arXiv subjects

Shashank Chaturvedi

Publications and source records attributed to Shashank Chaturvedi.

3 recordsLinked to original sources

arXiv2025

Magnetic transition in B2 Al-Cr-Co alloys

Using Density Functional Theory (DFT) calculations and Monte-Carlo (MC) simulations, we investigate the recently reported magnetic transition in B2 Al-Cr-Co alloys. The Cr sublattice is alloyed with different amounts of Co in the antiferromagnetic (AFM) B2 AlCr binary alloy and the resulting exchange interactions are analyzed within the Heisenberg Hamiltonian framework. DFT results reveal that at low Co concentrations the system favors the AFM order, while at high Co contents a transition to the ferromagnetic (FM) state is observed. Within the FM stability field, the Curie temperature (TC), obtained within the mean-field approximation, is below ~160 K and decreases with Co concentration. The calculated exchange parameters evolve systematically with Co content, and the trends are consistent with the DFT total energies. The magnetic configurations obtained from MC simulations follow the DFT results at low Cr levels but predict a spin-glass behavior for alloys containing more than 40 at.% Co on Cr sublattice. These findings provide a fundamental understanding of how the chemistry-driven changes in exchange interactions affect magnetism in the B2 Al-Cr-Co alloys.

cond-mat.mtrl-sci↗

arXiv2021

Raman and first-principles study of the pressure induced Mott-insulator to metal transition in bulk FePS$_3$

Recently discovered class of 2D materials based on transition metal phosphorous trichalcogenides exhibit antiferromagnetic ground state, with potential applications in spintronics. Amongst them, FePS$ _{3} $ is a Mott insulator with a band gap of $\sim$ 1.5 eV. This study using Raman spectroscopy along with first-principles density functional theoretical analysis examines the stability of its structure and electronic properties under pressure. Raman spectroscopy reveals two phase transitions at 4.6 GPa and 12 GPa marked by the changes in pressure coefficients of the mode frequencies and the number of symmetry allowed modes. FePS$_3$ transforms from the ambient monoclinic C2/m phase with a band gap of 1.54 eV to another monoclinic C2/m (band gap of 0.1 eV) phase at 4.6 GPa, followed by another transition at 12 GPa to the metallic trigonal P-31m phase. Our work complements recently reported high pressure X-ray diffraction studies.

cond-mat.mtrl-sci↗

arXiv2020

Tuning the structure of Skyrmion lattice system Cu2OSeO3 under pressure

The insulating ferrimagnet Cu2OSeO3 shows a rich variety of phases such as skyrmion lattice and helical magnetism controlled by interplay of different exchange interactions which can be tuned by external pressure. In this work we have investigated pressure-induced phase transitions at room temperature using synchrotron based x- ray diffraction and Raman scattering measurements. With first-principles theoretical analysis, we show that spin-spin exchange couplings in the ambient cubic phase are affected notably by hydrostatic pressure. The ambient cubic phase transforms to a monoclinic phase above 7 GPa and then to the triclinic phase above 11 GPa. Emergence of new phonon modes in the Raman spectra confirms these structural phase transitions. Notably, upon decompression, the crystal undergoes transition to a new monoclinic structure. Atomic coordinates have been refined in the low pressure cubic phase to capture the Cu-tetrahedra evolution responsible for the earlier reported magnetic behavior under pressure. Our experiments will motivate further studies of its emergent magnetic behavior under pressure.

cond-mat.mtrl-sci↗