arXiv subjects

Soumyajit Sarkar

Publications and source records attributed to Soumyajit Sarkar.

7 recordsLinked to original sources

arXiv2026

Computational Frameworks for Patterned Two-Dimensional Magnetism

Patterned two-dimensional (2D) magnetic nanostructures constitute geometry-engineered spin systems in which exchange, anisotropy, dipolar coupling, and finite-size effects operate on comparable energy scales. Spatial modulation of continuous magnetic films produces confinement-driven critical behavior, compensation phenomena, metastable switching pathways, and topologically nontrivial textures such as vortices and skyrmions. Computational modeling plays a central role in resolving this complexity, enabling quantitative construction of thermodynamic phase diagrams and analysis of geometry-dependent stability regimes. This review synthesizes theoretical and numerical frameworks for patterned 2D magnetism, including classical spin models, stochastic spin dynamics, rare-event methods, and multiscale parameterization informed by first-principles calculations. Representative systems-nanodot and antidot arrays, artificial spin-ice lattices, exchange-modulated heterostructures, and patterned van der Waals magnets - illustrate how geometry functions as an effective thermodynamic control parameter. Emerging directions in nonequilibrium modeling, multiphysics coupling, and scalable data-centric workflows are discussed in the context of predictive phase mapping. Patterned 2D magnetism thus exemplifies geometry as an effective thermodynamic variable in materials engineering and computational statistical physics, with phase stability and controlled spin textures at the core of next-generation spintronic architectures.

cond-mat.mtrl-sci↗

arXiv2026

Stacking-dependent magnetic ordering in bilayer ScI$_{2}$

Stacking-dependent magnetism in two-dimensional van der Waals materials offers an effective route for controlling magnetic order without chemical modification. Here, we present a combined first-principles and finite-temperature study of magnetic ordering in bilayer ScI$_2$ with different stacking configurations. Using density functional theory with Hubbard-$U$ corrections, we investigate the structural, electronic, and magnetic properties of monolayer and bilayer ScI$_2$ in AA, AB, and BA stackings. The electronic structure exhibits a spin-polarized ground state dominated by Sc-$d$ states near the Fermi level. Mapping total energies onto an effective Heisenberg spin Hamiltonian reveals strong intralayer ferromagnetic exchange that is largely insensitive to stacking, while the interlayer exchange depends strongly on stacking geometry, favoring ferromagnetic coupling for AA and BA stackings and antiferromagnetic coupling for the AB stacking. Spin--orbit coupling calculations show that both monolayer and bilayer ScI$_2$ possess a robust out-of-plane magnetic easy axis. Finite-temperature Monte Carlo simulations indicate that all bilayer configurations sustain magnetic ordering at and above room temperature, with ordering temperatures in the range 360--375$~$K, as confirmed by Binder cumulant analysis and finite-size scaling. These results demonstrate that stacking geometry enables control of the magnetic ground state in bilayer ScI$_2$ without significantly affecting its thermal stability.

cond-mat.mtrl-sci↗

arXiv2026

Multiscale computational approaches to magnetic behaviour in Cobalt Ferrite (CoFe$_2$O$_4$) nanostructures

Cobalt ferrite (CoFe$_2$O$_4$) is a prototypical ferrimagnetic spinel oxide whose exceptional magnetic anisotropy, magnetoelastic coupling, and thermal stability underpin applications in spintronics, magnetic hyperthermia, energy harvesting, and catalysis. This chapter presents a comprehensive computational framework that integrates electronic$-$structure calculations with atomistic spin modeling, statistical mechanics, and continuum micromagnetics to predict magnetic functionality across length and time scales. Starting from density functional theory with Hubbard corrections (DFT$+$U), we derive exchange constants J$_{ij}$, magnetocrystalline anisotropy K$_1$, and magnetoelastic coefficients B$_1$, accounting for cation inversion, strain, and correlation effects. These parameters feed into generalized Heisenberg Hamiltonians, enabling Monte Carlo and Landau-Lifshitz-Gilbert simulations of finite-size effects, hysteresis, coercivity, and hyperthermia response in nanoparticles and thin films. Coarse-graining strategies bridge to micromagnetic modeling, ensuring consistent parameter flow without empirical fitting. Computational case studies demonstrate size-dependent anisotropy enhancement, surface spin disorder, strain-tunable switching, and doping trends, revealing design principles inaccessible to experiment alone. Validation against benchmarks, e.g. Curie temperature, anisotropy constants, coercivity, magnetostriction, confirms predictive accuracy. Current challenges, e.g., U$-$parameter sensitivity, realistic surface chemistry, spin-lattice coupling, and large-scale integration are discussed alongside emerging directions including DFT$+$DMFT, coupled dynamics, and machine-learned potentials.

cond-mat.mtrl-sci↗

arXiv2024

Tunable dynamical tissue phantom for laser speckle imaging

We introduce a novel method to design and implement a tunable dynamical tissue phantom for laser speckle-based in-vivo blood flow imaging. This approach relies on Stochastic Differential Equations (SDE) to control a piezoelectric actuator which, upon illuminated with a laser source, generates speckles of pre-defined probability density function and auto-correlation. The validation experiments show that the phantom can generate dynamic speckles that closely replicate both surfaces as well as deep tissue blood flow for a reasonably wide range and accuracy.

physics.med-ph↗

arXiv2020

Electronic correlation, magnetic structure and magnetotransport in few-layer CrI3

Using density functional theory combined with a Hubbard model (DFT+U ), the electronic band structure of CrI3 multilayers, both free-standing and enclosed between graphene contacts, is calculated. We show that the DFT+U approach, together with the 'around mean field' correction scheme, is able to describe the vertical magnetotransport in line with the experimental measurements of magnetoresistance in multi-layered CrI3 enclosed between graphene contacts. Moreover, by interpolating between different double-counting correction schemes, namely the 'around mean field' correction and the fully localized limit, we show their importance for describing both the band structure and the ground-state total energy consistently. Our description of the magnetic exchange interaction is compatible with the experimentally observed antiferromagnetic ground state in the bilayer CrI3 and the transition to a ferromagnetic arrangement in a small external magnetic field. Thus, using spin-polarized DFT+U with an 'around mean field' correction, a consistent overall picture is achieved.

cond-mat.mtrl-sci↗

arXiv2015

Probing the Orbital Origin of Conductance Oscillations in Atomic Chains

We investigate periodical oscillations in the conductance of suspended Au and Pt atomic chains during elongation under mechanical stress. Analysis of conductance and shot noise measurements reveals that the oscillations are mainly related to variations in a specific conduction channel as the chain undergoes transitions between zigzag and linear atomic configurations. The calculated local electronic structure shows that the oscillations originate from varying degrees of hybridization between the atomic orbitals along the chain as a function of the zigzag angle. These variations are highly dependent on the directionality and symmetry of the relevant orbitals, in agreement with the order-of-magnitude difference between the Pt and Au oscillation amplitudes observed in experiment. Our results demonstrate that the sensitivity of conductance to structural variations can be controlled by designing atomic-scale conductors in view of the directional interactions between atomic orbitals.

cond-mat.mes-hall↗

arXiv2012

Signature of an antiferromagnetic metallic ground state in heavily electron doped Sr2FeMoO6

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.

cond-mat.mtrl-sci↗