arXiv subjects

Gaurav K. Shukla

Publications and source records attributed to Gaurav K. Shukla.

9 recordsLinked to original sources

arXiv2026

Efficient magnetization switching driven by orbital torque originating from light 3d-transition-metal nitrides

The orbital Hall effect (OHE) in light transition metals offers a promising route to generate orbital torques for efficient magnetization control, providing an alternative to conventional spin Hall effect approaches that rely on heavy metals. We demonstrate perpendicular magnetization switching in [Co/Pt]3 multilayers driven by the OHE in a light 3d transition metal nitride, VN, with 111-texture of face-center cubic structure. Second harmonic Hall measurement reveals a large torque efficiency of -0.41 in the VN(7.5 nm)/[Co(0.35nm)/Pt(0.3 nm)]3, which significantly surpasses that in the control samples with Co, Py, and CoFeB ferromagnets, suggesting strong conversion of orbital current originating from VN to spin current by [Co/Pt]3 ferromagnet. Full switching by in-plane current is achieved with an in-plane magnetic field, while partial field-free switching occurs without it. The critical current density for the switching is found to be comparable to that of the W-based spin-orbit torque device. First-principles calculations confirm a large orbital Hall conductivity in VN, with a small spin Hall conductivity around the Fermi energy. Our results highlight the potential in the combination of light 3d transition metal nitrides and Co/Pt ferromagnetic multilayer with 111-texture to maximize the magnetization switching efficiency of orbitronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Unconventional Spin-orbit Torques by Two-dimensional Multilayered MXenes for Future Nonvolatile Magnetic Memories

MXenes have attracted considerable attention in recent years owing to their two-dimensional (2D) layered structures with various functionalities similar to those of graphene and transition metal dichalcogenides. To open a new application field for MXenes in the realm of electronic devices, such as ultrahigh-integrated magnetic memory, we have developed a spin-orbit torque (SOT) bilayer structure comprising bare MXene of Cr2N: substrate//Cr2N/[Co/Pt]3/MgO using the magnetron sputtering technique. We demonstrated field-free current-induced magnetization switching (CIMS) in the bilayer structure, regardless of the charge current directions with respect to the mirror symmetry lines of Cr2N crystal. This is a specific characteristic for the 2D MXene-based SOT-devices, originating from an unconventional out-of-plane SOT. As the SOT efficiency increases with increasing the Cr2N thickness, the first-principles calculations predict an intrinsic orbital-Hall conductivity with the dominant out-of-plane component, comparing to the spin-Hall conductivity in the Cr2N. X-ray magnetic circular dichroism reveals the out-of-plane uncompensated magnetic moment of Cr in the Cr2N layer at the interface, induced by contact with the Co in the [Co/Pt]3 ferromagnetic layer. Therefore, the intrinsic bulk orbital Hall effect in MXene and the interfacial contribution such as spin-filtering-like effect owing to uncompensated magnetic moment of Cr are considered as possible major mechanisms for the unconventional out-of-plane SOT in the device, rather than a crystal symmetry and/or an interlayer exchange coupling.

cond-mat.mes-hall↗

arXiv2025

Berry curvature-induced intrinsic spin Hall effect in light-element-based CrN system for magnetization switching

The current-induced spin-orbit torque-based devices for magnetization switching are commonly relied on the 4d and 5d heavy metals owing to their strong spin-orbit coupling (SOC) to produce large spin current via spin Hall effect (SHE). Here we present the sizable SHE in CrN, a light element-based system and demonstrate the current-induced magnetization switching in the adjacent ferromagnetic layer [Co(0.35nm)/Pt(0.3nm)]3, which exhibits perpendicular magnetic anisotropy. We found the switching current density of 2.6 MA/cm2. The first principles calculation gives the spin Hall conductivity (SHC) to be 120 (hcross/e) S/cm due to intrinsic Berry curvature arising from SOC induced band splitting near Fermi-energy. The theoretically calculated intrinsic SHC is close to the experimental SHC extracted from second harmonic Hall measurement. We estimated spin Hall angle to be 0.09, demonstrating efficient charge-to-spin conversion in CrN system.

cond-mat.mtrl-sci↗

arXiv2023

Colossal anomalous Hall and Nernst effect from the breaking of nodal-line symmetry in Cu2CoSn Weyl semimetal: A first-principles study

The presence of topological band crossings near the Fermi energy is essential for the realization of large anomalous transport properties in the materials. The topological semimetals (TSMs) host such properties owing to their unique topological band structure such as Weyl points or nodal lines (NLs), that is protected by certain symmetries of the crystal. When the NLs break out in the system due to perturbation in Hamiltonian, a large Berry curvature arises in the surrounding area of the gapped NL. In the present work, we studied anomalous transport properties of Cu2CoSn compound, which has a cubic Heusler crystal structure (space group: Fm-3m). The Cu2CoSn full Heusler compound possesses three NLs in the absence of spin-orbit coupling close to the Fermi level. These NLs gap out with the consideration of the SOC and a large Berry curvature observed along the gapped NLs. The integral of Berry curvature gives the intrinsic anomalous Hall conductivity (AHC) about 1003 S/cm and the anomalous Nernst conductivity (ANC) of about 3.98 A/m-K at the Fermi level. These values of AHC and ANC are comparable to the largest reported values for the Co2MnGa Heusler compound. Therefore, Cu2CoSn becomes a newborn member of the family of full Heusler compounds, which possesses giant AHC and ANC that can be useful for the spintronics application.

cond-mat.mtrl-sci↗

arXiv2022

Anti-site disorder and Berry curvature driven anomalous Hall effect in spin gapless semiconducting Mn2CoAl Heusler compound

Spin gapless semiconductors exhibit a finite band gap for one spin channel and closed gap for other spin channel, emerged as a new state of magnetic materials with a great potential for spintronic applications. The first experimental evidence for the spin gapless semiconducting behavior was observed in an inverse Heusler compound Mn2CoAl. Here, we report a detailed investigation of the crystal structure and anomalous Hall effect in the Mn2CoAl using experimental and theoretical studies. The analysis of the high-resolution synchrotron x-ray diffraction data shows anti-site disorder between Mn and Al atoms within the inverse Heusler structure. The temperature-dependent resistivity shows semiconducting behavior and follows Mooijs criteria for disordered metal. Scaling behavior of the anomalous Hall resistivity suggests that the anomalous Hall effect in the Mn2CoAl is primarily governed by intrinsic mechanism due to the Berry curvature in momentum space. The experimental intrinsic anomalous Hall conductivity (AHC) is found to be 35 S/cm, which is considerably larger than the theoretically predicted value for ordered Mn2CoAl. Our first-principle calculations conclude that the anti-site disorder between Mn and Al atoms enhances the Berry curvature and hence the value of intrinsic AHC, which is in a very well agreement with the experiment.

cond-mat.mtrl-sci↗

arXiv2022

Band splitting induced Berry flux and intrinsic anomalous Hall conductivity in NiCoMnGa quaternary Heusler compound

The anomalous transport properties of Heusler compounds become a hotspot of research in recent years due to their unique band structure and possible application in spintronics. In this paper, we report the anomalous Hall effect in polycrystalline NiCoMnGa quaternary Heusler compound by experimental means and theoretical calculations. The experimental anomalous Hall conductivity (AHC) was found at about 256 S/cm at 10K with an intrinsic contribution of ~ 121 S/cm. The analysis of Hall data reveals the presence of both extrinsic and intrinsic contributions in AHE. Our theoretical calculations show that a pair of spin-orbit coupled band formed by the band splitting due to spin-orbit interaction (SOI) at the Fermi level produces a finite Berry flux in the system that provides the intrinsic AHC about 100 S/cm, which is in good agreement with the experiment.

cond-mat.mtrl-sci↗

arXiv2022

Role of chemical disorder in tuning the Weyl points in vanadium doped Co$_2$TiSn

The lack of time-reversal symmetry and Weyl fermions give exotic transport properties to Co-based Heusler alloys. In the present study, we have investigated the role of chemical disorder on the variation of Weyl points in Co\textsubscript{2}Ti\textsubscript{1-x}V\textsubscript{x}Sn magnetic Weyl semimetal candidate. We employ the first principle approach to track the evolution of the nodal lines responsible for the appearance of Weyl node in Co$_2$TiSn as a function of V substitution in place of Ti. By increasing the V concentration in place of Ti, the nodal line moves toward Fermi level and remains at Fermi level around the middle composition. Further increase of the V content, leads shifting of nodal line away from Fermi level. Density of state calculation shows half-metallic behavior for the entire range of composition. The magnetic moment on each Co atom as a function of V concentration increases linearly up to x=0.4, and after that, it starts decreasing. We also investigated the evolution of the Weyl nodes and Fermi arcs with chemical doping. The first-principles calculations reveal that via replacing almost half of the Ti with V, the intrinsic anomalous Hall conductivity increased twice as compared to the undoped composition. Our results indicate that the composition close to the 50\% V doped Co$_2$TiSn, will be an ideal composition for the experimental investigation of Weyl physics.

cond-mat.mtrl-sci↗

arXiv2022

Atomic disorder and Berry phase driven anomalous Hall effect in Co2FeAl Heusler compound

Co2-based Heusler compounds are the promising materials for the spintronics application due to their high Curie temperature, large spin-polarization, large magnetization density, and exotic transport properties. In the present manuscript, we report the anomalous Hall effect (AHE) in a polycrystalline Co2FeAl Heusler compound using combined experimental and theoretical studies. The Rietveld analysis of high-resolution synchrotron x-ray diffraction data reveals a large degree (~50 %) of antisite disorder between Fe and Al atoms. The analysis of anomalous transport data provides the experimental anomalous Hall conductivity (AHC) about 227 S/cm at 2 K with an intrinsic contribution of 155 S/cm, which has nearly constant variation with temperature. The detailed scaling analysis of anomalous Hall resistivity suggests that the AHE in Co2FeAl is governed by the Berry phase driven intrinsic mechanism. Our theoretical calculations reveal that the disorder present in Co2FeAl compound enhances the Berry curvature induced intrinsic AHC.

cond-mat.mtrl-sci↗

arXiv2021

Anomalous Hall effect from gapped nodal line in Co2FeGe Heusler compound

Full Heusler compounds with Cobalt as a primary element show anomalous transport properties owing to the Weyl fermions and broken time-reversal symmetry. We present here the study of anomalous Hall effect (AHE) in Co2FeGe Heusler compound. The experiment reveals anomalous Hall conductivity (AHC) 100 S/cm at room temperature with an intrinsic contribution of 78 S/cm . The analysis of anomalous Hall resistivity suggests the scattering independent intrinsic mechanism dominates the overall behaviour of anomalous Hall resistivity. The first principles calculation reveals that the Berry curvature originated by gapped nodal line near EF is the main source of AHE in Co2FeGe Heusler compound. The theoretically calculated AHC is in agreement with the experiment.

cond-mat.mtrl-sci↗