Browsing by Author "Ajit K. Jena"

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Atomic disorder and Berry phase driven anomalous Hall effect in a Co2FeAl Heusler compound
(American Physical Society, 2022) Gaurav K. Shukla; Ajit K. Jena; Nisha Shahi; K.K. Dubey; Indu Rajput; Sonali Baral; Kavita Yadav; K. Mukherjee; Archana Lakhani; Karel Carva; Seung-Cheol Lee; Satadeep Bhattacharjee; Sanjay Singh
Co2-based Heusler compounds are promising materials for spintronics applications due to their high Curie temperature, large spin polarization, large magnetization density, and exotic transport properties. In the present paper, 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 the Co2FeAl compound enhances the Berry curvature induced intrinsic AHC. © 2022 American Physical Society.
Atomic disorder and intrinsic anomalous Hall effect in a half-metallic ferromagnet Co2VAl
(Elsevier Ltd, 2025) Shivani Rastogi; Vishal Kumar; Ajit K. Jena; Nisha Shahi; Gaurav K Shukla; Sunil Wilfred D'Souza; Satadeep Bhattacharjee; Sanjay Singh
Half-metallic ferromagnets, conducting for one spin channel while insulating for the other, are highly desirable for spintronic applications due to 100 % spin polarization around the Fermi level. Cobalt-based half-metallic Heusler compounds have attracted enormous attention due to their large spin polarization and a high magnetic transition temperature. In the present study, we report the experimental and theoretical investigation of crystal structure and anomalous Hall effect (AHE) in half-metallic ferromagnet Co2VAl. The structural investigation of high-resolution synchrotron x-ray diffraction data reveals 10 % antisite disorder between V and Al atoms within the L21 ordered crystal structure. The scaling analysis of anomalous Hall data shows that the AHE in our system is mainly driven by the Berry curvature in the momentum space. The magnitude of experimental intrinsic anomalous Hall conductivity (AHC) due to the momentum space Berry curvature is about 44.67 ± 0.02 S/cm at 5 K, which is less than the theoretically calculated AHC for the ordered structure. Our theoretical calculations suggest that the lower AHC obtained for the present system is due to the reduced Berry curvature in the disordered case with negligible impact on half-metallicity of the system. © 2024 Elsevier B.V.
Pressure driven iso-structural phase transition and its implication on the Néel skyrmion host hexagonal PtMnGa
(American Physical Society, 2024) K.K. Dubey; S. Rastogi; Ajit K. Jena; Gaurav K. Shukla; Parul Devi; Seung-Cheol Lee; Satadeep Bhattacharjee; R. Rawat; Boby Joseph; Sanjay Singh
Magnetic skyrmions are nanometer-sized whirling spin textures in the magnetic material, which have the potential to revolutionize the field of spintronics. This study explores the influence of pressure on the structural properties of the PtMnGa hexagonal system, recognized for hosting Néel skyrmions. By employing pressure-dependent synchrotron x-ray powder diffraction (SXRPD), we reveal an isostructural phase transition in this system at approximately 6 GPa. The isostructural transition is evidenced by a deviation of the lattice parameter from the linear dependence, change of trend in the in-plane to out-of-plane lattice parameter ratio, and a description of the pressure-unit cell volume data by two distinct second-order Birch-Muraghan equation of states. The PtMnGa system, however, exhibits reversible structural behavior when pressure is released. Analysis of combined pressure and temperature-dependent SXRPD data provides indirect evidence that the application of moderate pressure (0.8-1.09 GPa) shifts the thermodynamically stable skyrmion regime near to room temperature in the Néel skyrmion-host PtMnGa system. Theoretical calculations on band structure, magnetic moment, and density of states (DOS) under pressure further corroborate the experimental findings, offering a comprehensive understanding of the material's response to pressure changes. The combination of experimental findings and theoretical calculations demonstrates the potential for engineering materials supporting stable skyrmions even at elevated temperatures and nominal pressures, which can be attained in the materials using chemical substitution or epitaxial thin films by strain controlling of the substrate-film lattice parameter mismatch. © 2024 American Physical Society.
Role of chemical disorder in tuning the Weyl points in vanadium doped Co2TiSn
(American Physical Society, 2021) Payal Chaudhary; Krishna Kant Dubey; Gaurav K. Shukla; Sanjay Singh; Surasree Sadhukhan; Sudipta Kanungo; Ajit K. Jena; S.-C. Lee; S. Bhattacharjee; Jan Minár; Sunil Wilfred D'Souza
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 Co2Ti1-xVxSn 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 Co2TiSn 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 Co2TiSn will be an ideal composition for the experimental investigation of Weyl physics. © 2021 American Physical Society.
Tuning of nodal line states via chemical alloying in Co2 CrX (X=Ga, Ge) Heusler compounds for a large anomalous Hall effect
(American Physical Society, 2024) Ujjawal Modanwal; Gaurav K. Shukla; Ajit K. Jena; Satadeep Bhattacharjee; Sunil Wilfred D'Souza; Jan Minár; Sanjay Singh
Topological materials have attracted significant interest in condensed matter physics for their unique topological properties leading to potential technological applications. Topological nodal line semimetals, a subclass of topological materials, exhibit symmetry-protected nodal lines, where band crossings occur along closed curves in the three-dimensional Brillouin zone. When the nodal lines are gapped out due to perturbation in the Hamiltonian, a large Berry curvature (BC) arises in the surrounding area of the gapped nodal line, leading to exotic anomalous transport responses. In this paper, we studied the Co2CrX (X=Ga, Ge) Heusler compounds that exhibit mirror symmetry-protected nodal line states below the Fermi level. The BC calculation yields anomalous Hall conductivity (AHC) of about 292 and 217 S/cm for Co2CrX (X=Ga, Ge), respectively, at the Fermi level, which increases by up to 400% at the nodal line energy level. We theoretically analyzed that 20% and 60% zinc (Zn) alloying in Co2CrX (X=Ga, Ge) effectively lowers the Fermi level by 50 meV and 330 meV, respectively, aligning with the protected crossings. Consequently, we identified Co2CrGe0.4Zn0.6 and Co2CrGa0.8Zn0.2 as compositions to achieve the significant AHC of 800 and 1300 S/cm, respectively. The explicit AHC calculation for these alloyed compositions is in good agreement with our predictions. Our findings highlight that chemical alloying is an efficient way to enhance AHC in nodal line hosting materials. © 2024 American Physical Society.