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    Item type:Item, Article Access status: Open Access ,
    Characterization of Two Members of the N-(p-n-alkoxy benzylidene)-p-n-alkyl anilines (nO.m) Series Using Complementary Experimental Techniques
    (University of North Bengal, 2026) Sarkar, Prabir; Malay, Kumar Das
    In this study, we present a detailed investigation of the phase behavior of two homologues, namely 5O.12 and 5O.14, belonging to the series N-(p-n-alkoxy benzylidene)-p-n alkyl anilines (nO.m). A combination of high-resolution experimental techniques, including optical transmission, static dielectric permittivity, and modulated differential scanning calorimetry (MDSC), was employed to probe the isotropic–nematic (I–N), nematic–smectic A (N– SmA), and smectic A–smectic B (SmA–SmB) phase transitions. Temperature-dependent birefringence measurements indicate a progressive enhancement of orientational and bondorientational ordering upon cooling. Dielectric studies reveal negative dielectric anisotropy, attributed to the lateral dipole moment associated with the −C(H) = N− linkage within the molecular core. Calorimetric investigations, including heat-capacity anomalies and latentheat evaluation, confirm the first-order character of all observed transitions. Furthermore, critical analysis based on renormalization-group (RG) scaling expressions yields critical exponent values (α) characteristic of weakly first-order behavior. The results highlight the significant role of terminal alkyl chain length in modulating mesomorphic properties and provide deeper insight into the molecular ordering processes governing higher-order smectic phase transitions.
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    Item type:Item, Article Access status: Open Access ,
    On the Ferroelectricity in CaBaCo3.96Ni0.04O7
    (University of North Bengal, 2026) Islam, Mijanul; Karmakar, Arindam
    Studies over the last decade demonstrate a large electric polarization and a substantial ferrimagnetic moment in CaBaCo4O7. The robust polarization, produced along the crystallographic c-direction, is however recently found to be a result of pyroelectricity rather than switchable polarization as in ferroelectricity. A contemporary investigation of lightly Nidoped CaBaCo4O7 derivatives claims switchable polarization indicating ferroelectricity in the materials. In an attempt to delve deeper into the debate, we have attempted direct P(E) loop measurements of two compounds as a comparison–a 1% Cr-doped (trivalent) and a 1% Ni-doped (divalent) CaBaCo4O7 derivative. The Ni-doped compound shows ferroelectriclike P(E) loops while the Cr-doped compound does not. We have also discussed the possible origin of the switchability of the polarization from the perspective of structural distortion and argued that a possible candidate is the buckling of the CoO4 tetrahedra rather than the cooperative orthorhombic distortion which only enhances the net pyroelectric polarization.
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    Item type:Item, Article Access status: Open Access ,
    A First-Principles Study on Electronic, Magnetic and Optical Properties of Two-Dimensional Janus FeSX (X = Se, Te)
    (University of North Bengal, 2026) Sengupta, Amretashis
    In this work, we study with first-principles methods the electronic material properties of two-dimensional (2D) Janus iron dichalcogenides FeSSe and FeSTe. Using density functional theory (DFT) calculations with the generalized gradient approximation (GGA) and the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional, we study 2D Janus structures. Structural optimization shows a P3m1 structure for the said materials characterized by a central iron layer covalently bonded between two distinct chalcogen layers. Both FeSSe and FeSTe exhibit metallic character with complex, multi-band Fermi surfaces dominated by Fe 3d orbitals and van Hove singularities. A significant finding is the presence of spontaneous magnetization and exchange splitting, confirming magnetically ordered ground states. FeSSe displays a ferromagnetic coupling with a total magnetization of 1.96 μB, whereas FeSTe exhibits a quenched magnetic state of 0.47 μB due to ferrimagnetic-like tendencies of the Te atoms. Optical calculations show impressive light-harvesting capabilities, with absorption coefficients 1.5 − 1.8×106 cm−1 in the ultraviolet region (αz peaks around 113−174 nm for FeSSe and 114−158 nm for FeSTe) and a broad response extending into the near-infrared to visible region. Furthermore, the inherent structural asymmetry induces a pronounced out-of-plane charge disparity, resulting in an intrinsic electric dipole moment. These findings suggest that 2D Janus Fe-based materials are promising candidates for valleytronics, spintronic injectors, polarization-sensitive photodetectors, catalysis, and the exploration of emergent quantum phases, such as unconventional superconductivity.
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    Item type:Item, Article Access status: Open Access ,
    Thermodynamic Behaviour of Viscous Variable Chaplygin Gas in a Flat Universe
    (University of North Bengal, 2026) Barman, Purna Chandra; Barman, Abhinath
    In this manuscript we have studied the thermodynamic stability of the viscous variable Chaplygin gas (VVCG) model. The equation of state p = −B ρ is employed, where B = B0V −n 3 and B0 is a positive universal constant. The bulk viscosity coefficient ξ = ξ0ρ 1 2 has also been included in our research. When a fluid satisfies the established stability requirements, we obtain the intriguing conclusion that ( ∂peff ∂V )S < 0 and ( ∂peff ∂V )T < 0 throughout the evolution for ξ0 < 0, when n without a certainty, are limited to the negative values. Additionally, the third law of thermodynamics is assured to be valid in this instance, as is the positivity of thermal heat capacity (cV ). Also we have discussed that how thermal variables depend on either temperature or volume. A new general equation of state for the VVCG model as a function of volume and temperature is obtained during the thermal process, which also shows that the cosmos is thermodynamically stable. Furthermore, the thermal and caloric equation-of-state parameters coincide at large volume in the limit T → 0.
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    Item type:Item, Article Access status: Open Access ,
    Comparative Observational Analysis of Barrow and Tsallis Holographic Dark Energy in Braneworld Models
    (University of North Bengal, 2026) Ghose, Souvik
    We perform a comparative observational analysis of Barrow and Tsallis holographic dark energy models within the framework of braneworld cosmology. Working in the Dvali– Gabadadze–Porrati (DGP) and Randall–Sundrum type II (RSII) scenarios, we consider the Hubble horizon as the infrared cutoff and constrain the models using Observed Hubble Data (OHD). Building upon earlier dynamical studies and a preliminary observational analysis of Barrow holographic dark energy, we employ a Bayesian Markov Chain Monte Carlo approach to obtain marginalized posterior distributions, confidence intervals and parameter correlations. Our results show that the Barrow holographic dark energy model yields wellconstrained deformation parameters in both DGP and RSII braneworlds, consistent with their theoretical bounds and exhibiting weak parameter degeneracies. In contrast, while the Tsallis holographic dark energy provides an acceptable fit to the OHD data, its normalization parameter remains weakly constrained, and the preferred values of the Tsallis exponent differ significantly from those commonly adopted in earlier dynamical analyses. These results indicate that observational constraints favor the Barrow formulation over the Tsallis one within the braneworld context considered here, and thereby highlighting the role of theoretical entropy bounds in improving the robustness of holographic dark energy models.