Jayee Sinha

Bio: Jayee Sinha is an academic researcher from University of Calcutta. The author has contributed to research in topics: Magnetic refrigeration & Beam divergence. The author has an hindex of 2, co-authored 5 publications receiving 7 citations.

Measurement protocols dependent giant magnetocaloric effect in MnNiSi-based system

Abstract: MnNiSi-based compounds exhibit giant isothermal magnetic entropy change (ΔSM) across their induced first-order coupled magnetostructural transition (MST) in the vicinity of room temperature, though in most of the cases, the use of Maxwell relation from a very frequently used but incorrect measurement protocol provides a nonphysical spike to the calculated ΔSM. Herein, to realize the accurate measurement protocol, we explore magnetocaloric properties of a (FeCoGa)x doped (MnNiSi)1−x compound with x = 0.165 rigorously. Several methods, including the estimation of ΔSM using Maxwell relation, Clausius-Clapeyron equation, and also from the calorimetry measurement, are discussed explicitly. The studied material is observed to show a MST at 265 K and a giant ΔSM as large as about −29.3 J kg−1 K−1 due to a magnetic field change of 5 T following the Maxwell equation during discontinuous cooling and field increasing mode, which enables the material as a promising candidate for magnetic refrigeration.

Design of Memristor – CMOS based logic gates and logic circuits

Abstract: Recent researches are mostly focused on technology scaling as well as device size minimization design techniques following Moore’s law. Conventional computing architectures are unable to fulfill modern application demands. Memristor is a promising alternative device which has been developed by many researchers [2] to draw attention of its structure for numerous applications which includes computational logic, memory implementations and neuromorphic systems. This paper emphasizes the basic properties of memristor at the device level. Different digital circuits have been designed for logic operations and DSP applications. Design methodologies are developed for proper circuit design, and circuit parameters are taken from a very detailed device model and optimization techniques. The transient response of Hybrid CMOS-memristor based logic gates and different adder circuits (i.e, half adder, full adder, carry-save adder) and multiplier circuit are performed in Cadence 180nm technology.

A comparative study on the performance of RESET based electro-thermal process in ring shaped confined Ge 2 Sb 2 Te 5 and Ge 1 Cu 2 Te 3 chalcogenide memory structures

Abstract: This work presents the comparative performance analysis of Ge 2 Sb 2 Te 5 (GST) and Ge 1 Cu 2 Te 3 (GCT) based phase change memory materials with ring-shaped confined chalcogenide (RCC) cell structure. Three-dimensional finite element simulation with rotational symmetry is used to analyze the electro-thermal process within the RCC cell during phase change operation. The RCC cell structures show superior performance in terms of power consumption required for phase change as compared to other reported PCRAM structures. The results indicate that during the transition from low to high resistance, GCT cell shows superior performance compared to GST cell with power consumption of 1.62 mW and 2.83 mW, respectively. Also, 42.75% reduction in power consumption has been observed in the proposed GCT cell. The GCT based RCC cell requires a relatively lower voltage of 1.75 V for phase transition in comparison to 2.55 V in a GST RCC cell of similar dimension.

Aspect ratio-based formulation for far-field characterization of single-mode trapezoidal index fibers

Abstract: We present simple and complete empirical relations to predict the angle of beam divergence in terms of normalized frequency and aspect ratio of a single-mode trapezoidal index fiber. This is done for the far-field characterization over a long range of normalized frequencies without the calculation of normalized spot sizes. On comparison, we observe an excellent match of our results with exact values establishing the validity of our formulation. The formulation should attract attention as a simple alternative to the rigorous methods of estimating the angle of beam divergence for such fibers. It can be widely used by system users and developers for much better control over far-field related calculations and experiments.

Memristive Circuit Implementation of a Self-Repairing Network Based on Biological Astrocytes in Robot Application

Abstract: A large number of studies have shown that astrocytes can be combined with the presynaptic terminals and postsynaptic spines of neurons to constitute a triple synapse via an endocannabinoid retrograde messenger to achieve a self-repair ability in the human brain. Inspired by the biological self-repair mechanism of astrocytes, this work proposes a self-repairing neuron network circuit that utilizes a memristor to simulate changes in neurotransmitters when a set threshold is reached. The proposed circuit simulates an astrocyte-neuron network and comprises the following: 1) a single-astrocyte-neuron circuit module; 2) an astrocyte-neuron network circuit; 3) a module to detect malfunctions; and 4) a neuron PR (release probability of synaptic transmission) enhancement module. When faults occur in a synapse, the neuron module becomes silent or near silent because of the low PR of the synapses. The circuit can detect faults automatically. The damaged neuron can be repaired by enhancing the PR of other healthy neurons, analogous to the biological repair mechanism of astrocytes. This mechanism helps to repair the damaged circuit. A simulation of the circuit revealed the following: 1) as the number of neurons in the circuit increases, the self-repair ability strengthens and 2) as the number of damaged neurons in the astrocyte-neuron network increases, the self-repair ability weakens, and there is a significant degradation in the performance of the circuit. The self-repairing circuit was used for a robot, and it effectively improved the robots' performance and reliability.

Large reversible magnetocaloric effect and magnetoresistance by improving crystallographic compatibility condition in Ni(Co)-Mn-Ti all- d -metal Heusler alloys

Abstract: Recently, all-$d$-metal Ni(Co)-Mn-Ti Heusler systems have become the research hotspot due to their magnetoresponsive properties associated with a tunable first-order magnetostructural transformation (MST) and excellent mechanical stability for potential applications. However, the presence of large thermal hysteresis acts as an obstacle to the cyclic operation of this novel material. In this present paper, we investigate a large reversible magnetocaloric effect (MCE) and magnetoresistance (MR) in ${\mathrm{Ni}}_{37\ensuremath{-}x}{\mathrm{Co}}_{13+x}{\mathrm{Mn}}_{34.5}{\mathrm{Ti}}_{15.5}$ all-$d$-metal Heusler alloys that undergo a first-order MST accompanied by a large magnetization change between ferromagnetic austenite and antiferromagnetic martensite phases. Tuning the small at.% of Co doping in ${\mathrm{Ni}}_{37\ensuremath{-}x}{\mathrm{Co}}_{13+x}{\mathrm{Mn}}_{34.5}{\mathrm{Ti}}_{15.5}$ systems, we achieved an optimum composition with $x$ = 1 where low thermal hysteresis of $\ensuremath{\sim}4.7$ K, a narrow transformation interval of $\ensuremath{\sim}11.2$ K, and improved sensitivity of transformation temperature $\ensuremath{\sim}2.8$ K/T is observed. In addition, the origin of small hysteresis is studied based on geometric compatibility between cubic austenite and monoclinic martensite phases, calculated from the powder x-ray diffraction data. These optimized parameters lead to a reversible magnetic field-induced inverse martensitic transition under the field cycling, yielding a large reversible magnetic entropy change ($\mathrm{\ensuremath{\Delta}}{\mathrm{S}}_{M}$) of $\ensuremath{\sim}17.78$ J ${\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at 277 K in a field change of 5 T. Moreover, a large reversible magnetoresistance (MR) of $\ensuremath{\sim}14%$ out of 32.6% is also obtained under 5-T magnetic field for $x$ = 1 sample in all-$d$-metal Heusler alloys. These reversible magnetoresponsive properties are comparable to other Ni-Mn-based Heusler alloys and have not been reported so far in the all-$d$-metal Heusler system. Therefore our present work demonstrates a pathway to design new cyclically stable multifunctional materials in all-$d$-metal Heusler systems for solid-state cooling devices and magnetic recording applications.

First-principles study and experimental characterization of metal incorporation in germanium telluride

Abstract: Germanium telluride is a well-known phase change material (PCM) used in non-volatile memory cells and radio frequency switches. Controlling the properties of GeTe for improved PCM device performance has sometimes been achieved by doping and/or alloying with metals, often at concentrations greater than 10 at. % and using non-equilibrium methods. Since switching PCMs between the low-resistance crystalline and high-resistance amorphous states requires a heating cycle, the stability of metal-incorporated GeTe ( Ge 0.5 − x M x Te 0.5) films is also critical to practical implementation of these materials in electronic and optoelectronic devices. In this work, we use both density-functional theory and experimental characterization methods to probe the solubility and critical properties of Ge 0.5 − x M x Te 0.5 films. Using first-principles calculations, we determine the enthalpy of formation for GeTe with 2.08, 4.17, and 6.25 at. % of Cu, Fe, Mn, Mo, and Ti and show trends between the stability of the Ge 0.5 − x M x Te 0.5 systems and the atomic position, composition, and distribution of the metal atoms in the GeTe matrix. Out of all the studied systems, Mo was the only metal to cluster within GeTe. Analysis of the Ge–Te bond lengths and volumes of the Ge 0.5 − x M x Te 0.5 supercells shows that increasing the atomic concentration (2.08, 4.17, 6.25 at. %) of the different metals causes varied distortions of the crystal structure of GeTe that are accompanied by significant changes in the projected density of states. Computational predictions concerning metal solubility and the effect of metal incorporation on critical properties of GeTe are compared to experimental results in the literature (Cu, Mn, Mo, and Ti) and to transmission electron microscopy and transport data from newly characterized co-sputtered Ge 0.5 − x Fe x Te 0.5 films. The computational predictions of decreasing solubility (Mn > Cu, Fe > Ti, Mo) shows good agreement with experimental observations (Mn, Cu > Fe > Ti, Mo), and Ge 0.5 − x Fe x Te 0.5 films exhibited increased crystallization temperatures from pure GeTe.