arXiv subjects

Arti Kashyap

Publications and source records attributed to Arti Kashyap.

11 recordsLinked to original sources

arXiv2026

Effects of Interfacial States and Strain on Tunnel Magnetoresistance in van der Waals Magnetic Tunnel Junctions

All-two-dimensional magnetic tunnel junctions promise atomically sharp interfaces, yet the role of interface-induced states in their spin transport is not fully understood. Here, we theoretically investigate spin-dependent transport in van der Waals magnetic tunnel junctions of the structure Cr$_2$C/$MY_2$/Cr$_2$C ($M$ = Mo, W; $Y$ = S, Se) with barrier thicknesses of 3, 5, 7, and 9 layers. The broad features of the $\mathbf{k}_{\parallel}$-resolved conductances, namely suppression near the $Γ$ point and enhancement at six off-$Γ$ hot spots, are consistent with the decay of evanescent states in the barrier. However, trilayer WS$_2$, MoSe$_2$, and WSe$_2$ barriers exhibit conductances of the order of $e^2/h$ at $\mathbf{k}_{\parallel}$ points within the hot spots. We attribute these near-unity transmission channels to resonant coupling between the interfacial states at the two electrode--barrier interfaces, as evidenced by their weak but finite residual weight at the barrier center. For thicker barriers, this coupling weakens, which suppresses the residual weight, thereby reducing the tunnel magnetoresistance (TMR) ratio of the MoS$_2$ junction while enhancing those of the other junctions. To exploit the interfacial states for spin-selective tunneling, we further examine biaxial tensile strain applied to the trilayer junctions. At 4\% strain, the TMR ratio increases from 176\% to 540\% for MoS$_2$ and from 98\% to 496\% for WS$_2$, whereas MoSe$_2$ and WSe$_2$ exhibit comparatively weaker enhancement. Our results establish interfacial-state engineering via strain and barrier thickness as effective routes for enhancing the TMR effect in all-two-dimensional magnetic tunnel junctions.

cond-mat.mtrl-sci↗

arXiv2026

Broken Symmetry-driven Weyl Semimetal Phase in Zn-Substituted EuMn$_2$Sb$_2$

The interplay between magnetism and electronic topology offers a powerful route to realizing emergent quantum phases. Here, we show that Zn substitution in the layered compound EuMn$_2$Sb$_2$ drives a transition from a C-type antiferromagnetic semiconductor to an intrinsic magnetic Weyl semimetal. Using first-principles calculations, we demonstrate that the parent compound hosts a gapped antiferromagnetic ground state, while Zn substitution alters the magnetic exchange interactions and stabilizes ferromagnetism. In the spin-orbit-coupled regime, the coexistence of broken time-reversal ($\mathcal{T}$) and inversion ($\mathcal{P}$) symmetries leads to the formation of Weyl nodes near the Fermi level. These nodes act as monopoles of Berry curvature and give rise to topologically protected Fermi-arc surface states. Our results identify EuMnZnSb$_2$ as a tunable platform where magnetism and topology are intrinsically coupled and establish chemical substitution as a viable strategy to engineer magnetic Weyl semimetals in correlated electron systems, with potential implications for spintronic and topological transport phenomena.

cond-mat.mtrl-sci↗

arXiv2026

Machine learning assisted High-Throughput study of M$_4$X$_3$T$_x$ MXenes

In this work, we employ a machine-learning-assisted high-throughput density functional theory framework to systematically investigate the stability, electronic structure, and magnetic ground states of 234 M$_4$X$_3$T$_x$ MXenes. The machine learning model predicts lattice parameters with up to 94% accuracy using a relatively small training dataset and significantly reduces structural optimization time in high-throughput calculations. Based on total energy and density-of-states analyses, we classify the magnetic nature of MXenes across different transition- metal compositions and surface terminations. Ti-, Zr-, Hf-, Nb-, and Ta-based MXenes are found to be non-magnetic metals for all functional groups considered, while Sc- and Y-based systems exhibit a range of behaviors including weak ferromagnetism and semiconducting character. V- and Fe-based MXenes are identified as antiferromagnetic metals, whereas Cr- and Mn-based MXenes yield 16 ferromagnetic systems with spin polarization ranging from 50% to 100%.

cond-mat.mtrl-sci↗

arXiv2025

Tunable Magnetic and Topological Phases in EuMnXBi$_2$ (X=Mn, Fe, Co, Zn) Pnictides

We present a comprehensive density functional theory (DFT) study of the electronic, magnetic, and topological properties of the layered pnictides EuMnXBi2 (X = Mn, Fe, Co, Zn), focusing in particular on the relatively unexplored Bi-based member of the EuMn2X2 family. Unlike the well-studied As-, Sb-, and P--based analogues, we show that EuMn2Bi2 stabilizes in a C-type antiferromagnetic ground state with a narrow-gap semiconducting character. Inclusion of spin-orbit coupling (SOC) drives a transition from this trivial antiferromagnetic semiconductor to a Weyl semimetal hosting four symmetry-related Weyl points and robust Fermi arc states. Systematic substitution of Mn with Fe, Co, and Zn further reveals a tunable sequence of magnetic ground states: Fe and Co induce ferrimagnetism with semimetallic behavior, while Zn stabilizes a ferromagnetic semimetal with a large net moment. These findings establish Bi-based EuMnXBi2 pnictides as a versatile platform where magnetic exchange interactions and band topology can be engineered through SOC and chemical substitution. The complex interplay of magnetic interactions and topological effects in the proposed bulk and doped pnictides opens a promising avenue to explore a wide range of electronic and magnetic phenomena. In particular, this study demonstrates that EuMn2Bi2 hosts tunable magnetic and topological phases driven by electron correlations, chemical substitution, and spin-orbit coupling.

cond-mat.mtrl-sci↗

arXiv2025

Four-fold Anisotropic Magnetoresistance in Antiferromagnetic Epitaxial Thin Films of MnPt$_{x}$Pd$_{1-x}$

Antiferromagnets are emerging as promising alternatives to ferromagnets in spintronics applications. A key feature of antiferromagnets is their anisotropic magnetoresistance (AMR), which has the potential to serve as a sensitive marker for the antiferromagnetic order parameter. However, the underlying origins of this behavior remains poorly understood, particularly, in thin film geometries. In this study, we report the observation of AMR in epitaxial thin films of the collinear L1$_{0}$ antiferromagnet MnPt$_{x}$Pd$_{1-x}$. In the thicker films, AMR is dominated by a non-crystalline two-fold component, which emerges from domain reconfiguration and spin canting under applied magnetic field. As the film thickness is reduced, however, a crystalline four-fold component emerges, accompanied by the appearance of uncompensated magnetic moment, which strongly modifies the magnetotransport properties in the thinner films. We demonstrate that interfacial interactions lead to a large density of states (DOS) at the Fermi level. This enhanced DOS, combined with disorder in the thinner films, stabilizes the uncompensated moment and results in a four-fold modulation of the DOS as the Neel vector rotates, explaining the observed AMR behavior.

cond-mat.mtrl-sci↗

arXiv2025

Symphony of Symmetry Selective Resonances in Fe-MgO-ZnO-MgO-Fe

We propose the perspective of symmetry-selective resonance of the $Δ_1$ states in the Fe/MgO/ZnO/MgO/Fe heterostructures, offering a broad landscape to design magnetic tunnel junctions (MTJs) that yield a towering tunnel magnetoresistance (TMR) up to $3.5\times10^4\%$ with the resistance area (RA) product dipping down to a minimum of $0.05~Ω\cdotμ\text{m}^2$, while maintaining a nearly perfect (99\%) spin polarization. Our predictions are based on the self-consistent coupling of the non-equilibrium Green's function with density functional theory. We also present the charge current, spin current, and TMR with applied voltage of the Fe/MgO(3-layer)/ZnO(3-layer)/MgO(3-layer)/Fe MTJ, which offers a superior performance triad of TMR ($1.3\times10^4\%$), RA ($0.45~Ω\cdotμ\text{m}^2$), and spin polarization (99\%) over a regular Fe/MgO(6-layer)/Fe based MTJ (TMR $\approx 3.4\times10^3\%$, RA $\approx 22~Ω\cdotμ\text{m}^2$). We provide a comprehensive insight integrating the transmission eigenchannel, spectral density, and the band structure of the Fe contacts to establish the role of symmetry-selective resonance in the Fe/MgO/ZnO/MgO/Fe MTJ.

cond-mat.mes-hall↗

arXiv2023

A review on multiscale computational studies for enhanced oil recovery using nanoparticles

Oil reservoirs around the globe are at their declining phase and in spite of enormous effectiveness of Enhanced Oil Recovery(EOR) in the Tertiary Stage. This process still bypasses some oil reason being surface forces responsible for holding oil inside the rock surface which are not being altered by the application of existing technologies. The processes coming under Tertiary Section Supplements primary and secondary sections. However, the mechanism of operating is different in both. Nanoparticles are showing a significant role in EOR techniques and is a promising approach to increase crude oil extraction. This is due to the fact that size of nanoparticles used for EOR lies in the range of 1-100 nm. It is also an interesting fact that in different operational conditions and parameters, the performance of nanoparticles also vary and some are more effective than others, which leads to various levels of recovery in the EOR process. In the present study, we intend to summarize a report having an up to date status on nanotechnology assisted EOR mechanisms where nanoparticles are used as nano-catalysts, nano-emulsions and nanoparticles assisted EOR mechanisms to destabilize the oil layer on carbonate surface. This review also highlights the various mechanisms such Gibb's free energy, wettability alteration, and Interfacial Tension Reduction (ITR) including interaction of available nanoparticles with reservoirs. Experimental measurements for a wide range of nanoparticles are not only expensive but are challenging because of the relatively small size, especially for the measurements of thinner capillaries of a nanoscale diameter. Therefore, we considered computational simulations as a more adequate approach to gain more microscopic insights into the oil displacement process to classify the suitability of nanomaterials.

cond-mat.mtrl-sci↗

arXiv2022

Pivotal Role of Intersite Hubbard Interactions in Fe-doped $α$-MnO$_2$

We present a first-principles investigation of the structural, electronic, and magnetic properties of the pristine and Fe-doped $α$-MnO$_2$ using density-functional theory with extended Hubbard functionals. The onsite $U$ and intersite $V$ Hubbard parameters are determined from first principles and self-consistently using density-functional perturbation theory in the basis of Löwdin-orthogonalized atomic orbitals. For the pristine $α$-MnO$_2$ we find that the so-called C2-AFM spin configuration is the most energetically favorable, in agreement with the experimentally observed antiferromagnetic ground state. For the Fe-doped $α$-MnO$_2$ two types of doping are considered: Fe insertion in the $2 \times 2$ tunnels and partial substitution of Fe for Mn. We find that the interstitial doping preserves the C2-AFM spin configuration of the host lattice only when both onsite $U$ and intersite $V$ Hubbard corrections are included, while for the substitutional doping the onsite Hubbard $U$ correction alone is able to preserve the C2-AFM spin configuration of the host lattice. The oxidation state of Fe is found to be $+2$ and $+4$ in the case of the interstitial and substitutional doping, respectively, while the oxidation state of Mn is $+4$ in both cases. This work paves the way for accurate studies of other MnO$_2$ polymorphs and complex transition-metal compounds when the localization of $3d$ electrons occurs in the presence of strong covalent interactions with ligands.

cond-mat.mtrl-sci↗

arXiv2021

Importance of intersite Hubbard interactions in $β$-MnO$_2$: A first-principles DFT+$U$+$V$ study

We present a first-principles investigation of the structural, electronic, and magnetic properties of pyrolusite ($β$-MnO$_2$) using conventional and extended Hubbard-corrected density-functional theory (DFT+$U$ and DFT+$U$+$V$). The onsite $U$ and intersite $V$ Hubbard parameters are computed using linear-response theory in the framework of density-functional perturbation theory. We show that while the inclusion of the onsite $U$ is crucial to describe the localized nature of the Mn($3d$) states, the intersite $V$ is key to capture accurately the strong hybridization between neighboring Mn($3d$) and O($2p$) states. In this framework, we stabilize the simplified collinear antiferromagnetic (AFM) ordering (suggested by the Goodenough-Kanamori rule) that is commonly used as an approximation to the experimentally-observed noncollinear screw-type spiral magnetic ordering. A detailed investigation of the ferromagnetic and of other three collinear AFM spin configurations is also presented. The findings from Hubbard-corrected DFT are discussed using two kinds of Hubbard manifolds - nonorthogonalized and orthogonalized atomic orbitals - showing that special attention must be given to the choice of the Hubbard projectors, with orthogonalized manifolds providing more accurate results than nonorthogonalized ones within DFT+$U$+$V$. This work paves the way for future studies of complex transition-metal compounds containing strongly localized electrons in the presence of pronounced covalent interactions.

cond-mat.mtrl-sci↗

arXiv2019

Asymmetric modification of the magnetic proximity effect in Pt/Co/Pt trilayers by the insertion of a Ta buffer layer

The magnetic proximity effect in top and bottom Pt layers induced by Co in Ta/Pt/Co/Pt multilayers has been studied by interface sensitive, element specific x-ray resonant magnetic reflectivity. The asymmetry ratio for circularly polarized x-rays of left and right helicity has been measured at the Pt $L_3$ absorption edge (11567 eV) with an in-plane magnetic field ($\pm158$ mT) to verify its magnetic origin. The proximity-induced magnetic moment in the bottom Pt layer decreases with the thickness of the Ta buffer layer. Grazing incidence x-ray diffraction has been carried out to show that the Ta buffer layer induces the growth of Pt(011) rather than Pt(111) which in turn reduces the induced moment. A detailed density functional theory study shows that an adjacent Co layer induces more magnetic moment in Pt(111) than in Pt(011). The manipulation of the magnetism in Pt by the insertion of a Ta buffer layer provides a new way of controlling the magnetic proximity effect which is of huge importance in spin-transport experiments across similar kind of interfaces.

cond-mat.mtrl-sci↗

arXiv2015

Teaching Python programming with automatic assessment and feedback provision

We describe a method of automatic feedback provision for students learning programming and computational methods in Python. We have implemented, used and refined this system since 2009 for growing student numbers, and summarise the design and experience of using it. The core idea is to use a unit testing framework: the teacher creates a set of unit tests, and the student code is tested by running these tests. With our implementation, students typically submit work for assessment, and receive feedback by email within a few minutes after submission. The choice of tests and the reporting back to the student is chosen to optimise the educational value for the students. The system very significantly reduces the staff time required to establish whether a student's solution is correct, and shifts the emphasis of computing laboratory student contact time from assessing correctness to providing guidance. The self-paced nature of the automatic feedback provision supports a student-centred learning approach. Students can re-submit their work repeatedly and iteratively improve their solution, and enjoy using the system. We include an evaluation of the system and data from using it in a class of 425 students.

cs.CY↗