Non-equilibrium character of resistive switching and negative differential resistance in Ga-doped Cr2O3 system

We have synthesized Ga-doped Cr2O3 system with compositions Cr1.45Ga0.55O3 and Cr1.17Ga0.83O3 by chemical co-precipitation route and post annealing at 800^C. The samples have been stabilized in rhombohedral crystal structure with space group R3C. The present work focuses on the study of non-linear current-voltage (I-V) characteristics of the samples, which exhibited many interesting electronic properties, e.g., I-V loop, resistive switching, bi-stable electronic states, and negative differential resistance. The non-equilibrium character of the I-V characteristics has been studied by measurement of bias voltage cycling up to 20 times and current relaxation with time at set bias voltage. The charge conduction process in the samples has been understood by analysing I-V curves using different phenomenological models based on electrode-limited and bulk-limited charge conduction mechanisms proposed for metal electrode-metal oxide-metal electrode (M-MO-M) junctions. It is understood that competitions between injection of charge carriers from metal electrode to metal oxide, charge flow through the material (trapping/de-trapping and recombination of charge carriers at the defect sites), space charge formation at the junctions of electrodes and metal oxides, and ejection of electrons from metal oxide to metal electrode control the non-equilibrium I-V characteristics in the present samples.Comment: 24 pages, 10 figure

Shell model study of the pairing correlations

A systematic study of the pairing correlations as a function of temperature and angular momentum has been performed in the sd-shell region using the spherical shell model approach. The pairing correlations have been derived for even-even, even-odd and odd-odd systems near N=Z and also for the asymmetric case of N=Z+4. The results indicate that the pairing content and the behavior of pair correlations is similar in even-even and odd-mass nuclei. For odd-odd N=Z system, angular momentum I=0 state is an isospin, t=1 neutron-proton paired configuration. Further, these t=1 correlations are shown to be dramatically reduced for the asymmetric case of N=Z+4. The shell model results obtained are qualitatively explained within a simplified degenerate model

Observation of a γ\gamma-band based on two-quasiparticle configuration in 70^{70}Ge

The structure of $^{70}$Ge has been studied through in-beam gamma ray spectroscopy. A new band structure is identified that leads to forking of the ground-state band into two excited bands. Band structures have been investigated using the microscopic triaxial projected shell model approach. The observed forking is demonstrated to result from almost simultaneous band crossing of the two neutron aligned and the \gamma-band built on this two-quasiparticle configuration with the ground-state band.Comment: 9 pages, 13 figures, Accepted for publication as a Regular Article in PRC. in Physical Review C, 24th Feb 201

Onset of deformation at N=112N = 112 in Bi nuclei

The high spin states in $^{195}$Bi has been studied by $\gamma$-ray spectroscopic method using the $^{181}$Ta($^{20}$Ne, 6n) fusion evaporation reaction at 130 MeV. The $\gamma\gamma$ coincidence data were taken using an array of 8 clover HPGe detectors. The spin and parity assignments of the excited states have been made from the measured directional correlation from oriented states (DCO) ratios and integrated polarization asymmetry (IPDCO) ratios. The results show, for the first time, the evidence of a rotational like band based on a 13/2$^+$ band head in this nucleus, indicating the onset of deformation at neutron number $N = 112$ for the Bismuth isotopes. The results obtained were found to be consistent with the prediction of the total Routhian surface calculations using Woods Saxon potential. The same calculations also predict a change in shape from oblate to triaxial in $^{195}$Bi at high rotational frequency

Small Quadrupole Deformation for the Dipole Bands in 112In

High spin states in $^{112}$In were investigated using $^{100}$Mo($^{16}$O, p3n) reaction at 80 MeV. The excited level have been observed up to 5.6 MeV excitation energy and spin $\sim$ 20$\hbar$ with the level scheme showing three dipole bands. The polarization and lifetime measurements were carried out for the dipole bands. Tilted axis cranking model calculations were performed for different quasi-particle configurations of this doubly odd nucleus. Comparison of the calculations of the model with the B(M1) transition strengths of the positive and negative parity bands firmly established their configurations.Comment: 10 pages, 11 figures, 2 table

Re-entrant spin glass and magnetoresistance in Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide

We have investigated the static and dynamic response of magnetic clusters in Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide, where a sequence of magnetic phase transitions, i.e., paramagnetic (PM) to ferromagnetic at T_{C} $\leq$ 270K and ferromagnetic to canted spin glass state at T_f$$\leq$ 125K is observed

Finite to infinite steady state solutions, bifurcations of an integro-differential equation

We consider a bistable integral equation which governs the stationary solutions of a convolution model of solid--solid phase transitions on a circle. We study the bifurcations of the set of the stationary solutions as the diffusion coefficient is varied to examine the transition from an infinite number of steady states to three for the continuum limit of the semi--discretised system. We show how the symmetry of the problem is responsible for the generation and stabilisation of equilibria and comment on the puzzling connection between continuity and stability that exists in this problem

Low temperature ferromagnetic properties, magnetic field induced spin order and random spin freezing effect in Ni1.5Fe1.5O4 ferrite; prepared at different pH values and annealing temperatures

We present the low temperature magnetic properties in Ni1.5Fe1.5O4 ferrite as the function of pH at which the material was prepared by chemical route and post annealing temperature. The material is a ferri or ferromagnet, but showed magnetic blocking and random spin freezing process on lowering the measurement temperature down to 5 K. The sample prepared at pH =12 and annealed at 800 ^C showed a sharp magnetization peak at 105 K, the superparamagnetic blocking temperature of the particles. The magnetization peak remained incomplete within measurement temperature up to 350 K for rest of the samples, although peak temperature was brought down by increasing applied dc field. The fitting of temperature dependence of coercivity data according to Kneller law suggested random orientation of ferromagnetic particles. The fitting of saturation magnetization according to Bloch law provided the exponent that largely deviated from 1.5, a typical value for long ranged ferromagnet. An abrupt increase of saturation magnetization below 50 K suggested the active role of frozen surface spins in low temperature magnetic properties. AC susceptibility data elucidated the low temperature spin freezing dynamics and exhibited the characters of cluster spin glass in the samples depending on pH value and annealing temperature.Comment: 19 pages, 7 figure