Browsing by Author "Adyam, V."

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Low field-cooled induced large exchange bias effect and DFT calculations in ferromagnetic Sm2CoMnO6
(Elsevier Ltd, 2024) Nayak, A.; Prashanth, C.H.; Bala, D.; Reddy, I.R.; Tarafder, K.; Adyam, V.; Jyothinagaram, K.
In the present report, we study the large exchange bias effect in Sm2CoMnO6 (SCMO) polycrystalline samples synthesized with the presence of two crystallographic phases: ordered-phase (monoclinic; P21/n) and disordered-phase (orthorhombic; Pnma). X-ray photoelectron spectroscopy study revealed the presence of mixed valence states for Co (2+ & 3+) and Mn (4+ & 3+). M(T) data exhibits an inhomogeneous magnetic state with the presence of ferromagnetic ordering at TC ∼128 K due to the super-exchange interactions of Co2+-O2--Mn4+ and antiferromagnetic-like spin correlations for T < 50 K, attributed to Co3+-O2--Co3+, and Mn3+-O2--Mn3+ interactions. M(H) loop shift with a conventional exchange bias (EB) effect of 10 kOe for a field-cooled (HFC) of 10 kOe at 2 K was observed. Such a large value of the EB effect for low HFC in SCMO is comparable to that of large EB compounds, such as La1·5Sr0·5CoMnO6 and NiFe2O4/CoO nanocomposites. The zero-field cooled asymmetry in the M(H) loop is termed a spontaneous exchange bias effect (SEB) observed for T < 20 K. The systematic study of EB effects like HEB and MEB with T(K) and HFC was explained qualitatively by the presence of unidirectional anisotropy formed at the interface of inhomogeneous magnetic phases. Further, density functional theory (DFT) calculations validate the ferromagnetic ground state of SCMO with Co and Mn networks. Moreover, the semiconductor characteristics of SCMO are established with a band gap of 1.3 eV. © 2023
Magnetic complexity, magnetodielectric effect and DFT calculations on correlation driven Gd2CoMnO6 insulator
(Elsevier B.V., 2022) Prashanth, C.H.; Reddy, I.; Tarafder, K.; Chandrasekhar Kakarla, D.; Yang, H.D.; Adyam, V.; Jyothinagaram, K.
In the family of Re2CoMnO6 manganite double perovskites, in contrast to parent La2CoMnO6 compound, Gd2CoMnO6 exhibits multiple magnetic transitions; ferromagnetic (FM) ordering, TC ∼ 112 K followed by AFM transition, TN ∼ 47 K, Gd spins ordering for T < 10 K and large isothermal entropy changes. A study of DC field-superimposed AC magnetic susceptibility measurements revealed the field-induced magnetic glassy behavior below TC and enhancement of FM correlations above TC. From the analysis of Almeida-Thouless behavior and dynamical power-law fit to frequency dependent AC susceptibility, Gd2CoMnO6 exhibits a volume spin glass-like nature below the freezing temperature, Tf ∼ 117.5 K. The isothermal field-dependent magnetic and dielectric permittivity data and temperature dependent Raman measurements (reported in ref. R. X. Silva et al., J, Appl. Phys. 114 194,102 (2013)) confirms the spin-phonon coupling induced magnetodielectric effect. Further, the ground-state electronic structure and magnetic properties of Gd2CoMnO6 are investigated using DFT + U formalism with Vienna Ab-initio Simulation Package (VASP) code and predicted the material to be a correlation-driven insulator. The correlation value of the Hubbard U parameter at the 4f-Gd elements changes the stability of the magnetic state from Ferri to FM spin alignment for Ueff ≥ 3 eV and is correlated to the experimentally observed field-induced transformation of the short-range-order FiM/spin-glass-like phase into the long-range ordered FM phase. © 2022
Polymer Electrolytes and Separators for Magnesium-Ion Batteries
(CRC Press, 2024) Singh, R.; Khalifa, M.; Janakiraman, S.; Adyam, V.; Anandhan, S.; Biswas, K.
Magnesium (Mg)-ion-based rechargeable batteries are attractive because magnesium is bivalent, abundant, non-toxic, and inexpensive. In the development of Mg-ion batteries (MIBs) with high energy densities, their ionic conductivity and safety have become important features. The most commonly used cathodes are Mo6S8, MoO3, V2O5, MnO2, and TiO2, but they are limited due to low voltages (<2.0 V) and low specific capacities. Therefore, electrolytes are needed to improve the voltage stability and ease of synthesis. In this chapter, polymer electrolytes and separators in MIBs with liquid or gel electrolytes are briefly outlined. Polymer electrolytes are classified into two categories, namely solid polymer electrolytes and gel polymer electrolytes (GPEs). Solid polymer electrolytes have several advantages such as high safety, lightweight, and favorable mechanical properties, but their weakness is their relatively lower ionic conductivity. To overcome these issues, GPE, which is a combination of liquid electrolyte and a polymer matrix, is explored. Poly(vinylidene fluoride)-based gel electrolytes showed a high ionic conductivity of the order of 10−3 S cm−1 at room temperature. In GPEs, an electrolyte is used as an ion transport medium between the electrodes, whereas a polymer membrane acts as a separator, thereby eliminating the physical contact between the electrodes. © 2025 selection and editorial matter, Prasanth Raghavan, Akhila Das, and Jabeen Fatima M. J.
Synthesis and evaluation of a new gel polymer electrolyte for high-performance Li-ion batteries from electrospun nanocomposite of PVDF/Ca–Al-layered double hydroxide
(Springer Nature, 2022) Shamitha, C.; Janakiraman, S.; Ghosh, S.; Adyam, V.; Prabhu, K.N.; Anandhan, S.
Poly(vinylidene fluoride) (PVDF)/Ca–Al-layered double hydroxide(CAL) (PCL) nanocomposite-based nanofabrics were electrospun for application in lithium-ion batteries as gel polymer electrolyte (GPE). The nanofabric exhibited a high β-phase content of 82.79% after the addition of CAL that was synthesized by co-precipitation method. The PCL-based GPE exhibited enhanced electrochemical properties, such as high ionic conductivity, optimal Li-ion transference number, and improved electrolyte uptake due to the presence of a highly interconnected porous structure. The PCL GPE exhibited an ionic conductivity of 3.54 × 10–3 S cm−1 at ambient temperature, which is much higher than that of pristine PVDF and commercial Celgard® 2400 separators. Moreover, Li/PCL/LiCoO2 cell showed an initial discharge capacity of 140.31 mAh g−1, which is superior to that of PVDF and Celgard® 2400 separators. It also exhibited high coulombic efficiency retention of 99% after 30 cycles of charging. PCL-based GPE showed superior mechanical and low thermal shrinkage properties, indicating its suitability in battery separator application. Graphical abstract: [Figure not available: see fulltext.] © 2022, The Author(s), under exclusive licence to The Materials Research Society.