arXiv subjects

Ali Ghojavand

Publications and source records attributed to Ali Ghojavand.

4 recordsLinked to original sources

arXiv2025

Benchmarking First-Principles Approaches for Extracting Magnetic Exchange Interactions

Magnetic exchange interactions govern the macroscopic magnetic behavior of solids and underpin both fundamental spin phenomena and emerging technologies. The accurate and efficient determination of these interactions is therefore critical for predictive modeling of magnetic materials. Here we present a systematic first-principles comparison of three widely used approaches-the Least-Squares Total Energy (LSTE), the Four-State Total Energy (FSTE), and the Green's function-based Liechtenstein \textit{et al.} (LKAG) methods-applied to thirteen antiferromagnetic compounds. We introduce an framework for identifying the minimal supercells required for an accurate exchange parameter extraction in the FSTE method, significantly reducing computational cost while preserving precision. Our results show that LSTE and FSTE yield nearly identical exchange parameters, whereas the LKAG method reproduces the dominant exchange interactions but exhibits quantitative deviations. A detailed analysis of computational efficiency versus accuracy reveals that the LSTE scheme offers the most favorable balance, establishing a general, reproducible, and scalable workflow for Heisenberg mapping, while the FSTE approach remains the most straightforward for extracting specific exchange interactions.

cond-mat.mtrl-sci↗

arXiv2025

Strain-tuned magnetoelectric properties of monolayer NiX$_2$ (X = I, Br): a first-principles analysis

Using \textit{ab initio} methodology, we reveal a strain-mediated approach to precisely tune the magnetoelectric coupling and spin-driven emergent polarization of NiX$_2$ (X = I, Br) monolayers. In the absence of strain, these systems spontaneously stabilize non-collinear spin states that break the inversion symmetry, inducing a ferroelectric polarization in the plane of the material. We show that biaxial and uniaxial strains broadly modulate the magnetoelectric response in these materials through two distinct mechanisms: (i) direct modification of the magnetoelectric tensor components, and (ii) tuning of the characteristic propagation vectors of a spin texture. This dual mechanism enables precise control over the magnitude of the spin-induced electric polarization of these materials. With respect to the achievable magnitude of the electric polarization, we demonstrate the critical role of third-nearest-neighbor spin-pair contributions, which can increase under strain to levels that compete with or even exceed the polarization driven by first-nearest-neighbor effects. These findings offer important insights into low-dimensional piezo-magnetoelectricity and expand the possibilities for designing multifunctional two-dimensional straintronic devices.

cond-mat.mtrl-sci↗

arXiv2024

Strain-tunable magnetic and magnonic states in Ni-dihalide monolayers

Monolayer NiI$_2$ garners large research interest due to its multiferroic behavior stemming from the interplay between its non-collinear magnetic order and the spin-orbit coupling. This prompts an investigation into the stability of the magnetic order in NiI$_2$ and similar materials under external stimuli. In this work, we report the effect of biaxial and uniaxial strain on the magnetic ground state, the critical temperature, and the magnonic properties of the NiX$_2$ (X = I, Br, Cl) monolayers. For all three materials, we reveal intricate strain-dependent phase diagrams, including ferromagnetic, helimagnetic, and skyrmionic phases. Moreover, we discuss the necessity of considering the biquadratic exchange interaction in the latter analysis. We reveal that the biquadratic exchange significantly alters both the magnetic ground state and the critical temperature of the magnetic order, and we demonstrate that its importance becomes even more explicit when monolayer Ni-dihalides are strained. Finally, we calculate the magnonic dispersion for the predicted magnetic states, showing that the skyrmionic phase functions as a magnonic crystal, and demonstrate the presence of strain-tunable soft magnon modes at finite wavevectors in the helimagnetic phase.

cond-mat.mes-hall↗

arXiv2020

Ab initio analysis of some Ge-based 2D nanomaterials

The structural, electronic and dynamical properties of a group of 2D germanium-based compounds, including GeC, GeN, GeO, GeSi, GeS, GeSe, and germanene, are investigated by employing first-principles calculations. The most stable structure of each of these systems is identified after considering the most probable configurations and performing accurate phonon calculations. We introduce a new phase of germanene, which we name the tile germanene, which is significantly more stable than the known hexagonal germanene. We apply the modern modified Becke-Johnson (mBJ) and DFT1/2 schemes to obtain an accurate band structure for our selected 2D materials. It is seen that GeO and GeC exhibit the highest band gaps of more than 3 eV in this group of materials. Moreover, we argue that, in contrast to the semi-metallic nature of hexagonal germanene, the tile germanene is a very good conductor. The band edges of our semiconducting 2D materials are accurately aligned to the vacuum level to address the potential photocatalytic application of this system for water splitting and carbon dioxide reduction. The optical properties, including dielectric functions, refractive index, reflectivity, and Loss function of the samples are investigated in the framework of the Bethe-Salpeter approach.

cond-mat.mtrl-sci↗