Heusler compounds, Magnetism, Spintronics, Magnetic Materials, Skyrmions
20
Scopus Publications
Scopus Publications
Noble Metal-Based High-Entropy Alloys for Energy Storage Applications Parul Devi High Entropy Materials for Energy Storage Devices, 2026 High-entropy alloys (HEAs) have evolved from mixing a small number of secondary constituents with the primary constituent used to confer desirable properties in materials. The enormous incorporation approach initially used for metals has been applied to the polymers, semiconductors, ionic, and low-dimensional substances. Among them, noble metal-based HEAs for energy storage applications are the most demanding choice for consumers seeking relatively low environmental impacts. This mixing of metals focuses on the shifts toward their multifunctional properties, such as mechanical, electrochemical, magnetic, electronic, caloric, hydrogen-related, and catalytic characteristics. This chapter focuses on the enormous compositional area that persists to be investigated, outlines the various abundant synthesis methods available, and extends to their utilization in thermal energy storage appliances, such as lithium-ion batteries, supercapacitors, and dielectric capacitors. In addition, we will shed light on different strategies to design the best material properties' storage devices with variable compositions and high impurity tolerance.
Pressure driven iso-structural phase transition and its implication on the Néel skyrmion host hexagonal PtMnGa K. K. Dubey, S. Rastogi, Ajit K. Jena, Gaurav K. Shukla, Parul Devi, Seung-Cheol Lee, Satadeep Bhattacharjee, R. Rawat, Boby Joseph, Sanjay Singh Physical Review Materials, 2024 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 N\'eel 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 N\'eel 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.
Simultaneous magnetic field and field gradient mapping of hexagonal MnNiGa by quantitative magnetic force microscopy Norbert H. Freitag, Christopher F. Reiche, Volker Neu, Parul Devi, Ulrich Burkhardt, Claudia Felser, Daniel Wolf, Axel Lubk, Bernd Büchner, Thomas Mühl Communications Physics, 2023 Magnetic force microscopy (MFM) is a scanning microscopy technique that is commonly employed to probe the sample’s magnetostatic stray fields via their interaction with a magnetic probe tip. In this work, a quantitative, single-pass MFM technique is presented that maps one magnetic stray-field component and its spatial derivative at the same time. This technique uses a special cantilever design and a special high-aspect-ratio magnetic interaction tip that approximates a monopole-like moment. Experimental details, such as the control scheme, the sensor design, which enables simultaneous force and force gradient measurements, as well as the potential and limits of the monopole description of the tip moment are thoroughly discussed. To demonstrate the merit of this technique for studying complex magnetic samples it is applied to the examination of polycrystalline MnNiGa bulk samples. In these experiments, the focus lies on mapping and analyzing the stray-field distribution of individual bubble-like magnetization patterns in a centrosymmetric [001] MnNiGa phase. The experimental data is compared to calculated and simulated stray-field distributions of 3D magnetization textures, and, furthermore, bubble dimensions including diameters are evaluated. The results indicate that the magnetic bubbles have a significant spatial extent in depth and a buried bubble top base.
Template-directed 2D nanopatterning of S = 1/2 molecular spins Kyungju Noh, Luciano Colazzo, Corina Urdaniz, Jaehyun Lee, Denis Krylov, Parul Devi, Andrin Doll, Andreas J. Heinrich, Christoph Wolf, Fabio Donati, Yujeong Bae Nanoscale Horizons, 2023 We demonstrate fabrication of a surface-supported array of VOPc with controlled spin-spin distance, electronic decoupling from the substrate, and individual addressability to realize molecular qubit platforms interfaceable to solid state devices.
Pressure-Induced Isostructural Phase Transition in Biskyrmion Host Hexagonal MnNiGa Anupam K. Singh, Parul Devi, Ajit K. Jena, Ujjawal Modanwal, Seung-Cheol Lee, Satadeep Bhattacharjee, Boby Joseph, Sanjay Singh Physica Status Solidi Rapid Research Letters, 2022 Magnetic skyrmions are vortex‐like spin textures, which can be manipulated by external stress or pressure via magnetoelastic effects. Herein, the observation of isostructural phase transition in a biskyrmion host hexagonal MnNiGa at pressure P ≈4 GPa using pressure‐dependent synchrotron X‐Ray powder diffraction (XRD) data analysis is presented. The XRD data reveals anisotropic compression behavior with pressure with different compression rates of the a‐axis in the basal plane and the c‐axis in the prismatic plane. However, the hexagonal symmetry remains unchanged for pressure up to 14 GPa. Fitting of unit cell volume with pressure using a second‐order Birch–Murnaghan equation of state reveals that the data fall into two distinct curves for those above and below 4 GPa. Herein, the understanding of crystal structure with the application of hydrostatic pressure in the biskyrmion host MnNiGa is contributed to, wherein the skyrmion textures can be manipulated by pressure due to their magnetoelastic character.
Electronic structures and optical characteristics of fluorescent pyrazinoquinoxaline assemblies and Au interfaces Soyeong Kwon, Dong Yeun Jeong, Weon-Sik Chae, Kyungju Noh, P. Devi, Luciano Colazzo, Youngmin You, Taeyoung Choi, Dong-Wook Kim Scientific Reports, 2021 Understanding the excitonic processes at the interfaces of fluorescent π-conjugated molecules and metal electrodes is important for both fundamental studies and emerging applications. Adsorption configurations of molecules on metal surfaces significantly affect the physical characteristics of junctions as well as molecules. Here, the electronic structures and optical properties of molecular assemblies/Au interfaces were investigated using scanning probe and photoluminescence microscopy techniques. Scanning tunneling microscopy images and tunneling conductance spectra suggested that the self-assembled molecules were physisorbed on the Au surface. Visible-range photoluminescence studies showed that Au thin films modified the emission spectra and reduced the lifetime of excitons. Surface potential maps, obtained by Kelvin probe force microscopy, could visualize electron transfer from the molecules to Au under illumination, which could explain the decreased lifetime of excitons at the molecule/Au interface.
Influence of Cr substitution on the reversibility of the magnetocaloric effect in Ni-Cr-Mn-In Heusler alloys C. Salazar-Mejía, P. Devi, S. Singh, C. Felser, J. Wosnitza Physical Review Materials, 2021 We present the effect of substitution-induced pressure on the reversibility of the magnetocaloric effect (MCE) in ${\mathrm{Ni}}_{2}{\mathrm{Cr}}_{x}{\mathrm{Mn}}_{1.4\ensuremath{-}x}{\mathrm{In}}_{0.6}$ ($x=0.1$, 0.2, 0.3) alloys, through characterization in pulsed magnetic fields. We measured the adiabatic temperature change $\mathrm{\ensuremath{\Delta}}{T}_{\text{ad}}$ directly during applied magnetic field pulses of 2 and 6 T. We paid special attention to the reversibility of $\mathrm{\ensuremath{\Delta}}{T}_{\text{ad}}$. The substitution of Mn by Cr in ${\mathrm{Ni}}_{2}{\mathrm{Mn}}_{1.4}{\mathrm{In}}_{0.6}$ leads to a negative pressure, as evidence by the increase of the lattice parameters, which shifts the martensitic transition towards lower temperatures and enhances the ferromagnetism of the martensite phase. We found a large value of $\mathrm{\ensuremath{\Delta}}{T}_{\text{ad}}=\ensuremath{-}7$ K at $T=270$ K for the sample with $x=0.1$ for a field change of 6 T. We discuss the reversibility of the MCE in these alloys in terms of the Clausius-Clapeyron equation.
