Magneto-transport Properties of La_(0.80)Sr_(0.20)Mn_(1−x)Cu_xO_3 Thin Films Fabricated by Using Spray Pyrolysis

Pawan Kumar,Rakesh Kumar Dwivedi,Pawan Kumar,Ravikant Prasad,Praveen Kumar Siwach,Hari Krishna Singh 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.1

Thin films of La_(0.80)Sr_(0.20)Mn_(1−x)Cu_xO_3 with x = 0.00, 0.04, 0.08, 0.10, 0.15, and 0.20 were deposited on single-crystal LaAlO_3 (100) (LAO) substrates at 250 ± 10 ℃ by using a nebulized spray pyrolysis technique. Structural, surface, and transport characterizations were done by X-ray diffraction (XRD), atomic force microscopy (AFM) and the standard four probe technique, respectively. XRD patterns revealed the formation of single-phase polycrystalline films with a rhombohedral crystal structure. Cu substitution resulted in a uniform decrease in the metal insulator transition (T_(IM)) temperature up to x = 0.10, followed by a drastic decrease in T_(IM) for x = 0.15. Finally, the metal-insulator transition vanished for higher Cu concentrations (x = 0.20) in the observed temperature range. The variation in T_(IM) with the amount of added Cu is explained on the basis of the double exchange mechanism. Cu substitution has been found to perturb the Mn^(3+)-O-Mn^(4+) network and has a strong influence on T_(IM). The variation in resistivity maxima with temperature for different Cu concentrations showed a systematic trend up to x ∼ 0.10. We also explored the electrical conduction at T > T_(IM) in the framework of small polaron hopping in the adiabatic limit. The activation energy showed a strong dependence on the Cu concentration. The maximum magneto-resistance (MR) up to 10%, was observed for x = 0.15 at low temperatures.

Hybrid porous thin films: Opportunities and challenges for sensing applications

Kumar, Pawan,Kim, Ki-Hyun,Vellingiri, Kowsalya,Samaddar, Pallabi,Kumar, Parveen,Deep, Akash,Kumar, Naresh Elsevier 2018 Biosensors & bioelectronics Vol.104 No.-

<P><B>Abstract</B></P> <P>In this paper, the scientific progress in the field of thin film materials and their associated sensing technologies are described comprehensively to address the directions for future research and developments as per the need of modern-day technologies. To begin with, we briefly discussed the fundamental synthesis approaches for advanced thin films with an emphasis on the properties necessary for controlled fabrication (e.g., the elemental ratio and spatial arrangement). Subsequently, we explored the control, characterization, and optimization of hybrid porous thin films with respect to diverse sensing applications. The application of hybrid porous thin film materials has also been discussed in relation to the mechanisms used for biological, optical, electrical, acoustic, and other advanced sensing techniques (e.g., surface-enhanced Raman scattering (SERS)). Finally, conclusions are drawn to highlight the current status of thin film-based sensing technology along with its opportunities and challenges.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fundamental synthesis approaches of advanced thin films. </LI> <LI> Here optimization of hybrid porous thin films for advanced sensing techniques is reviewed. </LI> <LI> Current status, opportunities, and challenges are discussed. </LI> </UL> </P>

Anomalous Weak Ferromagnetism in Electron-doped Nd_(1−x)Sr_xMnO_3 (0.50 ≤ x ≤ 0.62) Thin Films

Pawan Kumar,Ravikant Prasad,Hari Krishna Singh,Rakesh Kumar Dwivedi,Avanish Kumar Srivastava,Mangala Prasad Singh 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.4

In the present work we demonstrate that an anomalous weak ferromagnetism occurs in the composition range 0.50 ≤ x ≤ 0.62 in nanostructured thin films of Nd_(1−x)Sr_xMnO_3 (NSMO). Nanocrystalline thin films of overdoped manganite Nd_(1−x)Sr_xMnO_3 (<I>x</I> ∼ 0.50, 0.55, 0.60 and 0.62) on single crystal LaAlO_3 (001) substrates are grown by nebulized chemical spray pyrolysis technique. These single phase films possess average crystallite size ∼15 nm and the width of the grain boundaries is ∼1 - 2 nm. In the composition range 0.50 ≤ x ≤ 0.62, the ground state of NSMO is A-type antiferromagnetic (AFM) metallic. However, in the present films a broad paramagnetic (PM) to ferromagnetic (FM) transition is observed in all the compositions at T_C ∼ 226 K for x = 0.50 and 235 K for rest of the samples. All the films show a well-defined M-H hysteresis loop at 5 K. The coercivity (H_C) of these films is much larger than those having composition range 0.35 < x < 0.45. For x = 0.50 (0.62) film H_C = -1210 (-1484) Oe and +1162 (+1476) Oe. The asymmetry in coercivity suggests the presence of weak exchange bias effect in these films. It is observed that the FM ground state in these films have smaller magnetic moment per Mn atom than the expected full moment using the rigid model, we term this as a weak ferromagnetic (WFM) state arising due to the destabilization of the AFM ordering. We propose a possible scenario based on the combined effect of spin reorganization and enhanced orbital disordering in nanosized manganites, to explain the observed anomalous weak ferromagnetism in the A-type AFM spin ordered regime.

A novel method for controlled synthesis of nanosized hematite (α-Fe2O3) thin film on liquid-vapor interface

Kumar, Pawan,Singh, Raj Kumar,Rawat, Nitin,Barman, Partha Bir,Katyal, Subhash Chander,Jang, Hwanchol,Lee, Heung-No,Kumar, Rajesh Springer-Verlag 2013 Journal of nanoparticle research Vol.15 No.4

On stability of Banach frames

Pawan Kumar Jain,Shiv Kumar Kaushik,Lalit Kumar Vashisht 대한수학회 2007 대한수학회보 Vol.44 No.1

ON STABILITY OF BANACH FRAMES

Jain Pawan Kumar,Kaushik Shiv Kumar,Vashisht Lalit Kumar Korean Mathematical Society 2007 대한수학회보 Vol.44 No.1

Some stability theorems (Paley-Wiener type) for Banach frames in Banach spaces have been derived.

Temporal multifractal analysis of extreme events in the crude oil market

Devi Pooja,Kumar Sunil,Kumar Pawan,Kumar Sushil,Khan Imran,Kumar Pawan 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.4

The ‘crude oil price’ has been one of the integral components of rising globalization. This paper delves into the static and dynamic multifractal analysis of daily prices of Brent crude oil for the period of 33 years (1987–2020) using the multifractal detrended fuctuation analysis. We discuss the results and limitations of the static multifractal analysis of historical data of crude oil. The crude oil market contains much more complexity in its dynamics that needs to be examined to draw inferences. These are important for socio-economic and political policy formulation at the global level. Thus the temporal multifractal analysis of historical data of crude oil is performed to understand such complexity. Further, the efect of extreme events on the multifractal properties of the crude oil market is also investigated. It is shown that multifractal spectra evolve through diferent shapes with time and the multifractal asymmetry coefcient can be used as an indicator in the detection of extreme events.

A geo-spatial inter-relationship with drainage morphometry, landscapes and NDVI in the context of climate change: a case study over the Varuna river basin (India)

Pawan Kumar Chaubey,Arnab Kundu,R. K. Mall 대한공간정보학회 2019 Spatial Information Research Vol.27 No.6

Watershed development and management is essential for the present as well as future constancy of water resources in a river basin. Watershed prioritization, planning and development are depending on the morphometric analysis of a basin. The drainages of a basin are mainly influenced on geomorphic appearances which show a dynamic role for monitoring the basin’s hydrology as per topographical characteristics. In this paper, the morphometric study was characterized by set of parameters i.e. linear, aerial and relief aspects of Varuna river basin (India) with the integration of geo-spatial techniques. The mean annual rainfall, Normalized Difference Vegetation Index, Digital Elevation Model and Land Use/Land Cover (LULC) were taken into account for this study. The annual rainfall pattern and its percentage departure were shown by high frequencies of drought conditions while the seasonality index depicts that mostly rainfall occurred in less than 3 months. Moreover, indices such as Standardized Precipitation Index and Standardized Precipitation Evapotranspiration Index were used to conclude past extreme drought conditions (1996–2002, 2010–2017) over the basin. LULC changes were monitored over the south-east and north-west part of river basin during the period 1977 to 2013. The results revealed that an increasing trend of urbanization was monitored due to a decrease in agricultural land by 40.71% in the lower part of the basin. Moreover, the overall study can be helpful to assess the quantitative depiction of basin geometry as well as land use pattern for future development of agricultural growth.

Moisture management behaviour of modified polyester wool fabrics

Pawan Kumar,Sujit Kumar Sinha,Subrata Ghosh 한국의류학회 2015 Fashion and Textiles Vol.2 No.1

To support the thermo regularity system of human body in completely changed environment and physical activity the functional clothing must create a stable microclimate next to the skin. The present study deals with the moisture transport and moisture management behaviour of polyester wool yarn and knitted fabric treated with two types of enzyme viz; alkaline protease enzyme and acidic protease enzyme. The prime object of this study was to enhance the moisture transport and moisture management properties of yarn and fabric for use in active wear. The results reveal superior wicking behaviour by alkaline protease enzyme treatment, while superior moisture vapour permeability with acidic protease enzyme treatment. Moisture management properties of alkaline protease enzyme treated fabric gives better result, ranging its grade from very good to excellent with higher absorption rate, one way transport capacity and spreading speed. Analysis of variance (ANOVA) was applied to test statistical significance level of all effects.

Metal organic frameworks (MOFs): Current trends and challenges in control and management of air quality

Pawan Kumar,Eric Vejerano,Azmatullah Khan,Grzegorz Lisak,안정현,김기현 한국화학공학회 2019 Korean Journal of Chemical Engineering Vol.36 No.11

Coordination polymers (CPs) are a unique class of polymers characterized by a molecular structure consisting of repeating metal centers linked by organic ligands in an infinite array connected through coordination bonding. In the last two decades, research interest in CPs, such as metal organic frameworks (MOFs), has grown rapidly owing to their exclusive advantageous properties (e.g., exceptionally high surface area, chemical and thermal stability, molecular functionality, porosity, electron mobility, thermal conductivity, and mechanical strength). In this study, we started with a basic question: Why and how are coordination polymers special and how do they differ from other classes of polymers? Next, we explored the value of unique and innovative CPs in line with the advent of design and synthesis approaches. We focused on the current trends and challenges of CPs/MOFs for application in the control and management of air quality. The intent of this review is to motivate development of CPs/MOFs that can be ultimately applied towards more efficient and effective technology as remediating and managing of the air quality. Ultimately, this review will help us open a new paradigm to pursue the future progress in polymers and materials science that targets specific applications in environmental engineering.