arXiv subjects

Rudra Banerjee

Publications and source records attributed to Rudra Banerjee.

15 recordsLinked to original sources

arXiv2026

d-band filling dictates magnetic stability in Mn- and Co-substituted FeRh alloys

The composition-dependent magnetic properties of B2-ordered \zfr~alloys with substitutional disorder on the Fe sublattice are investigated using first-principles calculations within the coherent potential approximation. By systematically substituting Mn and Co on the Fe sublattice, we establish $d$-band filling as the primary control parameter governing magnetic stability in this itinerant system. Mn substitution (hole doping) shifts the Fermi level into the minority-spin bonding states, driving a collapse of spin polarization (crossing zero at $x \approx 0.5$) and the emergence of competing antiferromagnetic interactions ($\eta_\mathrm{Mn} < 0$). Even though the ferromagnetic configuration remains energetically well separated from the G-type AFM-II configuration across the studied range ($\Delta E$ up to $\sim$0.35~eV/atom), this exchange competition drives an ``itinerant magnetic softness'' that suppresses the Curie temperature by $\sim$450~K -- a finite-temperature instability set by the near-cancellation of competing exchange interactions rather than by AFM--FM energy proximity. In contrast, Co substitution (electron doping) acts as a ``magnetic hardener'' by pinning the Fermi level within the majority-spin pseudogap, preserving high spin polarization ($|P| \approx 0.75$) and stabilizing ferromagnetic exchange across the full composition range. These results show that tuning the Fermi level relative to the pseudogap provides a systematic, microscopic framework for controlling magnetic stability in B2-ordered itinerant magnets, distinct from simple magneto-volume models.

cond-mat.mtrl-sci↗

arXiv2026

Hyperfine Structure and Exchange Coupling of Vacancy-Induced Ce$^{3+}$ Spin Centers in Nuclear-Spin-Dilute CeO$_2$

Oxygen vacancies in ceria CeO$_2$ donate electrons that localize as Ce$^{3+}$ ($4f^1$, $S=1/2$) small polarons, creating rare-earth spin centers through native defect chemistry rather than implantation or extrinsic doping. We investigate the magnetic environment of these centers using first-principles PBE$+U$ calculations with a linear-response Hubbard parameter ($U=5.8382$ eV), hyperfine tensors from the all-electron reconstruction of the projector-augmented-wave method, and Korringa-Kohn-Rostoker exchange calculations within the coherent-potential approximation. Four vacancy configurations spanning concentrations from $3.125\%$ to $12.5\%$ are considered. A distinctive feature of the host follows from cerium isotopics: all naturally occurring cerium isotopes possess nuclear spin $I=0$, eliminating on-site hyperfine interactions at the Ce$^{3+}$ center and leaving the nuclear-spin bath entirely on the oxygen sublattice, whose sole magnetic isotope, $^{17}O$ ($I=5/2$), occurs at $0.038\%$ natural abundance. The resulting $^{17}O$ hyperfine landscape consists of a small number of strongly coupled, nearly axial first-shell nuclei with contact couplings reaching $6$~MHz, surrounded by a weakly coupled and strongly anisotropic outer shell. These tensors define experimentally accessible signatures for $^{17}O$ ESEEM and HYSCORE measurements and provide the microscopic hyperfine parameters required for cluster-correlation-expansion calculations of spin coherence. Exchange interactions between neighboring polarons are weak and oxygen-mediated, leaving the vacancy-generated spins largely independent over the concentration range considered. Together, these results establish oxygen-deficient CeO$_2$ as a chemically generated and intrinsically nuclear-spin-dilute host for rare-earth spin centers, and provide the first-principles magnetic parameters needed to assess their coherence properties.

cond-mat.mtrl-sci↗

arXiv2026

Auditing Machine-Learning Models and Their Training Data with Explainability and First-Principles Verification: Application to Spin Hall Conductivity

Machine-learning models for materials properties rest on two assumptions that standard validation never tests: that a model's features reflect the physics of the property rather than accidents of the training distribution, and that the training labels are themselves correct. We introduce a model-agnostic audit protocol for both, combining SHAP attribution, counterfactual partial dependence analysis, and Rashomon-style cross-model verification, with every finding adjudicated by targeted density functional theory (DFT). Demonstrated on intrinsic spin Hall conductivity using a composition-only Random Forest, the model needs no relaxed crystal structure, reaching accuracy competitive with structure-aware graph networks while remaining applicable to the far larger space of compositions for which no structure has been computed. The model audit reveals that the average p-valence descriptor becomes statistically entangled with Pt content - a property of the learned representation rather than the physics; DFT confirms the consequence, a Pt-free compound (HgOsPb$_2$) whose true SHC is nearly four times the prediction. The data audit exposes a thirtyfold error in the HfC training label, inherited undetectably by every black-box model trained on the same data. The protocol audits a model and its training data for the cost of a few DFT calculations, wherever one element dominates the high-property regime.

cond-mat.mtrl-sci↗

arXiv2026

Geometric Percolation Threshold Defines Half-Metallic Window in Vacancy-Doped Titanium disulfides

Defect engineering of two-dimensional materials routinely produces local magnetic moments, yet itinerant half-metallic ferromagnetism remains elusive -- experiments frequently yield paramagnetic insulators. We resolve this paradox for vacancy-doped monolayer $1T$-\ptis~by demonstrating that the insulator-to-half-metal transition is governed by universal geometric percolation of the defect network, extending the percolation framework established for three-dimensional diluted magnetic semiconductors into the 2D vacancy-doped regime. Half-metallicity emerges via a two-step mechanism: crystal-field symmetry breaking ($O_h \to C_{4v}$) selectively stabilizes the Ti $3d_{z^2}$ orbital, generating robust local moments ($0.94~\mu_B$), but spin-polarized transport requires these moments to form a spanning cluster. At critical vacancy concentration $x_c \approx 12.5\%$, a percolation transition drives the majority-spin impurity band from flat, localized levels ($W < 0.1$~eV) to a dispersive 1.5~eV-wide band with 100\% spin polarization and a minority-spin gap of 1.0~eV. The percolation mechanism is independently corroborated by a striking supercell-size effect: at identical concentration, $2\times2$ cells yield antiferromagnetic order while $4\times4$ cells mandate ferromagnetism, reflecting the presence or absence of a spanning cluster. We estimate a Curie temperature exceeding 300~K from the exchange coupling, and identify a geometric jamming instability at $x > 20\%$ that fragments the network. These results define a narrow functional window ($11\% < x < 15\%$) for half-metallic operation and establish geometric connectivity as a quantitative design principle for defect-engineered 2D spintronics.

cond-mat.mtrl-sci↗

arXiv2025

Beyond Diamond: Interpretable Machine Learning Reveals Design Principles for Quantum Defect Host Materials

Solid-state spin defects in wide-bandgap semiconductors are leading candidates for quantum information processing, but systematic identification of suitable host materials remains limited by the cost of first-principles screening across vast chemical spaces. We address this with a composition-only machine learning framework built on heterogeneous Rashomon set ensembles: by contrasting the feature attributions of seven diverse classifiers, we extract consensus design rules that no single model identifies alone-filled valence s-, d-, and f-shells, low chemical heterogeneity, and enrichment in C, S, Si, and O favor quantum compatibility. Screening approximately 45,000 thermodynamically stable compounds, we identify 122 high-confidence candidates (confidence > 0.95), recovering most experimentally verified hosts (C, SiC, ZnO, ZnS) and predicting unexplored materials including TiO$_2$, PbWO$_4$, and layered chalcogenides (HfS$_2$, ZrS$_2$). Density functional perturbation theory calculations on 12 representative materials validate dielectric screening as a coherence proxy (R$^2$ = 0.89 against experimental T$_2$), and vacancy calculations for TiO$_2$ reveal deep, isolated mid-gap states favorable for spin-defect hosting. The framework provides transferable, physically grounded design principles for rational quantum materials discovery beyond traditional carbide and nitride hosts.

cond-mat.mtrl-sci↗

arXiv2025

Tuning Catalytic Efficiency: Thermodynamic Optimization of Zr-Doped \ce{Ti3C2} and \ce{Ti3CN} MXenes for HER Catalysis

Hydrogen production via the Hydrogen Evolution Reaction (HER) is critical for sustainable energy solutions, yet the reliance on expensive platinum (Pt) catalysts limits scalability. Zirconium-doped (\ce{Zr}-doped) MXenes, such as \ce{Ti3C2} and \ce{Ti3CN}, emerge as transformative alternatives, combining abundance, tunable electronic properties, and high catalytic potential. Using first-principles density functional theory (DFT), we show that \ce{Zr} doping at 3\% and 7\% significantly enhances HER activity by reducing the work function to the optimal range of 3.5-4.5~eV and achieving near-zero Gibbs free energy (\dgh) values of 0.18-0.16~eV, conditions ideal for efficient hydrogen adsorption and desorption. Bader charge analysis reveals substantial charge redistribution with enhanced electron accumulation at \ce{Zr} and \ce{N} sites, further driving catalytic performance. This synergy between optimized electronic structure and catalytic properties establishes \ce{Zr}-doped MXenes as cost-effective, high-performance alternatives to noble metals for HER. By combining exceptional catalytic efficiency with scalability, our work positions \ce{Zr}-doped MXenes as a breakthrough for green hydrogen production, offering a robust pathway toward renewable energy technologies and advancing the design of next-generation non-precious metal catalysts.

cond-mat.mtrl-sci↗

arXiv2023

A Study of Electronic and Magnetic Properties of Transition Metal Trihalides

We present the electronic and magnetic structure calculations of VCl3, VBr3, CrCl3 and CrBr3. The results are obtained by density functional theory with plane wave basis sets. The trihalides generally optimize either in trigonal or monoclinic structures. We have focused on the effect of symmetry on the electronic and magnetic properties of the systems. We have found that magnetic moments change considerably depending on the symmetry. Both CrX3 have shown a bandgap around 2eV while the V-based systems have shown half-metallic properties.

cond-mat.mtrl-sci↗

arXiv2023

Influence of Co and Mn on Electronic and Magnetic properties of Ni2MnGa Heusler alloy

The ferromagnetic Heusler alloy $Ni_2MnGa$ had been of major interest in the past few years because of its magnetic properties which can be easily tuned. The $Ni_2MnGa$ Heusler alloys are intermetallic alloy with $L2_1$ structure. Here we report a detailed investigation of the effect of doping of Co and Mn in Ni2MnGa. Magnetic properties and electronic structure of $Ni_{2-x}Co_xMnGa_{1-y}Mn_y$ Heusler alloys have been studied by using Green's function-based KKR-CPA method based DFT calculations. We will show the magnetization can be tuned depending on the Co and Mn occumencies. We will also discuss the critical temperature, magnetic interactions and magnetic stability of the systems.

cond-mat.mtrl-sci↗

arXiv2022

Tuning electronic and magnetic properties of FeRh alloy by chemical and physical method

The electronic, magnetic, and thermodynamic properties of ordered and chemically disordered FeRh alloy is studied using ab-initio methods. The equiatomic Fe$_{50}$Rh$_{50}$ composition is reported for both ordered and disordered phases. Chemically disordered Fe$_x$Rh$_{100-x}$ is reported and the effect of disorder on electronic and magnetic properties is discussed. Further, We have reported the effects of stress and strain in both the order and disorder phases. The result is only for the cubic phase and no distortion has been taken into consideration. This study is motivated by the recent resurgence in FeRh study motivated by the fact that the barocaloric properties can be possible to sustain over the cycle. Hence, we have discussed the properties of Fe$_x$ Rh${100-x}$ with chemical disorder and pressure together, to gain an insight into the compound effect and the interplay between them

cond-mat.mtrl-sci↗

arXiv2021

Submitting Jobs on Grid

This is an user's introduction to grid using Globus Toolkit from an user's point of view. With a brief introduction to what grid is, I have shifted quickly to the game itself. In this part, i have done an step by step introduction, starting from the access to the grid to submitting the job. In the appendix, a special note is there on using GARUDA grid. Hope this will be of help for the users.

physics.comp-ph↗

arXiv2019

Enhanced Gilbert Damping in Re doped FeCo Films: A Combined Experimental and Theoretical Study

The effects of rhenium doping in the range 0 to 10 atomic percent on the static and dynamic magnetic properties of Fe65Co35 thin films have been studied experimentally as well as with first principles electronic structure calculations focusing on the change of the saturation magnetization and the Gilbert damping parameter. Both experimental and theoretical results show that the saturation magnetization decreases with increasing Re doping level, while at the same time Gilbert damping parameter increases. The experimental low temperature saturation magnetic induction exhibits a 29 percent decrease, from 2.31 T to 1.64 T, in the investigated doping concentration range, which is more than predicted by the theoretical calculations. The room temperature value of the damping parameter obtained from ferromagnetic resonance measurements, correcting for extrinsic contributions to the damping, is for the undoped sample 0.0027, which is close to the theoretically calculated Gilbert damping parameter. With 10 atomic percent Re doping, the damping parameter increases to 0.0090, which is in good agreement with the theoretical value of 0.0073. The increase in damping parameter with Re doping is explained by the increase in density of states at Fermi level, mostly contributed by the spin-up channel of Re. Moreover, both experimental and theoretical values for the damping parameter are observed to be weakly decreasing with decreasing temperature.

cond-mat.mtrl-sci↗

arXiv2014

Ab initio Disordered Local Moment Approach for a Doped Rare-Earth Magnet

Following the finite-temperature ab initio calculation framework based on the relativistic disordered local moments, we computationally demonstrate the possibility of doping-enhanced coercivity at high-temperatures, taking YCo$_5$ as a working material in order to extract the $3d$-electron part of the electronic structure of the rare-earth permanent magnets. Alkaline-earth dopants are shown to be the candidates to realize the proposed phenomenon.

cond-mat.mtrl-sci↗

arXiv2014

Improvement of magnetic hardness at finite temperatures: ab initio disordered local moment approach for YCo$_5$

Temperature dependence of the magnetocrystalline anisotropy energy and magnetization of the prototypical rare-earth magnet YCo$_5$ is calculated from first principles, utilizing the relativistic disordered local moment approach. We discuss a strategy to enhance the finite-temperature anisotropy field by hole doping, paving the way for an improvement of the coercivity near room temperature or higher.

cond-mat.mtrl-sci↗

arXiv2009

Augmented space recursion code and application in simple binary metallic alloy

We present here an optimized and parallelized version of the {\sl augmented space recursion code} for the calculation of the electronic and magnetic properties of bulk disordered alloys, surfaces and interfaces, either flat, corrugated or rough, and random networks. Applications have been made to bulk disordered alloys to benchmark our code.

cond-mat.mtrl-sci↗

arXiv2008

Study of phase stability of MnCr using the augmented space recursion based orbital peeling technique

In an earlier communication we have developed a recursion based approach to the study of phase stability and transition of binary alloys. We had combined the recursion method introduced by Haydock, Heine and Kelly and the our augmented space approach with the orbital peeling technique proposed by Burke to determine the small energy differences involved in the discussion of phase stability. We extend that methodology for the study of MnCr alloys.

cond-mat.mtrl-sci↗