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P. K. Mukhopadhyay

Bio: P. K. Mukhopadhyay is an academic researcher from S.N. Bose National Centre for Basic Sciences. The author has contributed to research in topics: Magnetization & Magnetic shape-memory alloy. The author has an hindex of 16, co-authored 87 publications receiving 924 citations. Previous affiliations of P. K. Mukhopadhyay include Bose Corporation & Indian Institute of Science.


Papers
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TL;DR: The crystal structure of Ni{sub 2+x}Mn{sub 1-x}Ga has been studied as a function of composition (x) by powder x-ray diffraction.
Abstract: The crystal structure of Ni{sub 2+x}Mn{sub 1-x}Ga has been studied as a function of composition (x) by powder x-ray diffraction. For Ni{sub 2.24}Mn{sub 0.75}Ga, where one-fourth of the Mn atoms are replaced by Ni, the experimentally determined lattice constants are in good agreement with theoretical equilibrium lattice constants calculated by minimization of total energy using full potential linearized augmented plane-wave method. For 0.15{<=}x{<=}0.35, a nonmodulated tetragonal martensitic phase is obtained at room temperature, whose lattice constant c increases and a decreases linearly with increasing x following Vegard's law. A 7M modulated monoclinic phase is obtained for x=0.2 due to annealing. The small width of the hysteresis of the martensitic transition shows its thermoelastic nature that is the characteristic of a shape memory alloy. Phase coexistence is observed for 0.1{<=}x{<=}0.15 at room temperature, confirming the first-order nature of the martensitic transition.

75 citations

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TL;DR: In this paper, the transformation behavior of these two alloys is found to be entirely different, and it is shown that the martensite phase belongs to the Pnnm space group with $7M$ modulation.
Abstract: Results of temperature-dependent magnetic susceptibility and powder x-ray diffraction (XRD) measurements on ${\mathrm{Ni}}_{2}{\mathrm{Mn}}_{105}{\mathrm{Ga}}_{095}$ and ${\mathrm{Ni}}_{213}{\mathrm{Mn}}_{087}\mathrm{Ga}$ magnetic shape memory alloys are compared The transformation behavior of these two alloys is found to be entirely different Detailed LeBail and Rietveld analyses of powder XRD data of ${\mathrm{Ni}}_{2}{\mathrm{Mn}}_{105}{\mathrm{Ga}}_{095}$ alloy show that the martensite phase belongs to the Pnnm space group with $7M$ modulation The limits of the supercooled austenite and the superheated martensite phases have been determined by Rietveld analysis of powder XRD data recorded at close temperature intervals It is shown that the martensite and the austenite phases coexist over $\ensuremath{\sim}30\phantom{\rule{03em}{0ex}}\mathrm{K}$ temperature range around the martensitic transition temperature The transformation strains during cooling in [001], [010], and [100] directions are found to be $\ensuremath{-}4%$, $+16%$, and $21%$, respectively, while the volume change is only 006%

68 citations

Journal ArticleDOI
TL;DR: In this article, the structural, magnetic and transport properties of nanoparticles of Pr0.5Ca 0.5MnO3 (PCMO) were investigated with particle sizes as small as 15nm synthesized by polyol route.
Abstract: In this paper we report the structural, magnetic, and transport properties of nanoparticles of Pr0.5Ca0.5MnO3(PCMO). On comparing our results with that of bulk PCMO, we find that there is a likely destabilization of charge ordering in nanoparticles of PCMO. The investigation has been done with particle sizes as small as 15nm synthesized by polyol route. The size reduction (by keeping the chemical composition unchanged) reduces the orthorhombic c axis preferentially and thus reduces the orthorhombic distortion. The size reduction to 15nm enhances the ferromagnetic moment at low temperatures and strongly suppresses the activated charge transport which is seen in the bulk samples of charge ordered PCMO.

49 citations

Journal ArticleDOI
TL;DR: A negative-positive-negative switching behavior of magnetoresistance (MR) with temperature is observed in a ferromagnetic shape memory alloy as mentioned in this paper, which is related to a magnetic transition.
Abstract: A negative-positive-negative switching behavior of magnetoresistance (MR) with temperature is observed in a ferromagnetic shape memory alloy ${\text{Ni}}_{1.75}{\text{Mn}}_{1.25}\text{Ga}$. In the austenitic phase between 300 and 120 K, MR is negative due to $s\text{\ensuremath{-}}d$ scattering. Curiously, below 120 K MR is positive, while at still lower temperatures in the martensitic phase, MR is negative again. The positive MR cannot be explained by Lorentz contribution and is related to a magnetic transition. Evidence for this is obtained from ab initio density-functional theory, a decrease in magnetization and resistivity upturn at 120 K. Theory shows that a ferrimagnetic state with antiferromagnetic alignment between the local magnetic moments of the Mn atoms is the energetically favored ground state. In the martensitic phase, there are two competing factors that govern the MR behavior: a dominant negative trend up to the saturation field due to the decrease in electron scattering at twin and domain boundaries and a weaker positive trend due to the ferrimagnetic nature of the magnetic state. MR exhibits a hysteresis between heating and cooling that is related to the first-order nature of the martensitic phase transition.

43 citations

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TL;DR: In this paper, the authors determined the phase diagram of Ni2+xMn1�xGa as a function of x 0x 0.35 from ac susceptibility and differential scanning calorimetry DSC using the ab initio full potential linearized plane-wave FPLAPW method.
Abstract: We determine the phase diagram of Ni2+xMn1�xGa as a function of x 0x 0.35 from ac susceptibility and differential scanning calorimetry DSC. Total energy and density of states calculated using the ab initio full potential linearized plane-wave FPLAPW method explain the phase diagram. A martensitic paramagnetic phase for x 0.2 has been identified. The structure of this phase is found to be tetragonal from hightemperature x-ray-diffraction XRD studies. XRD, magnetization, and DSC measurements show that the paramagnetic tetragonal phase evolves from the lower temperature ferromagnetic tetragonal phase through a second-order phase transition without any change of structure. The unoccupied conduction band has been studied by inverse photoemission spectroscopy. It is dominated by Mn 3d-like states, and is in good agreement with FPLAPW based calculations.

41 citations


Cited by
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TL;DR: The phenomenology of exchange bias and related effects in nanostructures is reviewed in this paper, where the main applications of exchange biased nanostructure are summarized and the implications of the nanometer dimensions on some of the existing exchange bias theories are briefly discussed.

1,721 citations

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TL;DR: The magnetocaloric effect and its most straightforward application, magnetic refrigeration, are topics of current interest due to the potential improvement of energy efficiency of cooling and temperature control systems, in combination with other environmental benefits associated to a technology that does not rely on the compression/expansion of harmful gases.

941 citations

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TL;DR: The magnetocaloric effects of Ni-Mn-based Heusler alloys are surveyed and their relation with the magnetic shape-memory and magnetic superelasticity reported in these materials are discussed.
Abstract: Magnetic Heusler alloys which undergo a martensitic transition display interesting functional properties. In the present review, we survey the magnetocaloric effects of Ni-Mn-based Heusler alloys and discuss their relation with the magnetic shape-memory and magnetic superelasticity reported in these materials. We show that all these effects are a consequence of a strong coupling between structure and magnetism which enables a magnetic field to rearrange martensitic variants as well as to provide the possibility to induce the martensitic transition. These two features are respectively controlled by the magnetic anisotropy of the martensitic phase and by the difference in magnetic moments between the structural phases. The relevance of each of these contributions to the magnetocaloric properties is analysed.

886 citations

Journal Article
TL;DR: In the limit of a QD much smaller than the bulk exciton size, the linear spectrum will be a series of lines, and the phonon broadening of these lines is considered.
Abstract: We analyze theoretically the optical properties of ideal semiconductor crystallites so small that they show quantum confinement in all three dimensions [quantum dots (QD's)]. In the limit of a QD much smaller than the bulk exciton size, the linear spectrum will be a series of lines, and we consider the phonon broadening of these lines. The lowest interband transition will saturate like a two-level system, without exchange and Coulomb screening. Depending on the broadening, the absorption and the changes in absorption and refractive index resulting from saturation can become very large, and the local-field effects can become so strong as to give optical bistability without external feedback. The small QD limit is more readily achieved with narrow-band-gap semiconductors.

788 citations

Journal ArticleDOI
TL;DR: Evidence is provided that IO/PVA nanoparticles inhibited S. aureus growth at the highest concentration (3 mg/mL) at all time points.
Abstract: In order to study the effects of iron oxide (IO) nanoparticles on Staphylococcus aureus, IO nanoparticles were synthesized via a novel matrix-mediated method using polyvinyl alcohol (PVA). The IO nanoparticles were characterized by transmission electron microscopy and dynamic light scattering. Further, S. aureus were grown in the presence of three different IO nanoparticle concentrations for four, 12, and 24 hours. Live/dead assays were performed and the results provide evidence that IO/PVA nanoparticles inhibited S. aureus growth at the highest concentration (3 mg/mL) at all time points.

347 citations