Aparna Nath - Academia.edu (original) (raw)

Papers by Aparna Nath

Advanced Materials Proceedings, 2017

Journal of Physics: Conference Series, 2019

Indian Journal of Physics, 2020

Formations of complex structures observed during the instability instigated expanding capacitive ... more Formations of complex structures observed during the instability instigated expanding capacitive mode of RF discharge in a linear vacuum vessel, in the absence of an externally applied magnetic field or any other additional constraint applied. Systematic measurements of the plasma parameters, using multiple probe diagnostics, carried out to investigate the parametric dependence of sheath development reveal visible cylindrical tube like multiple double-layer formations around a mesh-type cylindrical plasma source. Such firetube formations provide many interesting and vital information on expanding radio frequency (RF) plasma sheath, charge particle trapping and the associated sheath instability with the RF discharge. The sheath structures, glowing spot formations, space charge formations, complex structure and firetube formations in the expanding plasma are some of the features discussed here in relation to such an expanding RF discharge. Low-frequency sheath instabilities are also observed in connection to the firetube formations using a coaxial mesh-type cylindrical plasma source powered at an operating frequency of 13.56 MHz. The ion acoustic frequency-dominated instability is identified as a sheath-plasma instability associated with the RF plasma.

Journal of Molecular Liquids, 2020

Temperature dependent optical properties like birefringence, temperature gradients of refractive ... more Temperature dependent optical properties like birefringence, temperature gradients of refractive indices, molecular polarizabilities, effective geometry parameter, order parameter and cross over temperatures have been investigated for nine different liquid crystal mixtures. These mixtures are prepared by mixing two pure nematic liquid crystal compounds, namely, 4-n-pentyl phenyl 4-n′-hexyloxybenzoate (ME6O.5) and 4-cyanophenyl 4′n-pentyl benzoate (CPPB) where, ME6O.5 is a monotropic compound and CPPB is an enantiotropic compound. The mixtures however are found to be exhibit induced smectic phases. The theoretical fitting values obtained by using Hallers' extrapolated method of birefringence values agree quite well with the experimental values. It is observed that the normalized polarizability behaves exactly as refractive indices when it is plotted against temperature. The effective geometry parameter (α eg) of the mixture having highest birefringence shows highest value of α eg at certain temperature. Finally, order parameters of the mixtures have been calculated using five different techniques and for all mixtures the order parameters shows characteristics range from 0.3-0.9. The abrupt changes in order parameter before nematic phases are due to the existence of the induced smectic phases in the liquid crystal mixtures.

The European Physical Journal B, 2019

Abstract We report electrical and magneto-transport properties of La0.7Sr0.3MnO3(LSMO)/Paraffin w... more Abstract We report electrical and magneto-transport properties of La0.7Sr0.3MnO3(LSMO)/Paraffin wax nanocomposites prepared through low temperature chemical pyrophoric reaction process. A core shell structure is expected to be formed having a ferromagnetic LSMO core and a spin disordered shell of paraffin wax. Enhanced charging energy due to coulomb blockade contribution with increasing paraffin wax is observed for the composites attributing enhanced intergranular distance between LSMO grains. Effective spin-polarized tunneling of conduction electrons resulting in sharp low field magnetoresistance (MR) of the composites is due to reordering of spin disorder at paraffin wax shell with magnetic field. Moreover, observation of enhanced magnetoresistive hysteresis with decrease in temperature has been attributed to increased blocked states at LSMO grain surface. Calculated surface spin susceptibility (χb) has been found to follow similar behavior of MR with temperature indicating surface magnetization dependent MR. Fitting of magnetoconductance versus field curves reveal increase of Para to ferro transition temperature, TC and χb indicate higher antiferromagnetic coupling of shell spins for composite samples than pristine LSMO above 50 K. χb also indicate systematic decrease in surface spin disorder of the composite samples with respect to pure LSMO which is expected to be due to the probable covalent bond formation between Paraffin wax molecules and surface atoms of LSMO nanoparticles. Graphical abstract

Journal of Alloys and Compounds, 2019

Magnetoelectric coupling, magnetoimpedance and dielectric properties are investigated for spincha... more Magnetoelectric coupling, magnetoimpedance and dielectric properties are investigated for spincharge dependent magnetoelectric LaFeO 3-poly(vinylidene fluoride) hybrid nanocomposites. The X-ray diffraction pattern indicates that both LaFeO 3 and poly(vinylidene fluoride) phases coexist in the nanocomposites. The magnetoelectric coupling measurement confirms the multiferroic in nature of the nanocomposites. Magnetoelectric and magnetocapacitance (~ 42%) effects are ascribing the improvement of space charge polarization of nanocomposites. The light of classical electrodynamics causes the room temperature magnetoimpedance effect (~ 94%). Temperature dependent ac conductivity suggests the observation of negative temperature coefficient resistance behavior that also obeys the single Jonscher's power law. The conduction mechanism of the system is controlled through small and large polaronic hopping. Activation energy of those polymer based hybrid nanocomposites is estimated using Arrhenius relation. The magnetoelectric coupling of the nanocomposites is enhanced with an increase in poly(vinylidene fluoride) content. The inorganic-organic based nanocomposites could be a favorable candidate for improvement of magnetoelectric devices, smart energy storage and energy harvesting device applications.

Optical Materials, 2018

The temperature dependent properties of three liquid crystals (LC) namely effective geometry para... more The temperature dependent properties of three liquid crystals (LC) namely effective geometry parameter, order parameter and temperature gradients of refractive indices of two fluorinated isothiocyanato nematic liquid crystal (NLC) compounds 4′-pentylcyclohexyl-3,5-difluoro-4-isothiocyanatobiphenyl, 4'−butylcyclohexyl−3, 5− difluoro− 4− isothiocyanato-biphenyl of high clearing temperature (T C) and low T C LC compound 4 (trans-4 /-n-hexycyclohexyl) isothiocyanatobenzene (6CHBT) have been studied. In this paper, the effective geometry parameters of the three LC compounds are calculated. The order parameters of three LC compounds are also calculated from the effective geometry parameter. From the available data, it is found that the two fluorinated NLC compounds exhibit moderately high value of birefringence (∼0.24-0.26) and 6CHBT exhibits a lower value of birefringence (∼0.16). From the study, it is found that the order parameter is found to be higher in higher birefringence and higher T C LC compounds. The values of temperature gradient of ordinary refractive index (dn o /dT) are found to be showing negative to positive value while increasing temperature which gives the crossover temperature (T CO). The crossover temperature has been calculated from the temperature gradient at the value (dn o /dT) = 0. LC compounds with lower T C are found to have larger T CO value which gives narrower temperature between T CO and T C. The T CO value of compound having larger alkyl group is found to be smaller. The Lorentz field factors for both compound are also reported which can be used for order parameter calculation by different aspects.

International Journal of Modern Physics B, 2018

We have investigated strain mediated magnetoelectric (ME) coupling and impedance properties in 0.... more We have investigated strain mediated magnetoelectric (ME) coupling and impedance properties in 0.5Zn[Formula: see text]Ni[Formula: see text]Fe2O4–0.5HoMnO3 nanocomposites at room-temperature. The ME voltage is measured in both longitudinal and transverse direction at a frequency of 173 Hz. The impedance, real and imaginary parts of impedance and dielectric constant have been carried out in presence of DC magnetic field. With the application of magnetic field, slight decrease in dielectric constant has been observed. The impedance, real and imaginary parts of impedance are found to increase with the increase in the applied magnetic field. Nyquist plots have been fitted using three parallel combinations of resistances–capacitance circuits. Fitted parameters show the dominant role of grain boundaries, grains and interface of two types of grains of the sample.

DAE SOLID STATE PHYSICS SYMPOSIUM 2018, 2019

Dysprosium-substitution induced effects on the structural, dielectric and magnetic properties of ... more Dysprosium-substitution induced effects on the structural, dielectric and magnetic properties of CoFe 2 O 4

DAE SOLID STATE PHYSICS SYMPOSIUM 2018, 2019

We have investigated complex impedance spectroscopy and magnetoresistance(MR) of 99.5% La 0.7 Sr ... more We have investigated complex impedance spectroscopy and magnetoresistance(MR) of 99.5% La 0.7 Sr 0.3 MnO 3 (LSMO)-0.5% Glass nanocomposite material. We suppose, thin Glass boundary is formed at LSMO surface where depinning of grain boundary(GB) domain walls take place, from GB pinning centres, on application of magnetic field(H). Moreover, on application of temperature, conducting electrons at glass interface gain more thermal energy which also lead to temperature dependent electrical relaxation of the system. However the composite become more insulating on glass addition due to presence of intergranular glass barrier between neiboring LSMO grains. But surprisingly, MR of the composite indicate formation of very efficient spin polarized tunnel barrier on addition of glass at room temperature.

Journal of Molecular Liquids, 2019

In this study, we have chosen a room temperature nematic liquid crystal (NLC) compound namely, 6C... more In this study, we have chosen a room temperature nematic liquid crystal (NLC) compound namely, 6CHBT [trans-4'-n-hexylcyclohexyl) isothiocyanatobenzene] having clearing temperature at 42.8°C. This particular liquid crystal (LC) exhibits a broad nematic phase from 13°C to 42.8°C. Among all the available spectroscopy techniques, Raman spectroscopy is one of the most convenient technique to understand the various phase transitions of a LC compound. In order to understand the phase change and the change of the molecular orientations along with their change in the chemical bond, the temperature dependent Raman study has been conducted for the LC compound 6CHBT. The transition temperatures of various phases obtained from the linewidth peak positions of Raman spectra agrees well with the literature data. From the Raman spectra, the change in chemical bonds are observed which is due to the increase in the molecular orientation of the alkyl chain in the LC compound. The bond assignment of the experimental value agrees well with the Raman assignment obtained from literature. 1. Introduction: Liquid crystals (LCs) are known for their incredible behaviour and found intermediate between a solid crystalline state and an isotropic liquid state. LCs are anisotropic in nature and have anisotropic optical, electrical and magnetic properties. Because of this anisotropic property, they find a wide applicability in electro-optic devices. The molecules in the LCs are oriented in a particular direction of the LC plane, known as the director. Due to its tremendous orientational properties with respect to the director, LCs are widely used in display devices. Some of the LCs show the first order and second order non-linear optical properties and for these properties, it is industrially used in non-linear optical devices [1-7].

Materials Chemistry and Physics, 2019

Nanocomposites of xNiFe 2 O 4-(1-x)ZnO (x = 0.2, 0.3 and 0.5) have been prepared through chemical... more Nanocomposites of xNiFe 2 O 4-(1-x)ZnO (x = 0.2, 0.3 and 0.5) have been prepared through chemical "pyrophoric reaction process". Structural characterizations confirm the formation of both NiFe 2 O 4 and ZnO phases in nanocomposites. The room temperature magnetoelectric coupling, dielectric and temperature dependence of electrical properties of the prepared nanocomposites have been investigated. The observed magnetoelectric coupling may be owed to the field dependent magnetostriction property of the piezomagnetic phase of the nanocomposites. The magnetoelectric voltage is measured in both transverse and longitudinal directions. Electrical transport studies are carried out using an ac impedance spectroscopy and dc resistivity techniques. Metal-semiconductor transition of the nanocomposites has been explained on the light of delocalized and localized charge carrier. Detailed analysis of ac conductivity with frequency at varying temperature suggests the thermally activated electronic transport conduction mechanism for large and small polaronic hopping in the nanocomposites. The semiconducting band gap of the nanocomposites has also been estimated using recorded absorbance spectra. Light-dependent current-voltage characteristics are non-Ohmic in nature and exhibit significant electrical memory effect with resistive switching. On light illumination, there is a significant decrement in current with quenching of hysteresis loop suggesting high recombination of the photo-generated carriers.

Journal of Magnetism and Magnetic Materials, 2019

Room temperature magnetoimpedance and magnetodielectric effects for (100 − x)% LaFeO 3 − x% organ... more Room temperature magnetoimpedance and magnetodielectric effects for (100 − x)% LaFeO 3 − x% organic paraffin wax (x = 0, 0.5, 1, 1.5%) hybrid nanocomposites have been investigated. The enhancement of magnetoimpedance (∼226%) and magnetodielectric (∼75%) effects at low frequency region are obtained for x = 0.5% nanocomposites for strain mediation of piezomagnetic materials. The observed currentvoltage characteristics both in absence and presence of magnetic field at room temperature have corroborated with the enhanced effect. It is also showing electrical memory effect with electrical switching. The Nyquist plots have been fitted considering the parallel combination of resistance-constant phase element circuit. AC electrical studies reveal the conduction mechanism in the system controlling through the grain and grain boundaries of nanocomposites. The minimum grain and grain boundaries resistance are found for x = 0.5% nanocomposites. The electric modulus of these nanocomposites has been studied to separate the grain and grain boundaries contributions of the system. A phenomenological model has been demonstrated to explain the observed result considering the barrier width of paraffin wax layer across the grain boundaries of LaFeO 3 nanoparticles. The observed transport behavior attributes the phenomenological model. The organic hybrid nanocomposites (x = 0.5%) may be worked as a resistance-capacitance-inductance circuit with voltage magnification.

Journal of Materials Science: Materials in Electronics, 2019

Effect of particles size on the behavior of magnetoimpedance, magnetodielectric and detailed elec... more Effect of particles size on the behavior of magnetoimpedance, magnetodielectric and detailed electrical properties of structural characterized LaFeO 3 nanoparticles prepared through chemical 'pyrophoric reaction' technique having particles size of ~ 21, 43 and 51 nm have investigated. Dielectric constant of these nanoparticles gives the evidence of space charge polarization in the sample at lower frequency regime. Maximum magnetodielectric effect is obtained to ~ 61% at room temperature for particle size of ~ 21 nm, which may be due to the large surface to volume ratio of this nanoparticles compared to other particles size attributing the enhancement of space charge polarization. The maximum value of magnetoimpedance is found to ~ 92% for ~ 21 nm nanoparticle at room temperature. Magnetic field and frequency dependence room temperature magnetoimpedance are decreased with particles size of the nanoparticles. This behaviour has been explained through the light of classical electrodynamics, which reveals that this effect is depending on the magnetic field and ac signal frequency. Impedance spectroscopy is employed to study the electrical transport properties of the samples considering an equivalent circuit model for the effect of nanometric grain size. The electrical relaxation process of these materials is temperature dependent. Furthermore, ac conductivity curves follow the Jonscher's power law for electrical conduction process of the system through polaronic hopping.

Physics of Plasmas, 2018

Intensely luminous double layers develop and then expand in size in a visibly glowing RF discharg... more Intensely luminous double layers develop and then expand in size in a visibly glowing RF discharge produced using a plasma source consisting of a semi-transparent cylindrical mesh with a central electrode, in a linear plasma chamber. Although RF discharge is known to be independent of device geometry in the absence of magnetic field, the initiation of RF discharge using such a plasma source results in electron drift and further expansion of the plasma in the vessel. The dynamics of complex plasma structures are studied through electric probe diagnostics in the expanding RF plasma. The measurements made to study the parametric dependence of evolution of double layer structures are analyzed and presented here. The plasma parameter measurements suggest that the complex potential structures initially form with low potential difference between the layers and then gradually expand producing burst oscillations. The present study provides interesting information about the stability of plasma sheath and charge particle dynamics in it that are important to understand the underlying basic sheath physics along with applications in plasma acceleration and propulsion.

Materials Letters, 2018

Room temperature magnetoelectric coupling, magnetic field dependent dielectric and ac electrical ... more Room temperature magnetoelectric coupling, magnetic field dependent dielectric and ac electrical properties of xLa 0.7 Sr 0.3 MnO 3-(1 À x) Poly(vinylidene fluoride) (x = 0.5, 0.6 and 0.7) nanocomposites have been investigated. The magnetoelectric voltage coefficients are found to 0.25and0.25 and 0.25and0.16 mV/cmOe for transverse and longitudinal configurations. Dielectric constants for all the compositions are increased with increase in magnetic field. Magnetodielectric value is estimated to $16% due to the magnetostriction property of the samples. The fitted value of Nyquist plots reveals the dominant role of the grain boundaries of La 0.7 Sr 0.3 MnO 3 nanoparticles and modified grain boundaries due to Poly(vinylidene fluoride) in the samples. With the application of magnetic field the relaxation frequencies are shifted towards the higher frequency region attributing to the magnetic field dependent relaxation process in the system.

Journal of Alloys and Compounds, 2017

Magnetoelectric coupling, dielectric and electrical properties of xLa 0.7 Sr 0.3 MnO 3-(1−x) Pb (... more Magnetoelectric coupling, dielectric and electrical properties of xLa 0.7 Sr 0.3 MnO 3-(1−x) Pb (Zr 0.58 Ti 0.42)O 3 (x = 0.05 and 0.1) multiferroic nanocomposites

Journal of Molecular Liquids, 2016

Study of optical texture of different mesophases and phase transition temperatures of the liquid ... more Study of optical texture of different mesophases and phase transition temperatures of the liquid crystal compound 4,4′-din -heptyloxy-azoxy benzene has been carried out by using optical polarizing microscope. Enthalpy values and the phase transition temperatures have also been conducted by DSC studies. The variation of refractive indices with temperature has been measured by a thin prism technique using He-Ne laser and temperature dependent birefringence is calculated which shows a moderate value. Validation of the modified four-parameter model based on Vuks approximation has been carried out and reported in this article. The most important characteristics of LC compound namely macroscopic and microscopic order parameter have been evaluated by using direct extrapolation method and modified Vuks method based on Haller's extrapolation respectively. Temperature gradients of refractive indices have also been calculated. Further the normalized polarizabilities for extraordinary and ordinary rays and their ratio have been reported in this paper.

Journal of Applied Physics, 2015

Detailed magnetically tunable ac electrical properties of x La 0.7 Sr 0.3 MnO 3 (LSMO)-(1 À x) Er... more Detailed magnetically tunable ac electrical properties of x La 0.7 Sr 0.3 MnO 3 (LSMO)-(1 À x) ErMnO 3 (EMO) (x ¼ 0.1, 0.3, and 0.5) multiferroic nanocomposites have been studied at 300 K in presence of varying magnetic field (H appl), applied both in parallel and perpendicular configuration with respect to the measuring electric field. AC electrical properties have exhibited significant variation with H appl for all composites, whereas for parallel configuration of H appl such effect is very feeble for x ¼ 0.3 composite. We have attributed this anisotropic behavior to the demagnetization effect in the sample. In contrast, for x ¼ 0.1 and 0.5 composites, no such anisotropy effect is experimentally evidenced. Impedance and real part of impedance have been found to decrease with H appl at low frequency (f) region. We attribute this observation to the depinning of the magnetic domain walls from the grain boundaries pinning centers and thereby enhancing the spin dependent transport in the composite. For x ¼ 0.3 composite, Nyquist plots have been fitted considering dominant contributions of LSMO and EMO grain boundaries and the interface region between them. However, for x ¼ 0.1 composite, it corresponds to EMO grain boundaries and grain boundary interface region. The relaxation frequency (f R) is observed to shift at higher/lower f region in perpendicular/parallel configuration of H appl for x ¼ 0.3 composite. This opposite variation of f R s with H appl for perpendicular and parallel configurations has been attributed to two competing factors of H appl induced enhancement of inductive part and H appl enhanced spin dependent transport causing fast relaxation processes in the sample. For x ¼ 0.1 composite, in both configurations of H appl , f R s is shifting towards high f region, which has been discussed in terms of dominant role of spin dependent transport. V

Advanced Materials Proceedings, 2017

Journal of Physics: Conference Series, 2019

Indian Journal of Physics, 2020

Formations of complex structures observed during the instability instigated expanding capacitive ... more Formations of complex structures observed during the instability instigated expanding capacitive mode of RF discharge in a linear vacuum vessel, in the absence of an externally applied magnetic field or any other additional constraint applied. Systematic measurements of the plasma parameters, using multiple probe diagnostics, carried out to investigate the parametric dependence of sheath development reveal visible cylindrical tube like multiple double-layer formations around a mesh-type cylindrical plasma source. Such firetube formations provide many interesting and vital information on expanding radio frequency (RF) plasma sheath, charge particle trapping and the associated sheath instability with the RF discharge. The sheath structures, glowing spot formations, space charge formations, complex structure and firetube formations in the expanding plasma are some of the features discussed here in relation to such an expanding RF discharge. Low-frequency sheath instabilities are also observed in connection to the firetube formations using a coaxial mesh-type cylindrical plasma source powered at an operating frequency of 13.56 MHz. The ion acoustic frequency-dominated instability is identified as a sheath-plasma instability associated with the RF plasma.

Journal of Molecular Liquids, 2020

Temperature dependent optical properties like birefringence, temperature gradients of refractive ... more Temperature dependent optical properties like birefringence, temperature gradients of refractive indices, molecular polarizabilities, effective geometry parameter, order parameter and cross over temperatures have been investigated for nine different liquid crystal mixtures. These mixtures are prepared by mixing two pure nematic liquid crystal compounds, namely, 4-n-pentyl phenyl 4-n′-hexyloxybenzoate (ME6O.5) and 4-cyanophenyl 4′n-pentyl benzoate (CPPB) where, ME6O.5 is a monotropic compound and CPPB is an enantiotropic compound. The mixtures however are found to be exhibit induced smectic phases. The theoretical fitting values obtained by using Hallers' extrapolated method of birefringence values agree quite well with the experimental values. It is observed that the normalized polarizability behaves exactly as refractive indices when it is plotted against temperature. The effective geometry parameter (α eg) of the mixture having highest birefringence shows highest value of α eg at certain temperature. Finally, order parameters of the mixtures have been calculated using five different techniques and for all mixtures the order parameters shows characteristics range from 0.3-0.9. The abrupt changes in order parameter before nematic phases are due to the existence of the induced smectic phases in the liquid crystal mixtures.

The European Physical Journal B, 2019

Abstract We report electrical and magneto-transport properties of La0.7Sr0.3MnO3(LSMO)/Paraffin w... more Abstract We report electrical and magneto-transport properties of La0.7Sr0.3MnO3(LSMO)/Paraffin wax nanocomposites prepared through low temperature chemical pyrophoric reaction process. A core shell structure is expected to be formed having a ferromagnetic LSMO core and a spin disordered shell of paraffin wax. Enhanced charging energy due to coulomb blockade contribution with increasing paraffin wax is observed for the composites attributing enhanced intergranular distance between LSMO grains. Effective spin-polarized tunneling of conduction electrons resulting in sharp low field magnetoresistance (MR) of the composites is due to reordering of spin disorder at paraffin wax shell with magnetic field. Moreover, observation of enhanced magnetoresistive hysteresis with decrease in temperature has been attributed to increased blocked states at LSMO grain surface. Calculated surface spin susceptibility (χb) has been found to follow similar behavior of MR with temperature indicating surface magnetization dependent MR. Fitting of magnetoconductance versus field curves reveal increase of Para to ferro transition temperature, TC and χb indicate higher antiferromagnetic coupling of shell spins for composite samples than pristine LSMO above 50 K. χb also indicate systematic decrease in surface spin disorder of the composite samples with respect to pure LSMO which is expected to be due to the probable covalent bond formation between Paraffin wax molecules and surface atoms of LSMO nanoparticles. Graphical abstract

Journal of Alloys and Compounds, 2019

Magnetoelectric coupling, magnetoimpedance and dielectric properties are investigated for spincha... more Magnetoelectric coupling, magnetoimpedance and dielectric properties are investigated for spincharge dependent magnetoelectric LaFeO 3-poly(vinylidene fluoride) hybrid nanocomposites. The X-ray diffraction pattern indicates that both LaFeO 3 and poly(vinylidene fluoride) phases coexist in the nanocomposites. The magnetoelectric coupling measurement confirms the multiferroic in nature of the nanocomposites. Magnetoelectric and magnetocapacitance (~ 42%) effects are ascribing the improvement of space charge polarization of nanocomposites. The light of classical electrodynamics causes the room temperature magnetoimpedance effect (~ 94%). Temperature dependent ac conductivity suggests the observation of negative temperature coefficient resistance behavior that also obeys the single Jonscher's power law. The conduction mechanism of the system is controlled through small and large polaronic hopping. Activation energy of those polymer based hybrid nanocomposites is estimated using Arrhenius relation. The magnetoelectric coupling of the nanocomposites is enhanced with an increase in poly(vinylidene fluoride) content. The inorganic-organic based nanocomposites could be a favorable candidate for improvement of magnetoelectric devices, smart energy storage and energy harvesting device applications.

Optical Materials, 2018

The temperature dependent properties of three liquid crystals (LC) namely effective geometry para... more The temperature dependent properties of three liquid crystals (LC) namely effective geometry parameter, order parameter and temperature gradients of refractive indices of two fluorinated isothiocyanato nematic liquid crystal (NLC) compounds 4′-pentylcyclohexyl-3,5-difluoro-4-isothiocyanatobiphenyl, 4'−butylcyclohexyl−3, 5− difluoro− 4− isothiocyanato-biphenyl of high clearing temperature (T C) and low T C LC compound 4 (trans-4 /-n-hexycyclohexyl) isothiocyanatobenzene (6CHBT) have been studied. In this paper, the effective geometry parameters of the three LC compounds are calculated. The order parameters of three LC compounds are also calculated from the effective geometry parameter. From the available data, it is found that the two fluorinated NLC compounds exhibit moderately high value of birefringence (∼0.24-0.26) and 6CHBT exhibits a lower value of birefringence (∼0.16). From the study, it is found that the order parameter is found to be higher in higher birefringence and higher T C LC compounds. The values of temperature gradient of ordinary refractive index (dn o /dT) are found to be showing negative to positive value while increasing temperature which gives the crossover temperature (T CO). The crossover temperature has been calculated from the temperature gradient at the value (dn o /dT) = 0. LC compounds with lower T C are found to have larger T CO value which gives narrower temperature between T CO and T C. The T CO value of compound having larger alkyl group is found to be smaller. The Lorentz field factors for both compound are also reported which can be used for order parameter calculation by different aspects.

International Journal of Modern Physics B, 2018

We have investigated strain mediated magnetoelectric (ME) coupling and impedance properties in 0.... more We have investigated strain mediated magnetoelectric (ME) coupling and impedance properties in 0.5Zn[Formula: see text]Ni[Formula: see text]Fe2O4–0.5HoMnO3 nanocomposites at room-temperature. The ME voltage is measured in both longitudinal and transverse direction at a frequency of 173 Hz. The impedance, real and imaginary parts of impedance and dielectric constant have been carried out in presence of DC magnetic field. With the application of magnetic field, slight decrease in dielectric constant has been observed. The impedance, real and imaginary parts of impedance are found to increase with the increase in the applied magnetic field. Nyquist plots have been fitted using three parallel combinations of resistances–capacitance circuits. Fitted parameters show the dominant role of grain boundaries, grains and interface of two types of grains of the sample.

DAE SOLID STATE PHYSICS SYMPOSIUM 2018, 2019

Dysprosium-substitution induced effects on the structural, dielectric and magnetic properties of ... more Dysprosium-substitution induced effects on the structural, dielectric and magnetic properties of CoFe 2 O 4

DAE SOLID STATE PHYSICS SYMPOSIUM 2018, 2019

We have investigated complex impedance spectroscopy and magnetoresistance(MR) of 99.5% La 0.7 Sr ... more We have investigated complex impedance spectroscopy and magnetoresistance(MR) of 99.5% La 0.7 Sr 0.3 MnO 3 (LSMO)-0.5% Glass nanocomposite material. We suppose, thin Glass boundary is formed at LSMO surface where depinning of grain boundary(GB) domain walls take place, from GB pinning centres, on application of magnetic field(H). Moreover, on application of temperature, conducting electrons at glass interface gain more thermal energy which also lead to temperature dependent electrical relaxation of the system. However the composite become more insulating on glass addition due to presence of intergranular glass barrier between neiboring LSMO grains. But surprisingly, MR of the composite indicate formation of very efficient spin polarized tunnel barrier on addition of glass at room temperature.

Journal of Molecular Liquids, 2019

In this study, we have chosen a room temperature nematic liquid crystal (NLC) compound namely, 6C... more In this study, we have chosen a room temperature nematic liquid crystal (NLC) compound namely, 6CHBT [trans-4'-n-hexylcyclohexyl) isothiocyanatobenzene] having clearing temperature at 42.8°C. This particular liquid crystal (LC) exhibits a broad nematic phase from 13°C to 42.8°C. Among all the available spectroscopy techniques, Raman spectroscopy is one of the most convenient technique to understand the various phase transitions of a LC compound. In order to understand the phase change and the change of the molecular orientations along with their change in the chemical bond, the temperature dependent Raman study has been conducted for the LC compound 6CHBT. The transition temperatures of various phases obtained from the linewidth peak positions of Raman spectra agrees well with the literature data. From the Raman spectra, the change in chemical bonds are observed which is due to the increase in the molecular orientation of the alkyl chain in the LC compound. The bond assignment of the experimental value agrees well with the Raman assignment obtained from literature. 1. Introduction: Liquid crystals (LCs) are known for their incredible behaviour and found intermediate between a solid crystalline state and an isotropic liquid state. LCs are anisotropic in nature and have anisotropic optical, electrical and magnetic properties. Because of this anisotropic property, they find a wide applicability in electro-optic devices. The molecules in the LCs are oriented in a particular direction of the LC plane, known as the director. Due to its tremendous orientational properties with respect to the director, LCs are widely used in display devices. Some of the LCs show the first order and second order non-linear optical properties and for these properties, it is industrially used in non-linear optical devices [1-7].

Materials Chemistry and Physics, 2019

Nanocomposites of xNiFe 2 O 4-(1-x)ZnO (x = 0.2, 0.3 and 0.5) have been prepared through chemical... more Nanocomposites of xNiFe 2 O 4-(1-x)ZnO (x = 0.2, 0.3 and 0.5) have been prepared through chemical "pyrophoric reaction process". Structural characterizations confirm the formation of both NiFe 2 O 4 and ZnO phases in nanocomposites. The room temperature magnetoelectric coupling, dielectric and temperature dependence of electrical properties of the prepared nanocomposites have been investigated. The observed magnetoelectric coupling may be owed to the field dependent magnetostriction property of the piezomagnetic phase of the nanocomposites. The magnetoelectric voltage is measured in both transverse and longitudinal directions. Electrical transport studies are carried out using an ac impedance spectroscopy and dc resistivity techniques. Metal-semiconductor transition of the nanocomposites has been explained on the light of delocalized and localized charge carrier. Detailed analysis of ac conductivity with frequency at varying temperature suggests the thermally activated electronic transport conduction mechanism for large and small polaronic hopping in the nanocomposites. The semiconducting band gap of the nanocomposites has also been estimated using recorded absorbance spectra. Light-dependent current-voltage characteristics are non-Ohmic in nature and exhibit significant electrical memory effect with resistive switching. On light illumination, there is a significant decrement in current with quenching of hysteresis loop suggesting high recombination of the photo-generated carriers.

Journal of Magnetism and Magnetic Materials, 2019

Room temperature magnetoimpedance and magnetodielectric effects for (100 − x)% LaFeO 3 − x% organ... more Room temperature magnetoimpedance and magnetodielectric effects for (100 − x)% LaFeO 3 − x% organic paraffin wax (x = 0, 0.5, 1, 1.5%) hybrid nanocomposites have been investigated. The enhancement of magnetoimpedance (∼226%) and magnetodielectric (∼75%) effects at low frequency region are obtained for x = 0.5% nanocomposites for strain mediation of piezomagnetic materials. The observed currentvoltage characteristics both in absence and presence of magnetic field at room temperature have corroborated with the enhanced effect. It is also showing electrical memory effect with electrical switching. The Nyquist plots have been fitted considering the parallel combination of resistance-constant phase element circuit. AC electrical studies reveal the conduction mechanism in the system controlling through the grain and grain boundaries of nanocomposites. The minimum grain and grain boundaries resistance are found for x = 0.5% nanocomposites. The electric modulus of these nanocomposites has been studied to separate the grain and grain boundaries contributions of the system. A phenomenological model has been demonstrated to explain the observed result considering the barrier width of paraffin wax layer across the grain boundaries of LaFeO 3 nanoparticles. The observed transport behavior attributes the phenomenological model. The organic hybrid nanocomposites (x = 0.5%) may be worked as a resistance-capacitance-inductance circuit with voltage magnification.

Journal of Materials Science: Materials in Electronics, 2019

Effect of particles size on the behavior of magnetoimpedance, magnetodielectric and detailed elec... more Effect of particles size on the behavior of magnetoimpedance, magnetodielectric and detailed electrical properties of structural characterized LaFeO 3 nanoparticles prepared through chemical 'pyrophoric reaction' technique having particles size of ~ 21, 43 and 51 nm have investigated. Dielectric constant of these nanoparticles gives the evidence of space charge polarization in the sample at lower frequency regime. Maximum magnetodielectric effect is obtained to ~ 61% at room temperature for particle size of ~ 21 nm, which may be due to the large surface to volume ratio of this nanoparticles compared to other particles size attributing the enhancement of space charge polarization. The maximum value of magnetoimpedance is found to ~ 92% for ~ 21 nm nanoparticle at room temperature. Magnetic field and frequency dependence room temperature magnetoimpedance are decreased with particles size of the nanoparticles. This behaviour has been explained through the light of classical electrodynamics, which reveals that this effect is depending on the magnetic field and ac signal frequency. Impedance spectroscopy is employed to study the electrical transport properties of the samples considering an equivalent circuit model for the effect of nanometric grain size. The electrical relaxation process of these materials is temperature dependent. Furthermore, ac conductivity curves follow the Jonscher's power law for electrical conduction process of the system through polaronic hopping.

Physics of Plasmas, 2018

Intensely luminous double layers develop and then expand in size in a visibly glowing RF discharg... more Intensely luminous double layers develop and then expand in size in a visibly glowing RF discharge produced using a plasma source consisting of a semi-transparent cylindrical mesh with a central electrode, in a linear plasma chamber. Although RF discharge is known to be independent of device geometry in the absence of magnetic field, the initiation of RF discharge using such a plasma source results in electron drift and further expansion of the plasma in the vessel. The dynamics of complex plasma structures are studied through electric probe diagnostics in the expanding RF plasma. The measurements made to study the parametric dependence of evolution of double layer structures are analyzed and presented here. The plasma parameter measurements suggest that the complex potential structures initially form with low potential difference between the layers and then gradually expand producing burst oscillations. The present study provides interesting information about the stability of plasma sheath and charge particle dynamics in it that are important to understand the underlying basic sheath physics along with applications in plasma acceleration and propulsion.

Materials Letters, 2018

Room temperature magnetoelectric coupling, magnetic field dependent dielectric and ac electrical ... more Room temperature magnetoelectric coupling, magnetic field dependent dielectric and ac electrical properties of xLa 0.7 Sr 0.3 MnO 3-(1 À x) Poly(vinylidene fluoride) (x = 0.5, 0.6 and 0.7) nanocomposites have been investigated. The magnetoelectric voltage coefficients are found to 0.25and0.25 and 0.25and0.16 mV/cmOe for transverse and longitudinal configurations. Dielectric constants for all the compositions are increased with increase in magnetic field. Magnetodielectric value is estimated to $16% due to the magnetostriction property of the samples. The fitted value of Nyquist plots reveals the dominant role of the grain boundaries of La 0.7 Sr 0.3 MnO 3 nanoparticles and modified grain boundaries due to Poly(vinylidene fluoride) in the samples. With the application of magnetic field the relaxation frequencies are shifted towards the higher frequency region attributing to the magnetic field dependent relaxation process in the system.

Journal of Alloys and Compounds, 2017

Magnetoelectric coupling, dielectric and electrical properties of xLa 0.7 Sr 0.3 MnO 3-(1−x) Pb (... more Magnetoelectric coupling, dielectric and electrical properties of xLa 0.7 Sr 0.3 MnO 3-(1−x) Pb (Zr 0.58 Ti 0.42)O 3 (x = 0.05 and 0.1) multiferroic nanocomposites

Journal of Molecular Liquids, 2016

Study of optical texture of different mesophases and phase transition temperatures of the liquid ... more Study of optical texture of different mesophases and phase transition temperatures of the liquid crystal compound 4,4′-din -heptyloxy-azoxy benzene has been carried out by using optical polarizing microscope. Enthalpy values and the phase transition temperatures have also been conducted by DSC studies. The variation of refractive indices with temperature has been measured by a thin prism technique using He-Ne laser and temperature dependent birefringence is calculated which shows a moderate value. Validation of the modified four-parameter model based on Vuks approximation has been carried out and reported in this article. The most important characteristics of LC compound namely macroscopic and microscopic order parameter have been evaluated by using direct extrapolation method and modified Vuks method based on Haller's extrapolation respectively. Temperature gradients of refractive indices have also been calculated. Further the normalized polarizabilities for extraordinary and ordinary rays and their ratio have been reported in this paper.

Journal of Applied Physics, 2015

Detailed magnetically tunable ac electrical properties of x La 0.7 Sr 0.3 MnO 3 (LSMO)-(1 À x) Er... more Detailed magnetically tunable ac electrical properties of x La 0.7 Sr 0.3 MnO 3 (LSMO)-(1 À x) ErMnO 3 (EMO) (x ¼ 0.1, 0.3, and 0.5) multiferroic nanocomposites have been studied at 300 K in presence of varying magnetic field (H appl), applied both in parallel and perpendicular configuration with respect to the measuring electric field. AC electrical properties have exhibited significant variation with H appl for all composites, whereas for parallel configuration of H appl such effect is very feeble for x ¼ 0.3 composite. We have attributed this anisotropic behavior to the demagnetization effect in the sample. In contrast, for x ¼ 0.1 and 0.5 composites, no such anisotropy effect is experimentally evidenced. Impedance and real part of impedance have been found to decrease with H appl at low frequency (f) region. We attribute this observation to the depinning of the magnetic domain walls from the grain boundaries pinning centers and thereby enhancing the spin dependent transport in the composite. For x ¼ 0.3 composite, Nyquist plots have been fitted considering dominant contributions of LSMO and EMO grain boundaries and the interface region between them. However, for x ¼ 0.1 composite, it corresponds to EMO grain boundaries and grain boundary interface region. The relaxation frequency (f R) is observed to shift at higher/lower f region in perpendicular/parallel configuration of H appl for x ¼ 0.3 composite. This opposite variation of f R s with H appl for perpendicular and parallel configurations has been attributed to two competing factors of H appl induced enhancement of inductive part and H appl enhanced spin dependent transport causing fast relaxation processes in the sample. For x ¼ 0.1 composite, in both configurations of H appl , f R s is shifting towards high f region, which has been discussed in terms of dominant role of spin dependent transport. V