arXiv subjects

Rohit Pathak

Publications and source records attributed to Rohit Pathak.

6 recordsLinked to original sources

arXiv2026

Magnetic frustration and non-collinear textures in layered Gd magnets

Using scale-bridging simulations based on electronic structure theory and atomistic spin dynamics, we investigate the magnetic properties of skyrmionic GdRu$_2$Si$_2$ and GdRu$_2$Ge$_2$ layered rare-earth magnets and similar Gd-based compounds (GdAu$_2$Si$_2$, GdAu$_2$Ge$_2$, GdAg$_2$Si$_2$ and GdAg$_2$Ge$_2$). By studying the trends across this structural family, we confirm the importance of magnetic frustration and dipolar interactions for the stability of non-collinear and skyrmion phases. Furthermore, our calculations predict promising opportunities for chemical tuning of these magnets in terms of the balance between various exchange interactions and the character of the magnetic anisotropy. These changes lead to the formation of new types of skyrmions that are stable in a wide range of applied external magnetic field. In particular, we propose partial alkali-metal substitution of Gd in GdRu$_2$Si$_2$ leading to GdKRu$_4$Si$_4$, GdRbRu$_4$Si$_4$, GdCsRu$_4$Si$_4$ as well as GdYRu$_4$Si$_4$ compounds, and suggest that it is likely to result in an ordered layered structure, similarly to previously reported iron pnictides like CaKFe$_4$As$_4$.

cond-mat.mtrl-sci↗

arXiv2026

Mechanical control of magnetic exchange and response in GdRu$_2$Si$_2$: A computational study

We present a systematic computational study of the effect of uniaxial strain on the magnetic properties of GdRu$_2$Si$_2$, a centrosymmetric material known to host a field-induced skyrmion lattice (SkL). Using first-principles density functional theory, we first demonstrate the pronounced sensitivity of the exchange and anisotropy to specific structural distortions. These DFT-derived interactions are then integrated into a classical spin model to construct comprehensive magnetic phase diagrams under both compressive and tensile strain. Our key finding is that compressive strain ($\sim 2\%$) acts as an effective tuning parameter, substantially expanding the stability region of the $\vec Q_{100}$-driven topologically nontrivial phases. This results from the shifts in the critical magnetic fields and enhancement of the energy scale of the favored magnetic wave vector. In contrast, tensile strain induces a different magnetic ground-state by promoting a different magnetic ordering vector, $\vec Q_{110}$, leading to entirely distinct phase behavior. This work not only provides a quantitative understanding of the structural-magnetic coupling in GdRu$_2$Si$_2$ but also establishes strain engineering as a powerful approach to control and optimize topologically non-trivial magnetic phases in centrosymmetric magnets.

cond-mat.mtrl-sci↗

arXiv2025

Tailoring hard magnetic properties of Fe2MnSn Heusler alloy via interstitial modification: A first-principles approach

We employ first-principles calculations to explore interstitial engineering as a strategy to tailor the hard magnetic properties of Fe2MnSn Heusler alloy, establishing its potential as a rare-earth-free permanent magnet. By introducing light interstitial elements -- B, C, H, N, O, and F -- at varying concentrations (1.56-12.5 at%), we uncover significant enhancements in structural stability, magnetization, Curie temperature, and magnetocrystalline anisotropy. These dopants preferentially occupy octahedral interstitial sites in the hexagonal phase of Fe2MnSn, leading to localized lattice distortions that enhance its magnetic characteristics. Notably, at 12.5 at% doping, B, C, N, and O induce a critical transition from in-plane to out-of-plane magnetic anisotropy -- achieved without 5d or rare-earth elements -- highlighting a sustainable pathway to high-performance magnets. Among these, N-doped Fe2MnSn exhibits the highest uniaxial anisotropy (0.61 MJ/m^3), followed by the B-doped (0.44 MJ/m^3) alloy. The magnetization of the doped compounds surpasses that of conventional ferrites and gap magnets like MnAl and MnBi. The Curie temperature sees a substantial boost, reaching 1058 K for O-doped Fe2MnSn and 1000 K for the C-doped alloy. Although N-doping results in a modest increase in Tc (744 K vs. 729 K for the pristine alloy), it delivers superior hard magnetic properties, with the highest magnetic hardness (0.65) and an enhanced maximum energy product (0.36 MJ/m^3), making it a strong candidate for gap magnet applications. These findings highlight interstitial doping as a viable route to engineer rare-earth-free permanent magnets with optimized magnetic performance.

cond-mat.mtrl-sci↗

arXiv2025

Ultrafast demagnetization dynamics of 4f antiferromagnets

We study the ultrafast demagnetization dynamics of LnRh$_2$Si$_2$ (Ln $=$ Pr, Nd, Sm, Gd, Tb, Dy, Ho) antiferromagnets (AFM) after excitation by a laser pulse, using a combination of density functional theory and atomistic spin and spin-lattice dynamics simulations. First, we calculate the Heisenberg interactions using the magnetic force theorem and compare two approaches, where the $4f$ states of the rare earths are treated as frozen core states or as valence states with added correlation corrections. We find marked quantitative differences in terms of predicted Curie temperature for most of the systems, especially for those with large orbital moment of the rare earth cations. This can be attributed to the importance of indirect interactions of the $4f$ states through the Si states, which depend on the binding energy of the $4f$ states and coexists with RKKY-type interactions mediated by the conduction states. However, qualitatively, both approaches agree in terms of the predicted AFM ordering at low temperatures. In the second step, the atomistic dynamics simulations are combined with a heat-conserving two-temperature model, allowing for the calculation of spin and electronic temperatures during the magnetization dynamics simulations. Despite quite different demagnetization times, magnetization dynamics of all studied LnRh$_2$Si$_2$ AFM exhibit similar two-step behavior, in particular, the first fast drop followed by slower demagnetization. We observe that the demagnetization amplitude depends linearly on laser fluence for low fluences, which is in agreement with experimental observations. We also investigate the impact of lattice dynamics on ultrafast demagnetization using coupled atomistic spin-lattice dynamics simulations and a heat-conserving three-temperature model, which confirm linear dependence of magnetisation on laser fluence.

cond-mat.mtrl-sci↗

arXiv2024

Unveiling Mysteries of GdRu$_2$Si$_2$: 3D Magnetism in a layered like Magnet

GdRu$_2$Si$_2$, a centrosymmetric magnet with a square lattice of Gd atoms, hosts a short-period skyrmion square lattice (SkL) without Dzyaloshinskii-Moriya interaction (DMI). RKKY-type exchange between the Gd moments results in an exchange frustration, which is the main source of non-collinearity in the spiral phases of the system. Previous studies focused on the in-plane $\vec{Q}$ vectors in understanding the magnetic phases of the system as they appear and have been observed on the 2D Gd layers. In this work, we calculate the Gd-Gd magnetic exchange interactions ($J_{ij}$) and perform atomic spin dynamics (ASD) simulations, providing new insights about GdRu$_2$Si$_2$. Our calculated $J_{ij}$ shows that the strongest magnetic interaction occurs between Gd atoms along the [111] body-diagonal direction of the unit cell. This, along with the body-centered tetragonal structure of the Gd sublattice, points to the presence of a hitherto ignored modulation vector, $\vec{Q}_{[111]}$, along the [111] direction in the spiral phases of the system. ASD simulations confirm this interlayer modulation, demonstrating that GdRu$_2$Si$_2$'s magnetic phases are more complex than suggested by 2D layer observations. The total magnetic order is determined by $\vec{Q}_{[111]}$ alongside intralayer $\vec{Q}_{[100]}$ and $\vec{Q}_{[010]}$, establishing GdRu$_2$Si$_2$ as a strong 3D magnet requiring comprehensive theoretical modeling. Considering these, our ASD simulations accurately reproduce experimental phase transitions and highlight the significant role of dipolar interactions (due to the large Gd moment) over a weak uniaxial anisotropy in determining the ground state. This work enhances the understanding of GdRu$_2$Si$_2$'s complex magnetism, suggesting similar interlayer effects may be important in other layered magnetic systems.

cond-mat.mtrl-sci↗

arXiv2022

A strategic high throughput search for identifying stable Li based half Heusler alloys for spintronics applications

In this work, high throughput DFT calculations are performed on the alkali metal-based half Heusler alloys; LiY$_p$Y$^\prime_{1-p}$S (Y, Y$^\prime$ = V, Cr, Mn, Fe, Co, Ni and $\mathit{p}$ = 0, 0.25, 0.5, 0.75, 1). Starting with 243 structural replica, systematic filters are designed to select the energetically and vibrationally favorable compositions by considering the contributions stemming from the magnetic alignments of the ions. Thereby, 26 dynamically stable magnetic compositions are identified, of which 10 are found to be ferromagnetic (FM), 4 antiferromagnetic (AFM) and 12 ferrimagnetic (FiM). 4 FM and 8 FiM ones are found to show 100 $\%$ spin polarization. Further, tetragonal distortion is found to be present in 4 FM, 3 FiM and 4 AFM compositions, which indicates the possibility of easy-axis magnetocrystalline anisotropy. The ferromagnetic LiFe$_{0.5}$Mn$_{0.5}$S and antiferromagnetic LiFeS are found to have the most prominent easy-axis magnetocrystalline anisotropy.

cond-mat.mtrl-sci↗