A scaling formalism is used to analyze non-Ohmic conductance-voltage data in nanowires of an isolated potassium manganese oxide K0.27MnO2·0.5H2O and a poly(3,4-ethylenedioxythiophene) (PEDOT) and nanotubes of conducting polypyrrole at different temperatures. This scaling analysis provides a single voltage scale for non-Ohmic conduction which scales with Ohmic conductance with an exponent xT, called nonlinearity exponent. A detailed analysis reveals that the onset exponents xT are different in different systems. Non-Ohmic conduction and the nonlinearity exponents in these low-dimensional nanostructures are analyzed within the framework of scaling approach and existing theoretical models. © 2013 The Authors.

U N NANDI

D CHAKRABORTY

Fulltext

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Results in Physics

The dielectric permittivity of yttrium-doped polycrystalline samples La1−x−yYyCaxMnO3 with x=0.05,0.33 and y=0.07 has been measured at frequencies f from 20 Hz to 2 MHz and at temperatures T from 80K to 350K. These samples were prepared in the form of bulk polycrystals(ceramics) by solid state reaction method and characterized by X-ray diffraction technique. With the decrease in temperature, this system exhibits a phase transition from paramagnetic insulating to ferromagnetic metallic at a temperature TMI=225K for x=0.05 and at 170K for x=0.33. In this report, it is shown that such phase transition can be characterized by the exponents obtained from the scaling analysis of the variation of the real and the imaginary part of the dielectric permittivity ϵ1 and ϵ2 and the loss factor tanδ as a function of frequency and temperature. Results are analyzed systematically from the existing theoretical models and the scaling formalism. © 2016

Physica B: Condensed Matter

Characterization of magnetic phase in yttrium-doped polycrystalline La1âˆ’xâˆ’yYyCaxMnO3 with x=0.05,0.33 and y=0.07 using dielectric and optical parameters

The signature of various disordered phases is inferred from the measurement of the real part of alternating current conductance Σ(T, f) of a nanocrystalline double perovskite La2NiMnO6. The system exhibits a paramagnetic insulating (PMI) phase at high temperatures, a ferromagnetic insulating (FMI) phase at low temperatures, and a Griffiths-like phase in the intermediate temperature range. In these three phases, Σ(T, f) shows qualitatively similar variation with frequency f. At a fixed temperature T, Σ(T, f) remains constant to its Ohmic value Σ0 up to a certain frequency, known as the onset frequency fc and increases with increasing f beyond fc. Scaled appropriately, Σ(T, f) versus f data corresponding to these three regimes fall on the same master curve indicating the universal nature of the scaling behaviour of alternating current conductance. This onset frequency fc scales with Σ0 as f c ∼ Σ 0 x f with xf as the nonlinearity exponent. This exponent xf shows a gradual crossover from 1.025 ± 0.006 in FMI phase to 0.518 ± 0.07 in PMI phase in an intermediate temperature range signifying the presence of Griffiths-like phase. A simple phenomenological R-RC model consistent with the microstructural conduction mechanisms in PMI and FMI phases is developed to generate the qualitative non-Ohmic character of ac conductance, the onset frequency fc, and the nonlinearity exponent xf. Existing scaling theories with reliable models are used to analyze and compare the results of ac conductance in similar systems. © 2015 AIP Publishing LLC.

Journal of Applied Physics

Magnetic phase characterization of nanocrystalline La2NiMnO6 using alternating current conductance

The real part of ac conductance Σ(T, f) of yttrium-doped mixed-valent polycrystalline manganite systems La1 x yYyCaxMnO3 with x = 0.33 and 0.05 and y = 0.07 and iron doped LaMn1 xFexO3 with x = 0.15 is measured as a function of frequency f by varying zero-frequency Ohmic conductance Σ0 by T. The former shows a metal-insulator transition, whereas the latter exhibits insulating character throughout the measured temperature range. At a fixed temperature T, Σ(T, f) remains almost constant to the value Σ0 up to a certain frequency, known as the onset frequency fc and increases from Σ0 as frequency is increased from fc. Scaled appropriately, the data for Σ(T, f) at different T fall on the same universal curve, indicating the existence of a general scaling formalism for the ac conductance. fc scales with Σ0 as fc∼Σ0xf, where xf is the nonlinearity exponent characterising the onset. With the help of data for ac conduction, it is shown that xf is very much phase sensitive and can be used to characterize the different phases in a manganite system originated due to change in temperature or disorder. Scaling theories and existing theoretical models are used to analyze the results of ac conduction and the nonlinearity exponent xf. © 2014 AIP Publishing LLC.

Journal	Data powered by TypesetResults in Physics
Publisher	Data powered by TypesetELSEVIER SCIENCE BV
ISSN	2211-3797
Open Access	Yes