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G. Rangarajan

Bio: G. Rangarajan is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Magnetic susceptibility & Magnetization. The author has an hindex of 14, co-authored 54 publications receiving 579 citations.


Papers
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Journal ArticleDOI
TL;DR: In this article, the conduction mechanism in PANI-PU blend is discussed in comparison to other commercial conducting polymer blends, and the percentage of Lorentzian and Gaussian spins are found to be delocalized.
Abstract: Charge transport in polyaniline protonated fully with methane sulphonic acid (MSA) and polyaniline (MSA)-polyurethane [PANI(MSA)-PU] blend has been investigated through measurements of temperature (T) and electric field (E) dependence of conductivity (\ensuremath{\sigma}), temperature dependence of thermoelectric power and magnetic susceptibility and electron spin resonance at room temperature. PANI(MSA) exhibits a three-dimensional variable-range hopping (VRH) type of conduction, which is not the case with HCl-doped PANI and the electric field dependence of its conductivity is also consistent with VRH behavior. The thermopower in PANI(MSA) shows metallic behavior. The blend follows a one-dimensional VRH type of conduction and the electric field dependence of its conductivity exhibits the Poole-Frenkel effect. The temperature-dependent magnetic susceptibility measurements indicate the presence of Pauli and Curie spins in both the samples. From electron spin resonance measurements the percentage of Lorentzian and Gaussian spins have been estimated. In PANI-MSA a larger number of spins are found to be delocalized. The conduction mechanism in PANI-PU blend is discussed in comparison to other commercial conducting polymer blends.

65 citations

Journal ArticleDOI
TL;DR: In this paper, the magnetocaloric effect in single crystalline nd−nd−0.7−Sr−Nd−1.3−nO−1−n−1 with respect to the Curie temperature was investigated.
Abstract: The magnetocaloric effect in single crystalline ${\mathrm{Nd}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ is investigated by measuring the field-induced adiabatic change in temperature $(\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}})$ which reveals a single negative peak around $130\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ well below the Curie temperature $({T}_{C}=203\phantom{\rule{0.3em}{0ex}}\mathrm{K})$. In order to understand this unusual magnetocaloric effect, we invoke the reported $^{55}\mathrm{Mn}$ spin-echo nuclear magnetic resonance, electron magnetic resonance and polarized Raman scattering measurements on ${\mathrm{Nd}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$. We show that this effect is a manifestation of a competition between the double exchange mechanism and correlations arising from coupled spin and lattice degrees of freedom which results in a complex ferromagnetic state. The critical behavior of ${\mathrm{Nd}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ near Curie temperature is investigated to study the influence of the coupled degrees of freedom. We find a complicated behavior at low fields in which the order of the transition could not be fixed and a second-order-like behavior at high fields.

56 citations

Journal ArticleDOI
TL;DR: In this paper, a tricritical point is observed in the Nd1−xSrxMnO3 (NSMO) (x=0.33) manganites at x = 0.33 which separates the first-order transition in NSMO-0.3 and second order transition of NSMO -0.4, and the contribution to the free energy from the presence of correlated clusters are strongly influencing the magnetocaloric effect.
Abstract: A tricritical point is observed in the Nd1−xSrxMnO3 (NSMO) (x=0.3, 0.33, and 0.4) manganites at x=0.33 which separates the first-order transition in NSMO-0.3 and second order transition in NSMO-0.4. The ferromagnetic transition of these compounds is further investigated by measuring magnetocaloric effect (MCE) and by applying a theoretical model based on Landau theory of phase transitions. Results indicate that the contributions to the free energy from the presence of correlated clusters are strongly influencing the MCE by coupling with the order parameter around the Curie temperature.

41 citations

Journal ArticleDOI
TL;DR: The paramagnetic electron-spin resonance (ESR) linewidth of polycrystalline Nd1−xSrxMnO3 (x=0.3, 0.4, and 0.5) increases in a quasilinear manner up to 400 K due to the formation of paramagnetic clusters, which is also confirmed by the activation behavior of the ESR intensity above TC as mentioned in this paper.
Abstract: The paramagnetic electron-spin resonance (ESR) linewidth of polycrystalline Nd1−xSrxMnO3 (x=0.3, 0.33, 0.4, and 0.5) increases in a quasilinear manner up to 400 K due to the formation of paramagnetic clusters, which is also confirmed by the observation of an activated behavior of the ESR intensity above TC. Upon cooling, a pair of ferromagnetic resonance lines appear well above the magnetic transition temperature (TC, TN) in all cases. This suggests the presence of ferromagnetic clusters at a temperature T*>TC. The two-line structure below T* is discussed in terms of phase separation and formation of magnetic clusters and their coexistence with a charge-ordered phase for x>0.4.

40 citations

Journal ArticleDOI
TL;DR: In this article, a conductive polymer is found in the IM transition without applying pressure, and the transition to the metallic state is associated with a decrease of the C6-N-C6 angle from 166° to 134°.
Abstract: Melt dispersion processing--without solvents or “secondary dopants”--pushes polyaniline reproducibly to the metallic side of the IM transition, although the undispersed polyaniline is on the insulator side. This is the first time that a conductive polymer is found there without applying pressure. The transition to the metallic state is associated with a decrease of the C6-N-C6 angle from 166° to 134°.

33 citations


Cited by
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01 Sep 1955
TL;DR: In this paper, the authors restrict their attention to the ferrites and a few other closely related materials, which are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present.
Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

2,659 citations

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TL;DR: A review of the properties of pyrochlore oxides can be found in this paper, mainly from a materials perspective, but with an appropriate theoretical context, where the authors attempt to review the myriad of properties found in the oxides.
Abstract: Within the past 20 years or so, there has occurred an explosion of interest in the magnetic behavior of pyrochlore oxides of the type $A_{2}^{3+}$$B_{2}^{4+}$O$_{7}$ where $A$ is a rare-earth ion and $B$ is usually a transition metal. Both the $A$ and $B$ sites form a network of corner-sharing tetrahedra which is the quintessential framework for a geometrically frustrated magnet. In these systems the natural tendency to form long range ordered ground states in accord with the Third Law is frustrated, resulting in some novel short range ordered alternatives such as spin glasses, spin ices and spin liquids and much new physics. This article attempts to review the myriad of properties found in pyrochlore oxides, mainly from a materials perspective, but with an appropriate theoretical context.

962 citations

Journal ArticleDOI
TL;DR: In this paper, various preparation methods, physical properties, and potential applications of one-dimensional nanostructures of conjugated polyaniline (PANI), polypyrrole (PPY) and poly(3,4-ethylenedioxythiophene) (PEDOT) are summarized and reviewed.

740 citations

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TL;DR: In this paper, the authors compared electronic transport properties of conjugated organic conducting polymers, polysulphur nitride, alkali-metal fulleride polymers and carbon nanotubes.
Abstract: We review and compare electronic transport in different types of conducting polymer: conjugated organic polymers, the inorganic polymer polysulphur nitride, alkali-metal fulleride polymers, and carbon nanotubes. In each case, the transport properties show some unusual features compared to conventional metals. In conjugated organic conducting polymers, electronic transport shows a systematic pattern involving both metallic and non-metallic character. We discuss the physical conduction processes that can account for this behaviour. Key roles are played by the metal-semiconductor transition as the doping level is varied, and by the limited size of crystalline regions in the polymers, which gives rise to heterogeneous conduction. Transport data provide indirect evidence that the intrinsic conductivity of doped crystalline polyacetylene, in the absence of disordered regions, is higher than that of copper at room temperature; this high conductivity is consistent with the expected suppression of backscattering in highly anisotropic ('quasi-one-dimensional') metallic conduction. Bundles of single-wall carbon nanotubes have also been found to exhibit metallic behaviour. The temperature dependence of the conductivity of bulk samples is remarkably similar to the pattern characteristic of organic conducting polymers, typically showing a crossover from metallic to non-metallic behaviour as temperature decreases. Quantized one-dimensional conductance and other quantum effects are seen in individual nanotubes.

390 citations

Journal ArticleDOI
TL;DR: The properties of the Y1−xPrxBa2Cu3O7 (YPrBCO) system are reviewed in this paper, including superconducting, normal state, structural, chemical, optical, magnetic, and thermal properties.
Abstract: The properties of the Y1−xPrxBa2Cu3O7 (YPrBCO) system are reviewed. These include superconducting, normal state, structural, chemical, optical, magnetic, and thermal properties. The destruction of superconductivity with Pr doping is discussed in view of possible models such as hole filling, localization, magnetic pair-breaking, and the role of hybridization. Applications to electronic devices using YBCO/PrBCO/YBCO multilayers are also reviewed.

327 citations