arXiv subjects

Sandeep

Publications and source records attributed to Sandeep.

6 recordsLinked to original sources

arXiv2025

Intralayer antiferromagnetism in two-dimensional van der Waals magnet Fe$_3$GeTe$_2$

For the van der Waals magnet Fe$_3$GeTe$_2$, although a ferromagnetic ground state has been reported, there are also reports of complex magnetic behavior suggesting coexistence of ferromagnetism and antiferromagnetism due to the intricate interaction between Fe$^{+3}$ and Fe$^{+2}$ ions in this system. The exact nature of the interactions and the origin of antiferromagnetism are still under debate. Here, we report the observation of signature of ferromagnetic and antiferromagnetic couplings between different Fe-ions in the anomalous Hall effect measured for devices of mechanically exfoliated Fe$_3$GeTe$_2$ nano-flakes of thicknesses ranging from\,$\sim$\,15-20 layers. The temperature-dependent anomalous Hall effect data reveal two sharp step-like switchings at low temperature ($T\lesssim150\,$K). Our detailed analyses suggest the step-like sharp switchings in anomalous Hall resistance are due to the magnetization reversal behavior of different Fe-ions in individual layers of Fe$_3$GeTe$_2$. The experimental results can be explained by considering an intra-layer antiferromagnetic coupling between Fe$^{+3}$ and Fe$^{+3}$ ions, whereas intra-layer ferromagnetic coupling between Fe$^{+3}$ and Fe$^{+2}$ in the system. Our experimental results and the analyses are supported by the first-principles calculations for energetics and intralayer as well as interlayer exchange coupling constants.

cond-mat.mtrl-sci↗

arXiv2025

Optical contrast-based determination of number of layers for two-dimensional van der Waals magnet Fe$_3$GeTe$_2$

Recent advances in revealing intrinsic magnetism in two-dimensional (2D) materials have highlighted their potential for future spintronic applications, driven by their novel physical properties, promising for future spintronic devices. In order to explore layer dependent magnetic behavior, in general, mechanically exfoliated flakes from high-quality single crystals are used. It is crucial to determine the number of layers of these materials accurately. In the absence of an efficient and quick method, researchers often rely on atomic force microscopy (AFM) imaging to identify their number of layers. In this work, we report an optical contrast study as a quick and cost-effective technique to determine the number of layers of Fe$_3$GeTe$_2$ (FGT). Here, we observed a linear relationship between the optical contrast (derived from optical microscopic images) observed for mechanically exfoliated FGT nano-flakes and their thickness, as measured by the AFM imaging method. This technique requires no additional equipment; it relies solely on a conventional optical microscope. Additionally, our results reveal a thickness-dependent evolution of the intensity; in contrast, the Raman frequency demonstrates no significant dependence on layer thickness. Also, our studies reveal two additional Raman modes of FGT, at the frequency of 129\,cm$^-1$ \& 190\,cm$^-1$. Both modes show the intensity dependence on the thickness of FGT, same as out-of-plane (A$_{1g}$) Raman modes.

cond-mat.mtrl-sci↗

arXiv2025

Layer breathing Raman mode in two-dimensional van der Waals material $\mathrm{Cr_2Ge_2Te_6}$

Two-dimensional (2D) van der Waals (vdW) magnetic materials have emerged as key materials for next-generation magneto-electric and spintronic devices, where understanding the relationship between layer number, lattice dynamics, and magnetic interactions is very important. In this work, we report the observation of the layer breathing mode (LBM) in few-layer $\mathrm{Cr_2Ge_2Te_6}$, a ferromagnetic semiconductor with thickness dependent electronic, magnetic and optical properties, using Raman spectroscopy, which serves as a direct fingerprint of interlayer coupling and lattice symmetry. Group-theoretical symmetry analysis confirms that the CGT falls under the non-polar category of layered material. The evolution of the LBM-frequency with increasing layer number (N) reveals a distinct softening trend, characteristic of weakening restoring forces in thicker flakes. By fitting the experimental Raman data using the Linear Chain Model (LCM), we quantitatively extract the interlayer force constant ($\mathrm{K_c}$), providing a measure of the vdW coupling strength between layers.

cond-mat.mtrl-sci↗

arXiv2025

Biomarker Integration and Biosensor Technologies Enabling AI-Driven Insights into Biological Aging

As the global population continues to age, there is an increasing demand for ways to accurately quantify the biological processes underlying aging. Biological age, unlike chronological age, reflects an individual's physiological state, offering a more accurate measure of health-span and age-related decline. Aging is a complex, multisystem process involving molecular, cellular, and environmental factors and can be quantified using various biophysical and biochemical markers. This review focuses on four key biochemical markers that have recently been identified by experts as important outcome measures in longevity-promoting interventions: C-Reactive Protein, Insulin like Growth Factor-1, Interleukin-6, and Growth Differentiation Factor-15. With the use of Artificial Intelligence, the analysis and integration of these biomarkers can be significantly enhanced, enabling the identification of complex binding patterns and improving predictive accuracy for biological age estimation and age-related disease risk stratification. Artificial intelligence-driven methods including machine learning, deep learning, and multimodal data integration, facilitate the interpretation of high dimensional datasets and support the development of widely accessible, data-informed tools for health monitoring and disease risk assessment. This paves the way for a future medical system, enabling more personalized and accessible care, offering deeper, data-driven insights into individual health trajectories, risk profiles, and treatment response. The review additionally highlights the key challenges, and future directions for the implementation of artificial intelligence-driven methods in precision aging frameworks.

q-bio.QM↗

arXiv2024

A Multi-objective Economic Statistical Design of the CUSUM chart: NSGA II Approach

This paper presents an approach for the economic statistical design of the Cumulative Sum (CUSUM) control chart in a multi-objective optimization framework. The proposed methodology integrates economic considerations with statistical aspects to optimize the design parameters like the sample size ($n$), sampling interval ($h$), and decision interval ($H$) of the CUSUM chart. The Non-dominated Sorting Genetic Algorithm II (NSGA II) is employed to solve the multi-objective optimization problem, aiming to minimize both the average cost per cycle ($C_E$) and the out-of-control Average Run Length ($ARL_\delta$) simultaneously. The effectiveness of the proposed approach is demonstrated through a numerical example by determining the optimized CUSUM chart parameters using NSGA II. Additionally, sensitivity analysis is conducted to assess the impact of variations in input parameters. The corresponding results indicate that the proposed methodology significantly reduces the expected cost per cycle by about 43% when compared to the findings of the article by M. Lee in the year 2011. A more extensive comparison with respect to both $C_E$ and $ARL_\delta$ has also been provided for justifying the methodology proposed in this article. This highlights the practical relevance and potential of this study for the right application of the technique of the CUSUM chart for process control purposes in industries.

stat.AP↗

arXiv2014

Half metallic ferromagnetism in tri-layered perovskites Sr$_4$T$_{3}$O$_{10}$ (T=Co, Rh)

First-principles density functional theory (DFT) is used to investigate the electronic and magnetic properties of Sr$_4$Rh$_3$O$_{10}$, a member of the Ruddlesden-Popper series. Based on the DFT calculations taking into account the co-operative effect of Coulomb interaction ($U$) and spin-orbit couplings (SOC), Sr$_4$Rh$_3$O$_{10}$ is found to be a half metallic ferromagnet (HMF) with total angular moment $\mu_{\rm {tot}}$=12$\mu_B$ per unit cell. The material has almost 100$\%$ spin-polarization at the Fermi level despite of sizable SOC. Replacement of Rh atom by the isovalent Co atom is considered. Upon full-replacement of Co, a low-spin to intermediate spin transition happens resulting in a HMF state with the total angular moment three-time larger (i.e. $\mu_{\rm {tot}}$=36$\mu_B$ per unit cell), compared to Sr$_4$Rh$_3$O$_{10}$. We propose Sr$_4$Rh$_3$O$_{10}$ and Sr$_4$Co$_3$O$_{10}$ as candidates of half metals.

cond-mat.mtrl-sci↗