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Search Results: 1 - 10 of 417 matches for " Prabuddha Sanyal "
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Is Agricultural Production Spillover the Rationale behind CAADP Framework? Spatial Panel Model Approach  [PDF]
John Ulimwengu, Prabuddha Sanyal
Modern Economy (ME) , 2013, DOI: 10.4236/me.2013.45041

The creation of a union is often rationalized on grounds of moving the equilibrium toward the first best solution whenever independent policies generate spillovers. This arises as a common agenda can significantly reduce the scope of free-riding behavior among member countries. In addition, cross-border externalities arising out of higher levels of market integration entails countries to agree on policy coordination. The present study explores the extent and magnitude of agricultural production spillover that might validate the adoption of a common agriculture agenda among African countries. Overall, our results suggest the presence of positive and significant agricultural production spillover. No evidence of beggar-thy-neighbor or negative spillover policies was found; on average, each country received 2.5 percent growth as a result of spillover. Our results also suggest that convergence dynamics is much stronger when spillover is accounted for, which provides a rationale for a common agenda such as CAADP.

Aid Effectiveness and Capacity Development: Implications for Economic Growth in Developing Countries  [PDF]
Prabuddha Sanyal, Suresh C. Babu
Modern Economy (ME) , 2012, DOI: 10.4236/me.2012.35075
Abstract: In this paper, we present a stylized model for understanding the relationship between capacity strengthening and eco-nomic growth in an endogenous growth framework. Endogenous growth theory provides a novel starting point for combining individual, organizational, and enabling environmental issues as part of attaining the capacity-strengthening goal. Our results indicate that although donors can play an important role in aiding countries to develop their existing capacities or to generate new ones, under certain conditions, the potential also exists for uncoordinated and fragmented donor activities to erode country capacities. From the policy exercises, we demonstrate that improving economy-wide learning unambiguously increases the rate of growth of output, technology, capital stock, and capacity. Moreover, a donor’s intervention has the maximum impact on the above variables when the economy’s capacity is relatively low. In contrast, donor intervention can lead to “crowding-out effects” when the economy’s capacity is moderately high. Under such a situation, the economy never reaches a new steady state. Our results not only lend support to diminishing returns to aid but also to an S model of development aid and country capacity relationship.
Antiferromagnetic metal phases in double perovskites having strong antisite defect concentrations
Prabuddha Sanyal
Physics , 2015,
Abstract: Recently an antiferromagnetic metal phase has been proposed in double perovskites materials like Sr$_{2}$FeMoO$_{6}$ (SFMO), when electron doped. This material has been found to change from half-metallic ferromagnet to antiferromagnetic metal (AFM) upon La-overdoping. The original proposition of such an AFM phase was made for clean samples, but the experimental realization of La-overdoped SFMO has been found to contain a substantial fraction of antisite defects. A phase segregation into alternate Fe and Mo rich regions was observed. In this paper we propose a possible scenario in which this type of strong antisite concentration can still result in an antiferromagnetic metal phase, by a novel hopping driven mechanism. Using variational calculations, we find that proliferation of such phase segregated domain regions can also result in the stabilization of an A-type AFM over the G-type AFM based on kinetic energy considerations.
Understanding ferromagnetism in Cr-based 3d-5d double perovskites
Prabuddha Sanyal
Physics , 2012, DOI: 10.1103/PhysRevB.89.115129
Abstract: Ferromagnetism in Cr-based double perovskites is analyzed using effective model as well as simulation approach. Starting from a microscopic model proposed recently for this class of double perovskites, an effective spin-only model is derived in the limit of large exchange coupling at the B-site. Analytic expressions for the resultant exchange coupling is derived in certain limiting cases. The behaviour of this exchange is used to provide a plausible explanation for the enhanced ferromagnetic tendency as also the enigmatic increase in Curie temperature observed in Cr-based DP-s, in the series Sr$_{2}$CrWO$_{6}$,Sr$_{2}$CrReO$_{6}$ to Sr$_{2}$CrOsO$_{6}$. The superexchange between neighbouring B and B' sites is found to play a crucial role both in stabilizing ferromagnetism, especially in the latter two compounds, as well as increasing the T$_{c}$.
A Magnetic Model for the Ordered Double Perovskites
Prabuddha Sanyal,Pinaki Majumdar
Physics , 2008, DOI: 10.1103/PhysRevB.80.054411
Abstract: We construct an effective spin model from the coupled spin-fermion problem appropriate to double perovskites of the form A_2BB'O_6. The magnetic model that emerges is reminiscent of double exchange and we illustrate this `reduction' in detail for the case of perfect B-B' structural order, i.e, no antisite disorder. We estimate the effective exchange between the magnetic B ions in terms of the electronic parameters, study the `classical' magnetic model using Monte Carlo techniques, and compare this approach to a full numerical solution of the spin-fermion problem. The agreement is reasonable, and promises a quick estimate of magnetic properties when coupled with ab initio electronic structure. The scheme generalises to the presence of antisite disorder.
Structural Ordering and Antisite Defect Formation in Double Perovskites
Prabuddha Sanyal,Sabyasachi Tarat,Pinaki Majumdar
Physics , 2008, DOI: 10.1140/epjb/e2008-00327-2
Abstract: We formulate an effective model for B-B' site ordering in double perovskite materials A_2BB'O_6. Even within the simple framework of lattice-gas type models, we are able to address several experimentally observed issues including nonmonotonic dependence of the degree of order on annealing temperature, and the rapid decrease of order upon overdoping with either B or B' species. We also study ordering in the `ternary' compounds A_2BB'_{1-y}B''_yO_6 Although our emphasis is on the double perovskites, our results are easily generalizable to a wide variety of binary and ternary alloys.
Evidence of Kinetic Energy Driven Antiferromagnetism in Double Perovskites : A First-principles Study
Prabuddha Sanyal,Hena Das,T. Saha-Dasgupta
Physics , 2009, DOI: 10.1103/PhysRevB.80.224412
Abstract: Using first principles density functional calculations, together with exact diagonalization of Fe-Mo Hamiltonian constructed in a first principles Wannier function basis, we studied the electronic structure of La doped double perovskite compound Sr$_2$FeMoO$_6$. Our calculation show stabilization of kinetic energy driven antiferromagnetic phase for La rich compounds, in agreement with the results obtained on the basis of previous model calculations.
Signature of an antiferromagnetic metallic ground state in heavily electron doped Sr2FeMoO6
Somnath Jana,Carlo Meneghini,Prabuddha Sanyal,Soumyajit Sarkar,Tanusri Saha-Dasgupta,Olof Karis,Sugata Ray
Physics , 2012, DOI: 10.1103/PhysRevB.86.054433
Abstract: Sr$_{2}$FeMoO$_6$ is a double perovskite compound, known for its high temperature behavior. Combining different magnetic and spectroscopic tools, we show that this compound can be driven to rare example of antiferromagnetic metallic state through heavy electron doping. Considering synthesis of Sr$_{2-x}$La$_x$FeMoO$_6$ (1.0 $\le{x}\le$ 1.5) compounds, we find compelling evidences of antiferromagnetic metallic ground state for $x\ge$1.4. The local structural study on these compounds reveal unusual atomic scale phase distribution in terms of La, Fe and Sr, Mo-rich regions driven by strong La-O covalency: a phenomenon hitherto undisclosed in double perovskites. The general trend of our findings are in agreement with theoretical calculations carried out on realistic structures with the above mentioned local chemical fluctuations, which reconfirms the relevance of the kinetic energy driven magnetic model.
Unusual doping and temperature dependence of photoemission spectra from manganites
Prabuddha Sanyal,Subhra Sen Gupta,Nandan Pakhira,H. R. Krishnamurthy,D. D. Sarma,T. V. Ramakrishnan
Physics , 2007, DOI: 10.1209/0295-5075/82/47010
Abstract: A recent, major, puzzle in the core-level photoemission spectra of doped manganites is the observation of a 1-2 eV wide shoulder with intensity varying with temperature T as the square of the magnetization over a T scale of order 200K, an order of magnitude less than electronic energies. This is addressed and resolved here, by extending a recently proposed two electron fluid l-b model for these systems to include core-hole effects. The shoulder arises from a rapid redistribution of e_g electron density, as a function of T, between the highly localized (l) and band-like (b) states. Furthermore, our theory leads to a correspondence between spectral changes due to increasing doping and decreasing T, as experimentally observed.
Origin of Magnetism and trend in $T_{c}$ in Cr-based double perovskites: Interplay of two driving mechanisms
Hena Das,Prabuddha Sanyal,T. Saha-Dasgupta,D. D. Sarma
Physics , 2011, DOI: 10.1103/PhysRevB.83.104418
Abstract: Employing first principles density functional calculations, together with solution of the low-energy, model Hamiltonian constructed in a first principles manner, we explored the origin of magnetism and $T_c$ trend in Cr-based double perovskite series, Sr$_2$CrB$'$O$_6$ (B$'$=W/Re/Os). Our study shows that the apparently puzzling $T_c$ trend in Sr$_2$CrB$'$O$_6$ (B$'$=W/Re/Os) series can be understood in terms of the interplay of the hybridization driven mechanism and the super-exchange mechanism.
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