Manvendra Singh Khatri - Academia.edu (original) (raw)

Papers by Manvendra Singh Khatri

Journal of Physics: Conference Series, Nov 30, 2023

Research Square (Research Square), May 7, 2024

Cu-Ni-W thin films are deposited by varying the current density from-5 to-60 mA/cm² using the gal... more Cu-Ni-W thin films are deposited by varying the current density from-5 to-60 mA/cm² using the galvanostatic chronopotentiogram method on ITO-coated glass substrates. The X-ray diffraction (XRD) analysis revealed that Cu-Ni-W thin films exhibit a face-centered cubic structure with the presence of specific crystallographic planes, particularly (111), (200), and (220), at 2θ values of 43.4°, 50.7°, and 74.7°. The additional peaks observed at other 2θ values correspond to NiW and Ni4W phases. It is found that film deposited at higher current densities favor the growth of smaller crystalline size of 17 nm and higher degree of texture coefficient of 2.48. The maximum value of micro-strain of about 16% is calculated from the peak broadening of X-ray diffractograms. Due to the strong (111) texture and nano crystallites as confirmed by XRD resulted in an outstanding corrosion resistance of 16.22 kΩ cm² for the film deposited at-60 mA/cm².

Protection of Metals and Physical Chemistry of Surfaces

Thin films and nanowires of Co-Pt have been prepared by means of electrodeposition. Composition, ... more Thin films and nanowires of Co-Pt have been prepared by means of electrodeposition. Composition, structure, microstructure and magnetic properties have been intensively studied using X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry and correlated to the deposition parameters such as electrolyte composition, deposition current and/or potential. Co rich Co-Pt films have been deposited at various current densities. A nearly constant composition of Co 70 Pt 30 was achieved for current densities between 18 and 32 mA/cm². Detailed texture measurements confirmed an increasing fraction of the hexagonal phase with its c-axis aligned perpendicular to the film plane with increasing current density. Accordingly, magnetic properties are strongly affected by the magnetocrystalline anisotropy of the hexagonal phase that competes with the shape anisotropy of the thin film geometry. Co-Pt nanowires have been prepared within alumina templates at different deposition potentials between-0.6 and-0.9V SCE changing the composition from nearly pure Pt to Co. The composition Co 80 Pt 20 was observed at a deposition potential of-0.7V SCE. Co-Pt nanowires are nanocrystalline in the as-deposited state. Magnetic measurements reveal changing fcc and hcp phase fractions within the wires as the effective anisotropy significantly differs from the expected shape anisotropy for nanowires with high aspect ratio. This change in effective anisotropy is attributed to the preferential alignment of the c-axis of hcp Co-Pt phase perpendicular to the nanowires axis. A promising alternative with much smaller feature sizes is the diblock copolymer template. Electrodeposition of Co and Co-Pt into these templates has been carried out. Inhomogeneities in the template thickness as well as a certain substrate roughness have been identified to be the reasons for inhomogeneous template filling. Thus magnetic properties are dominated by large deposits found on top of the template. Additionally, rolled-up tubes of several nm thick Au/Co/Au films have been characterized magnetically. Temperature dependent measurements show an exchange bias behaviour that is explained in terms of induced stresses during cooling. Changes of magnetic properties in the investigated samples are finally discussed in terms of competing effects of different magnetic anisotropies in various geometries. Kurzfassung Co-Pt Dünnschichten und Nanodrähte wurden mittels elektrochemischer Abscheidung hergestellt. Zusammensetzung, Struktur, Mikrostruktur und magnetische Eigenschaften wurden intensiv mit Röntgenbeugung, Rasterelektronenmikroskopie und Magnetometrie untersucht und mit den Depositionsparametern wie Elektrolytzusammensetzung, Abscheidestrom und/oder-potential korreliert. Co reiche Co-Pt-Filme wurden mit verschiedenen Stromdichten hergestellt. Eine nahezu konstante Zusammensetzung im Bereich Co 70 Pt 30 wurde für Stromdichten zwischen 18 und 32 mA/cm² erreicht. Detaillierte Texturmessungen bestätigen einen zunehmenden Anteil an hexagonaler Phase mit senkrecht zur Filmebene ausgerichteter c-Achse mit zunehmender Stromdichte. Dementsprechend werden die magnetischen Eigenschaften stark von der magnetokristallinen Anisotropie der hexagonalen Phase beeinflusst, die mit der Formanisotropie der Dünnschicht-Geometrie konkurriert. Co-Pt-Nanodrähte wurden in nanoporöse Aluminiumoxidmembranen bei verschiedenen Potentialen zwischen-0,6 und-0.9 V SCE abgeschieden, wobei sich die Zusammensetzung von nahezu reinem Pt zu Co verändert. Die Zusammensetzung Co 80 Pt 20 wurde bei einem Abscheidepotential von-0.7 V SCE erhalten. Die so hergestellten Co-Pt Nanodrähte sind nanokistallin. Magnetische Messungen weisen jedoch auf veränderte Phasenanteile der fcc und hcp Phase innerhalb der Drähte hin, da die effektive Anisotropie erheblich von der für Nanodrähte mit hohem Aspektverhältnis erwarteten Formanisotropie abweicht. Diese Änderung der effektiven Anisotropie ist auf die bevorzugte Ausrichtung der hexagonalen c-Achse des Co-Pt senkrecht zur Drahtachse zurückzuführen. Vielversprechende Template mit deutlich kleineren Dimensionen sind Diblockcopolymertemplate. Es wurden Versuche zur Abscheidung von Co und Co-Pt in diese Template durchgeführt. Als Gründe für die inhomogene Templatfüllung wurden Inhomogenitäten in der Schichtdicke sowie eine gewisse Rauhigkeit der Substrate identifiziert. Aufgrund der ungleichmäßigen Fülleg werden die magnetischen Eigenschaften durch große, halbkugelförmige Abscheidunge auf der Oberfläche des Templates bestimmt. Darüber hinaus wurden aus wenige nm dicken Au/Co/Au Filmen hergestellte Mikroröhren magnetisch charakterisiert. Temperaturabhängige Messungen zeigen ein Exchange Bias Verhalten, das durch beim Abkühlen induzierte Spannungen erklärt wird. Unterschiede im magnetischen Verhalten der untersuchten Proben werden abschließend im Hinblick auf die verschiedenen konkurrierenden magnetischen Anisotropien in verschiedenen Geometrien diskutiert. 6 Magnetic properties of rolled-up microtubes ……………………………………….87 6.1 Motivation ……………………………………………………………………87 6.2 Fabrication of rolled-up microtubes ………………………………………….87 6.3 Magnetic measurements ……………………………………………………..90 Summary and outlook ………………………………………………………………….95 References ……………………………………………………………………………....99 Publication list.…………………………………………………………………………106 Acknowledgements …………………………………………………………………....107 with the different crystallographic structures of Co-Pt allows tuning the magnetic properties. A systematic variation of deposition conditions will be used to control composition and aspect ratio of the Co-Pt nanowires, which results in a large variation of their magnetic properties. In order to understand the influence of magnetocrystalline anisotropy in detail, temperature dependent measurements will be used. In order to obtain a further reduction of the nanowire's extensions, diblock copolymer templates with a pore diameter of about 8 nm will be used (chapter 5). Approaches to fill these templates with Co and Co-Pt are given. These templates offer an attractive route to fabricate nanoscaled structures, since they spontaneously form a range of well-defined, well-ordered structures including spheres, cylinders and lamellae 7. For

Computational and Applied Mathematics

In this study, an attempt has been made to formulate a novel SEIAHR deterministic compartmental m... more In this study, an attempt has been made to formulate a novel SEIAHR deterministic compartmental model for the COVID-19 pandemic by incorporating additionally vaccinated and quarantined compartments. We obtained the basic reproduction number using the next-generation matrix approach. Thereafter, the stability of equilibrium points has been investigated using the basic reproduction number. Furthermore, we have studied the pandemic behaviour in four countries: Brazil, India, Italy, and the USA. We have fitted the proposed model to daily new cases and cumulative cases of the aforementioned countries using the nonlinear least square technique in MATLAB. Moreover, we have also estimated the best-fitted model parameters based on the available data. In addition, a numerical simulation of the model has been added to examine the influence of intervention policies, vaccination rates, vaccine efficacy, and quarantine. It was found that all the control policies had a positive impact on reducing the COVID-19 incidence.

Nanotechnology, 2008

The structure and the magnetic properties of an InGaAs/Fe 3 Si superlattice in a cylindrical geom... more The structure and the magnetic properties of an InGaAs/Fe 3 Si superlattice in a cylindrical geometry are investigated by electron microscopy techniques, x-ray diffraction and magnetometry. To form a radial superlattice, a pseudomorphic InGaAs/Fe 3 Si bilayer has been released from its substrate self-forming into a rolled-up microtube. Oxide-free interfaces as well as areas of crystalline bonding are observed and an overall lattice mismatch between succeeding layers is determined. The cylindrical symmetry of the final radial superlattice shows a significant effect on the magnetization behavior of the rolled-up layers.

Co-rich Co-Pt films have been electrodeposited on Si (100) substrates with a 30 nm thick Cr buffe... more Co-rich Co-Pt films have been electrodeposited on Si (100) substrates with a 30 nm thick Cr buffer and a 10 nm Au conducting layer. Films have been deposited on different days after preparing the electrolyte, at current density of 28 mA/cm2, keeping all other deposition parameters constant. It has been observed from pole figures and magnetic measurements that the age of electrolyte has a significant effect on phase formation and magnetic properties of Co-Pt films. This instability in the deposition process with the age of the electrolyte is attributed to the anodic oxidation of ammonia and citrate in the presence of Co2+ ions, which has a significant influence on the deposition of cobalt based alloys. The reduction of Co2+ can be modify by two ways. First, it is possible that the nature of the complexation of Co2+ is changed because of a decomposition of ammonium citrate and formation of new compounds. Secondly, the new molecules formed in the anodic reaction may decrease the rate o...

Physica Status Solidi (a), 2011

ABSTRACT Co-rich Co–Pt alloy films have been grown by electrodeposition on Au buffer layer. Detai... more ABSTRACT Co-rich Co–Pt alloy films have been grown by electrodeposition on Au buffer layer. Detailed texture measurements have been performed in order to understand the dependence of magnetic properties on phase composition and texture. X-ray analysis in Bragg–Brentano geometry shows that films seem to consist of hexagonal closed packed (hcp) or fcc phase. Due to similar lattice spacing of the densely packed planes of both possible phases, the (111) fcc and (002) hcp planes of Co–Pt and also the higher order reflections coincide. As a result, the information supplied by X-ray diffraction was of limited value. Hence pole figure measurements are used which determine the directional distribution of planes with a selected spacing. Here we present an approach to use pole figure measurements for phase identification. We show that this method allow a direct correlation with the magnetic properties, in particular with the magnetocrystalline anisotropy and magnetic texture.

Applied Physics Letters, 2009

Au/Co/Au trilayers are fabricated by tilted deposition on prestructured polymer sacrificial layer... more Au/Co/Au trilayers are fabricated by tilted deposition on prestructured polymer sacrificial layers. The metal trilayers are released by selectively dissolving the sacrificial layer and roll-up into microtubes. Magnetization properties are strongly affected by the roll-up process. In addition to a modified shape anisotropy, the magnetostrictive anisotropy due to the anisotropic stress release is reversed. Low temperature measurements support the presence of significant exchange bias in these rolled-up structures.

Electrochimica Acta, 2009

Patterned media for future ultrahigh-density magnetic data storage can be prepared by electrodepo... more Patterned media for future ultrahigh-density magnetic data storage can be prepared by electrodeposition into ordered arrays of nanostructured templates. Diblock copolymer templates have been proposed as a promising alternative to alumina templates. They possess smaller feature sizes than alumina and thereby allow for higher storage densities. Templates with pore diameters of ∼8nm have been fabricated by dip-coating a conducting substrate

In this paper, we have investigated structural and magnetic properties of CoFe–Cu granular thin f... more In this paper, we have investigated structural and magnetic properties of CoFe–Cu granular thin films as a function of ferromagnetic layer pulse time (tCoFe). These films were electrodeposited on Au-coated Si substrate from an aqueous solution containing boric acid and ascorbic acid as additives. Deposition potential for Cu layer was − 0.5 V and − 0.9 V for CoFe layer with respect to (AgCl/Ag) electrode. EDX analysis has shown that ferromagnetic material concentration increases with increase in ferromagnetic layer pulse time (tCoFe). The presence of (110) (200) (211) (311) and (220) XRD reflections observed at 2θ ~ 45°, 52°, 83°, 93°, and 99° indicate that these films have mixture of body-centered cubic and face-centered cubic structure. Magnetic measurements revealed that the easy axis of magnetization lies along the in-plane direction. Magnetic properties of granular films are explained by considering the changes in the elemental composition, deposition time, dynamics of the surfa...

Proceedings of the National Academy of Sciences, India Section A: Physical Sciences

Materials Chemistry and Physics

Journal of Low Temperature Physics

CoPtP alloy nanowires,~200 nm in diameter, have been prepared by the electrode position method in... more CoPtP alloy nanowires,~200 nm in diameter, have been prepared by the electrode position method into the pores of a porous anodic aluminum oxide template. X-ray diffraction pattern shows that the wires consist of a mixture of fcc and hcp phases with CoPt (002) and CoPt (221) texture. The coercivity was found to be 1150 Oe at 50 K and 760 Oe at 300 K, when the field was applied parallel to the wire axis. The temperature dependence of coercivity was explained by considering the magneto crystalline anisotropy and thermal activation effect.