arXiv subjects

Fariba Nazari

Publications and source records attributed to Fariba Nazari.

5 recordsLinked to original sources

arXiv2025

Enhancing Magnetic Coupling in MN4-Graphene via Strain Engineering

MN4-embedded graphene (MN4-G) layers, incorporating transition metal elements (M), represent a class of experimentally accessible two-dimensional materials with significant potential for stable nanoscale magnetization. In these systems, magnetic exchange interactions are primarily governed by Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling, exhibiting an anomalously prolonged decay of r to the power of (-n), where r is the M-M separation distance and n is between 0.5 and 2. This study investigates the impact of strain on the electronic and magnetic properties of MN4-G layers using ab-initio density functional theory (DFT). A novel strain-engineering approach is developed by applying controlled tension or compression to the layers. Our findings reveal that strain significantly modulates the strength, amplitude, and decay rate of the RKKY coupling. Notably, the CoN4-G layer demonstrates a pronounced enhancement in RKKY coupling strength, oscillation amplitude, and reduced decay rate under strain. Conversely, the CuN4-G layer exhibits distinct behavior, maintaining decoupled spin chains and invariant electronic and magnetic properties despite applied strain. This work underscores the tunability of magnetic interactions in MN4-G layers via strain engineering, providing insights into the design of strain-controlled magnetic materials for next-generation spintronic applications.

cond-mat.mtrl-sci↗

arXiv2025

Tuning topologically nontrivial states in the BHT-Ni metal organic framework

Using first principles calculations, we have demonstrated the creation of multiple quantum states, in the experimentally accessible metal organic framework BHT-Ni. Specifically, quantum spin Hall and quantum anomalous Hall states are induced by two and four electron doping, respectively. The geometrical symmetry breaking, is also investigated. For a low electron doping concentration of two electrons per unit cell, the Fermi energy shifts to a nontrivial band gap, between Dirac bands and a quantized spin Hall conductivity is predicted. Subsequently in a high electron doping concentration, Anomalous Hall conductivity with a quantized value was observed. In addition, for centrosymmetric (trans-like) and non-centrosymmetric (cis-like) structures, we found that the trans-like structure preserves quantum spin Hall and quantized spin Hall conductivity. In contrast, in the cis-like structure, space inversion symmetry breaking leads to the appearance of valley Hall effect and the disappearance of spin Hall conductivity.

cond-mat.mtrl-sci↗

arXiv2024

Uncovering Electronic Exchange Behavior: Exploring Insights from Simple Models

Exchange couplings are fundamental to our understanding of many physical phenomena in condensed matter physics and material science. Model systems provide a controlled environment to investigate such phenomena, effectively. In this study, we employ first-principle calculations based on density functional theory and Green's function (GF) method to explore the impact of chemical structure on the sign and magnitude of exchange coupling, systematically. By designing model systems with bcc-Fe bulk doped with nonmagnetic X= (H, B, C, N, O, and F) atoms, we examine the effects of different ligands on the behavior of Fe-Fe exchange coupling, and demonstrate that the chemical environment surrounding the metal atom significantly influences the Fe-Fe exchange coupling. Our results highlight the tunability of exchange coupling based on Fe-dopant bond length(s), where the nature of ligand atoms and their electron correlation play a crucial role. This work illuminates the complex relationship between structure, and magnetism in magnetic materials, providing insights into the development of high-performance magnetic materials.

cond-mat.mtrl-sci↗

arXiv2022

MN4 Embedded Graphene Layers: Tunable Decay Rate of RKKY Interaction

One of the most important tasks in the development of high-performance spintronic devices is the preparation of two dimensional (2D) magnetic layers with long-range exchange interactions. MN4 embedded graphene (MN4-G) layers, with M being transition metal elements, are experimentally accessible 2D layers, which exhibit interesting magnetic properties. In this paper, by employing the spin-polarized density functional theory (SP-DFT), we study MN4-G layers with a special focus on the behavior of the indirect M-M exchange interactions, and demonstrate that the MN4-Gs with M = Fe, Mn and Co, are 2D anisotropic magnetic layers with Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. By examining the electronic configurations of the M atoms for various M-M spacers, we demonstrate that the RKKY interaction in such layers are tunable and exhibiting an unusual prolonged decay (r to the power of minus n, n between 0.5 and 2). In addition, we investigate the influence of the CuN4 moiety in the graphene host, and show that, in contrary to the other MN4-Gs, the 2D CuN4-G layer behaves as decoupled one-dimensional spin chains, regardless of the spacer lengths.

cond-mat.mtrl-sci↗

arXiv2017

Prediction of many-electron wavefunctions using atomic potentials

For a given many-electron molecule, it is possible to define a corresponding one-electron Schrödinger equation, using potentials derived from simple atomic densities, whose solution predicts fairly accurate molecular orbitals for single- and multi-determinant wavefunctions for the molecule. The energy is not predicted and must be evaluated by calculating Coulomb and exchange interactions over the predicted orbitals. Potentials are found by minimizing the energy of predicted wavefunctions. There exist slightly less accurate average potentials for first-row atoms that can be used without modification in different molecules. For a test set of molecules representing different bonding environments, these average potentials give wavefunctions with energies that deviate from exact self-consistent field or configuration interaction energies by less than 0.08 eV and 0.03 eV per bond or valence electron pair, respectively.

physics.chem-ph↗