Existence of Nearest Neighbor and Variable Range Hopping in Pr2_2ZnMnO6_6

A joint investigation of X-ray diffraction (XRD) pattern and Raman spectrum authenticate the double phase monoclinic P21/n and cubic Fd-3m structures of polycrystalline Pr2ZnMnO6 (PZM). The existence of two different conduction mechanisms (Nearest neighbor hopping and Motts variable range hopping) is observed using a combined study of conductivity, dielectric relaxation and impedance spectra in PZM. This investigation point towards a transition from nearest neighbor hoping to Motts variable range hopping mechanism due to lowering activation energy around 580 K. The charge carriers hopping between the localized acceptor states at the grain boundaries (GBs), which dominants conduction mechanism below 580 K. The ac conductivity, dielectric relaxation, Nyquist plot, and electric modulus highlight the blended effect of grains (Gs) and GBs leads to the charge carrier dynamics in PZM. The dielectric relaxation and modulus formalism are analyzed on the basis of empirical Cole-Cole model. The conduction mechanism is found to be highly correlated with the relaxation mechanism and impedance spectroscopy.Comment: 15 page

Characterizations of GEM detector prototype

At NISER-IoP detector laboratory an initiative is taken to build and test Gas Electron Multiplier (GEM) detectors for ALICE experiment. The optimisation of the gas flow rate and the long-term stability test of the GEM detector are performed. The method and test results are presented.Comment: 3 Pages, 4 figure

Crossover between small polaron hopping and Mott's variable range hopping in Pr2MgTiO6

A combined study of X-ray diffraction (XRD) pattern and Raman spectrum authenticates the lower symmetric orthorhombic Pnma structure for solid-state synthesized Pr2MgTiO6 (PMT). The Ag mode demonstrates itself as a breathing vibration of the TiO6 octahedra. The ac conductivity, dielectric relaxation, and impedance spectra highlight the joint contributions of the grain-boundaries and grain microstructures to the charge carrier dynamics in PMT. The double power-law formalism is accepted to fit ac conductivity spectra. The relaxation spectra has a non-ideal nature with the circulation of relaxation time as observed from the impedance spectroscopic data. An equivalent circuit model has been employed for fitting impedance data using a constant phase element (CPE) model. The dc conductivity investigation points towards a crossover from small polaron hopping to Mott s variable range hopping due to lowering activation energy. The crossover between two different conduction mechanisms (Mott s variable range and small polaron hopping) is investigated using a conjunction of thermal varying conductivity, dielectric relaxation and impedance spectrum in polycrystalline PMT.Comment: 10 pages, 5 figures, 4 tables. arXiv admin note: substantial text overlap with arXiv:1707.02830, text overlap with arXiv:1904.1196

Combining ability studies in restorer lines of sunflower (Helianthus annuus L.)

The restorer lines are used to get fertile hybrids in hybrid seed production system of sunflower. Improve-ment of R-lines for fertility and oil content of sunflower is required to get desirable hybrids upon crossing. In the pre-sent study, 6 restorer lines were crossed in full diallele and both direct and reciprocal crosses along with parents were evaluated for their combining ability. The analysis of variance revealed higher magnitude of SCA variance than GCA variance for all the characters studied except for days to 50 per cent flowering. Among six parents, GMU -520 and R-GM-41 were best general combiner for plant height, head diameter, test weight and leaf size in the desired direction. However, GMU-520 has advantage of yield per plant and oil content. From 15 direct crosses R-GM-41 x R -GM-49 exhibited significant specific combining ability for viz., days to 50 per cent flowering (-1.08), plant height (13.69), head diameter (4.79), leaf size (0.74), yield per plant (17.14), volume weight (2.54), test weight (1.75) and oil content (0.34) followed by RCR-630 x GMU-520, R-GM-41 x EC-602060, R-GM-49 x GMU-520 and EC-602060 x GMU-520 each exhibiting good specific combining ability for majority of characters. Among reciprocal crosses R-GM -41 x RCR-8 exhibited a high reciprocal effects for head diameter (4.57), yield per plant (15.16), test weight (2.02) and leaf size (0.75)

Structural relaxation of E' gamma centers in amorphous silica

We report experimental evidence of the existence of two variants of the E' gamma centers induced in silica by gamma rays at room temperature. The two variants are distinguishable by the fine features of their line shapes in paramagnetic resonance spectra. These features suggest that the two E' gamma differ for their topology. We find a thermally induced interconversion between the centers with an activation energy of about 34 meV. Hints are also found for the existence of a structural configuration of minimum energy and of a metastable state.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let

Properties of low-lying states in some high-nuclearity Mn, Fe and V clusters: Exact studies of Heisenberg models

Using an efficient numerical scheme that exploits spatial symmetries and spin parity, we have obtained the exact low-lying eigenstates of exchange Hamiltonians for the high nuclearity spin clusters, Mn_{12}, Fe_8 and V_{15}. The largest calculation involves the Mn_{12} cluster which spans a Fock space of a hundred million. Our results show that the earlier estimates of the exchange constants need to be revised for the Mn_{12} cluster to explain the level ordering of low-lying eigenstates. In the case of the Fe_8 cluster, correct level ordering can be obtained which is consistent with the exchange constants for the already known clusters with butterfly structure. In the V_{15} cluster, we obtain an effective Hamiltonian that reproduces exactly, the eight low-lying eigenvalues of the full Hamiltonian.Comment: Revtex, 12 pages, 16 eps figures; this is the final published versio

Evaluation of low-energy effective Hamiltonian techniques for coupled spin triangles

Motivated by recent work on Heisenberg antiferromagnetic spin systems on various lattices made up of triangles, we examine the low-energy properties of a chain of antiferromagnetically coupled triangles of half-odd-integer spins. We derive the low-energy effective Hamiltonian to second order in the ratio of the coupling J_2 between triangles to the coupling J_1 within each triangle. The effective Hamiltonian contains four states for each triangle which are given by the products of spin-1/2 states with the states of a pseudospin-1/2. We compare the results obtained by exact diagonalization of the effective Hamiltonian with those obtained for the full Hamiltonian using exact diagonalization and the density-matrix renormalization group method. It is found that the effective Hamiltonian is accurate only for the ground state for rather low values of the ratio J_2 / J_1 and that too for the spin-1/2 case with linear topology. The chain of spin-1/2 triangles shows interesting properties like spontaneous dimerization and several singlet and triplet excited states lying close to the ground state.Comment: Revtex, 11 pages, 11 eps figure