arXiv subjects

P. Sen

Publications and source records attributed to P. Sen.

7 recordsLinked to original sources

arXiv2014

Synthesis and Characterization of Nanocomposites of Fe Nanoparticles and Activated Carbon

We have synthesized the bulk form of the superparamagnetic nanocomposites of Fe nanoparticles and activated carbon. Here highly porous feature of activated carbon and magnetic properties of Fe nanoparticles were combined together to form the nanocomposites by mechanical mixing of different proportion of both of them. These nanocomposites are characterized by various characterization techniques like X-ray diffraction (XRD), transmission electron microscopy (TEM), magnetization measurement and M\"ossbauer spectroscopy. The observed XRD patterns have shown most intense peaks at 2{\theta} = 44.8 degree, which correspond to the (110) plane of the pure Fe in body centered cubic phase. Average particles sizes obtained by TEM imaging are in the range of 20 nm, which are below the required limit for Fe nanoparticles to be in superparamagnetic phase. The superparamagnetic nature of the nanocomposites together with trace amount of the ferromagnetic phase was confirmed by magnetization measurements and M\"ossbauer spectroscopy. Particles size calculated by the Langavin function fitting of the magnetization vs magnetic field curves are in qualitatively good agreement with the size obtained from TEM imaging.

cond-mat.mes-hall↗

arXiv2014

Evolution of magnetic dynamics in an artificially frustrated Fe nanoparticle system

Frustrated lattices1-3, characterized by minor breakdown in local order in an otherwise periodic lattice, lead to simultaneous possibilities of several ground states which can trigger unique physical properties, in condensed matter systems. In magnetic materials with atomic spins, frustration takes another shape with added possibilities to construct various topological arrangements of spins, whereby magnetic order is disturbed2,4. We have achieved a new approach to introduce positional atomic disorder inside a Fe nanoparticle lattice, forming domains without boundaries to study magnetic dynamics of the constituent spins. This magnetism overrides the exchange bias derived magnetic enhancement, appears only at temperatures around 200 K and is characterized by a dynamic polarity, p = +/-1 (positive or negative) with a precise frequency. The material otherwise behaves like a superparamagnet with characteristic magnetization behaviour at room temperature and 2 K.

cond-mat.mes-hall↗

arXiv2013

Room temperature operational single electron transistor on the macroscopic surface of hydrogenated diamond like carbon

This paper shows single electron transistor at room temperature,created on macroscopic system-the two-dimensional large area surface of our hydrogenated diamond like carbon thin film. Our results, free from the limitation of lowering the size of coulomb blockade in sub-nanometer range with the existing unprofitable process,are consistent with the theoretical results and will be relevant for future practical applications in the realm of atomic physics, quantum phenomenon and metrology.

cond-mat.mes-hall↗

arXiv2009

Scaling and crossover phenomena in anomalous helium sequence

Anomalous temporal fluctuations of helium concentrations in spring emanations have been observed on a number of occasions prior to some major seismic events. Several recent studies have shown that a wide variety of natural systems display significant fluctuations that may be characterized by long-range power-law correlations. We have applied detrended fluctuation analysis (DFA) to characterize preseismic helium anomalies and to probe the relationship between two classes of apparently irregular helium sequences. Application of the DFA technique reveals a crossover phenomenon that distinguishes short-range from long-range scaling exponents; the crossover corresponds to a transition from nonpersistent to persistent traits in the helium time series. Our findings imply a significant statistical correlation between anomalous helium concentration and a fluctuation exponent. This analytical approach appears to be a promising way for identifying anomalous helium fluctuations as signals precursory to an earthquake.

nlin.CD↗

arXiv2002

Hidden Translation and Translating Coset in Quantum Computing

We give efficient quantum algorithms for the problems of Hidden Translation and Hidden Subgroup in a large class of non-abelian solvable groups including solvable groups of constant exponent and of constant length derived series. Our algorithms are recursive. For the base case, we solve efficiently Hidden Translation in $\Z_{p}^{n}$, whenever $p$ is a fixed prime. For the induction step, we introduce the problem Translating Coset generalizing both Hidden Translation and Hidden Subgroup, and prove a powerful self-reducibility result: Translating Coset in a finite solvable group $G$ is reducible to instances of Translating Coset in $G/N$ and $N$, for appropriate normal subgroups $N$ of $G$. Our self-reducibility framework combined with Kuperberg's subexponential quantum algorithm for solving Hidden Translation in any abelian group, leads to subexponential quantum algorithms for Hidden Translation and Hidden Subgroup in any solvable group.

quant-ph↗

arXiv1998

Annealing of defects in Fe after MeV Heavy ion irradiation

We report study of recovery dynamics, followed by in-situ resistivity measurement after 100 MeV oxygen ion irradiation, in cold rolled Fe at 300K. Scaling behavior with microstructural density and temperature of sample have been used to establish stress induced defects formed during irradiation as a new type of sink. The dynamics after irradiation has been shown to be due to migration of defects to two types of sinks i.e. stress induced defect as variable sinks and internal surfaces as fixed sinks. Experimental data obtained under various experimental conditions have been fitted to theoretical curves. Parameters thus obtained from fitting are employed to establish effect of electronic energy loss and temperature on recovery dynamics and stress associated with variable sinks.

cond-mat.mtrl-sci↗

arXiv1997

Dissipative structure formation in cold-rolled Fe and Ni during heavy ion irradiation

We report 4-probe resistivity measurements of cold-rolled Ni and Fe during 100 MeV oxygen ion irradiation, at 300K. The resistivity shows increase and saturation, marked by jumps. Employing 200 MeV silver ion irradiation of Fe and Si(100) and topographically identifying strain at an artificial interface in the latter, we assign the resistivity behavior to atomic rearrangements arising from dissipation of incident ion energy at internal interfaces of Ni and Fe, with positive feedback.}

cond-mat↗