arXiv subjects

Shivani Kumawat

Publications and source records attributed to Shivani Kumawat.

4 recordsLinked to original sources

arXiv2026

Transition metal (group V) doping induced spin and valley polarization in MoS$_2$ monolayer

Doping in two-dimensional materials has emerged as an effective tool for modulating their electronic properties and thereby enabling their multifunctional applications. In this work, we present a first-principles study on induced effective magnetic moment and metallicity in MoS$_2$ monolayer by substitutional doping of group-5 transition metal (TM) elements -- V, Nb and Ta. From our study, we observe that the V doping induces half-metallicity, whereas metallic characteristics are observed in the case of Nb and Ta doping. Moreover, V and Ta-doped MoS$_2$ monolayers are observed to show total induced magnetic moments of 0.922 and 0.624 $μ_{\rm B}$, respectively. Importantly, the combined effects of strong spin-orbit coupling (SOC), broken inversion symmetry, and structural asymmetry is observed to lead to a permanent valley polarization in the V- and Ta-MoS$_2$ systems. In particular, we observed a valley polarization of 121 and 21 meVs for V and Ta-doped MoS$_2$, respectively. Furthermore, an enhanced piezoelectric coefficient for the doped systems is observed compared to pristine MoS$_2$. Notably, the simultaneous presence of half-metallicity, substantial valley polarization, and enhanced piezoelectricity in V-doped MoS$_2$ establishes this system as a promising multifunctional platform for next-generation spintronic, valleytronic, and piezoelectric nanodevices. Overall, our findings provide fundamental insights into engineering coupled spin-valley-mechanical degrees of freedom in two-dimensional materials for advanced quantum and nanoelectronic applications.

cond-mat.mtrl-sci↗

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↗

arXiv2024

Emergence of half-metallic ferromagnetism and valley polarization in transition metal substituted WSTe monolayer

Two-dimensional (2D) Janus materials hold a great importance in spintronic and valleytronic applications due to their unique lattice structures and emergent properties. They intrinsically exhibit both an in-plane inversion and out-of-plane mirror symmetry breakings, which offer a new degree of freedom to electrons in the material. One of the main limitations in the multifunctional applications of these materials is, however, that, they are usually non-magnetic in nature. Here, using first-principles calculations, we propose to induce magnetic degree of freedom in non-magnetic WSTe via doping with transition metal (TM) elements -- Fe, Mn and Co. Further, we comprehensively probe the electronic, spintronic and valleytronic properties in these systems. Our simulations predict intrinsic Rashba and Zeeman-type spin splitting in pristine WSTe. The obtained Rashba parameter is $\sim$ 422 meVÅ\; along the $Γ- K$ direction. Our study shows a strong dependence on uniaxial and biaxial strains where we observe an enhancement of $\sim$ 2.1\% with 3\% biaxial compressive strain. The electronic structure of TM-substituted WSTe reveals half-metallic nature for 6.25 and 18.75\% of Fe, 25\% of Mn, and 18.75 and 25\% of Co structures, which leads to 100\% spin polarization. The obtained values of valley polarization 65, 54.4 and 46.3 meV for 6.25\% of Fe, Mn and Co, respectively, are consistent with the literature data for other Janus materials. Further, our calculations show a strain dependent tunability of valley polarization, where we find an increasing (decreasing) trend with uniaxial and biaxial tensile (compressive) strains. We observed a maximum enhancement of $\sim$ 1.72\% for 6.25\% of Fe on application of 3\% biaxial tensile strain.

cond-mat.mtrl-sci↗

arXiv2024

Antiferromagnetic weak topological state in Bismuth square-net based nonsymmorphic lattice

The ZrSiS-class of layered materials offer interesting topological and magnetic characteristics suitable for spintronics applications. In this work, we have synthesized a polycrystalline NdBiTe using solid-state reaction technique and have examined the magnetic properties in 2 - 300 K temperature range using temperature and field-dependent magnetization measurements. Our magnetic and specific heat data demonstrates a long-range antiferromagnetic ordering in the material below 4.5 K. Furthermore, our isothermal magnetization data show a signature of spin-reorientation below Neel temperature. The observed nonlinearity in inverse susceptibility vs temperature data, and a hump in specific heat in 5-20 K range, indicate the existence of crystal field splitting in the material. Our transport properties measurements show the metallic behavior with positive magnetoresistance in the temperature range of 2 - 300 K. The observed rise in resistivity as function of temperature below Neel temperature infers the strongly correlated fermions, which is consistent with the observed large Sommerfeld coefficient. Consistent with experimental results, our first-principles calculations predict an antiferromagnetic semimetallic nature of NdBiTe. Further, our spin-orbit coupled simulations of electronic structure show a signature of weak topological nature of the material.

cond-mat.str-el↗