative panel of Gram positive and Gram negative bacteria and models were generated through quantitative structure–activity relationship (QSAR).The activity contributions due to structural and substituent effects were determined using sequential regression procedure. The antimicrobial assay data show that the synthesized compounds are found to manifest profound antimicrobial activity.

Schottky-contacted vertically self-aligned ZnO nanorods for hydrogen gas nanosensor applications

Vertically well aligned ZnO nanorods (NRs) were grown on Si(100) substrate using RF magnetron sputtering technique. Scanning electron microscopy images confirms uniform distribution of NRs on 2 in. wafer with average diameter, height and density being ∼75 nm, ∼850 nm, and ∼1.5 × 1010 cm−2, respectively. X-ray diffraction reveals that the ZnO NRs are grown along c-axis direction with wurtzite crystal structure. Cathodoluminescence spectroscopy, which shows a single strong peak around 3.24 eV with full width half maxima 130 meV, indicates the high crystalline and optical quality of ZnO and very low defect density. Vertically aligned nanosensors were fabricated by depositing gold circular Schottky contacts on ZnO NRs. Resistance responses of nanosensors were observed in the range from 50 to 150 °C in 1% and 5% hydrogen in argon environment, which is below and above the explosive limit (4%) of hydrogen in air. The nanosensors sensitivity increases from 11% to 67% with temperature from 50 to 150 °C and also s...

In situ current-voltage characterization of swift heavy ion irradiated Au/n-GaAs Schottky diode at low temperature

A Au/n-GaAs(100) Schottky diode was irradiated at 80 r K by a 180 r MeV 107 Ag 14+ ion beam. In situ current-voltage (I--V) characterization of the diode was performed at various irradiation fluences ranging from 1 ‐ 10 10 to 1 ‐ 10 13 r ions r cm m 2 . The semiconductor was heavily doped (carrier concentration=1 ‐ 10 18 r cm m 3 ), hence thermionic field emission was assumed to be the dominant current transport mechanism in the diode. Systematic variations in various parameters of the Schottky diode like characteristic energy E 0 , ideality factor n , reverse saturation current I S , flatband barrier height K bf and reverse leakage current I R have been observed with respect to the irradiation fluence. The nuclear and electronic energy losses of the swift heavy ion affect the interface state density at the metal-semiconductor interface resulting in observed variations in Schottky diode parameters.

Pd/ZnO nanorods based sensor for highly selective detection of extremely low concentration hydrogen

We report highly hydrogen selective Pd contacted ZnO nanorods based sensor detecting low concentration even at low operating temperature of 50 °C. The sensor performance was investigated for various gases such as H2, CH4, H2S and CO2 at different operating temperatures from 50 °C to 175 °C for various gas concentrations ranging from 7 ppm to 10,000 ppm (1%). The sensor is highly efficient as it detects hydrogen even at low concentration of ~7 ppm and at operating temperature of 50 °C. The sensor’s minimum limit of detection and relative response at 175 °C were found 7 ppm with ~38.7% for H2, 110 ppm with ~6.08% for CH4, 500 ppm with ~10.06% for H2S and 1% with ~11.87% for CO2. Here, Pd exhibits dual characteristics as metal contact and excellent catalyst to hydrogen molecules. The activation energy was calculated for all the gases and found lowest ~3.658 kJ/mol for H2. Low activation energy accelerates desorption reactions and enhances the sensor’s performance.

Growth of residual stress-free ZnO films on SiO2/Si substrate at room temperature for MEMS devices

ZnO thick Stress relaxed films were deposited by reactive magnetron sputtering on 2”-wafer of SiO2/Si at room temperature. The residual stress of ZnO films was measured by measuring the curvature of wafer using laser scanning method and found in the range of 0.18 x 109 to 11.28 x 109 dyne/cm2 with compressive in nature. Sputter pressure changes the deposition rates, which strongly affects the residual stress and surface morphologies of ZnO films. The crystalline wurtzite structure of ZnO films were confirmed by X-ray diffraction and a shift in (0002) diffraction peak of ZnO towards lower 2θ angle was observed with increasing the compressive stress in the films. The band gap of ZnO films shows a red shift from ∼3.275 eV to ∼3.23 eV as compressive stress is increased, unlike the stress for III-nitride materials. A relationship between stress and band gap of ZnO was derived and proposed. The stress-free growth of piezoelectric films is very important for functional devices applications.

Covalency, hybridization and valence state effects in nano- and micro-sized ZnFe2O4

In the present work, Fe valence state, covalency effects, and metal–oxygen hybridization are discussed for ZnFe2O4 using X-ray absorption spectroscopy. A few sets of nano-sized and micro-sized zinc ferrite were synthesized using the nitrate method. Nanoparticles of ZnFe2O4 were synthesized by heating precursor at 300, 400, 500, 800, 1000, and 1200 °C for 1 h. To synthesize micro-sized ZnFe2O4, the obtained nanoparticles were annealed at 1200 °C for 12 h (bulk treatment). X-ray diffraction shows the presence of cubic spinel phase in nano-sized as well as micro-sized ZnFe2O4. Scanning electron microscopy measurements show that particle size ranges are 40–80 nm and 1–2 μm for nano-sized and micro-sized ZnFe2O4, respectively. Fe L-edge spectra of these materials envisage the presence of spectral features corresponding to t2g and eg symmetry states created due to Fe(2p3/2)-Fe(3d) and Fe(2p1/2)-Fe(3d) in octahedral crystal field. This reflects the presence of Fe3+ states in nano-sized and micro-sized ZnFe2O4. eg states dominate in micro-sized ZnFe2O4. O K-edge spectra for these materials can be distinguished by pre-edge and post-edge regions. Pre-edge and post-edge regions are associated with O(2p)–Fe(3d) and O(2p)–Fe(4s,4p) hybridized states. The extent of hybridization estimated from the intensity ratio of O(2p)–Fe(3d) and O(2p)–Fe(4s,4p) hybridized states is higher in nano-sized ZnFe2O4.

Electronic structure of Fe/MgO/Fe multilayer stack by X-ray magnetic circular dichroism

The interface properties of Fe/MgO/Fe multilayer stack were investigated by using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). The magnetic multilayers were deposited by electron beam evaporation method, which exhibits the attributes of perpendicular magnetic anisotropy (PMA). XAS analysis shows that Fe-layer forms a Fe-O-rich interface region with MgO-layer and a sum-rule analysis of the XMCD estimates the average magnetic moment of 2.31 ± 0.1 μB per Fe-atom. XAS and XMCD studies indicate the formation of a heterostructure (Fe/FeO/Fe2O3) on the interface. A phase transition in Fe-O stoichiometry at interface is also observed at low temperature (90 K), which may be useful in magnetic storage technology.

RELAXATION PHENOMENA IN NANOSTRUCTURED ZINC FERRITE

The electron paramagnetic resonance (EPR) is a well known tool to investigate the magnetic relaxation phenomena in the magnetic particles. For the present investigation, temperature variant EPR has been performed in order to study the relaxation mechanism in zinc ferrite nanoparticles. The magnetic nanoparticles were synthesized by using the nitrates of zinc and iron, and citric acid. The particle size of the samples were measured by the X-ray diffraction and Transmission Electron Microscopy. A more precise, Williamson–Hall (W–H) approach was used for the determination of the particle size as well as the strain in nanoparticles. The kinematics of magnetic moment has been studied with the help of temperature dependent EPR spectroscopy. Relaxation time calculations and temperature dependence of linewidth show the dominance of spin-lattice relaxation in these systems. Both nanoparticle systems show the presence of direct and Raman process in the relaxation mechanism and completely rule out the presence of Orbach process.