Browsing by Author "A.M. Awasthi"

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Hidden transition in multiferroic and magnetodielectric CuCrO2 evidenced by ac-susceptibility
(Institute of Physics Publishing, 2017) Kaushak K. Shukla; Arkadeb Pal; Abhishek Singh; Rahul Singh; J. Saha; A.K. Sinha; A.K. Ghosh; S. Patnaik; A.M. Awasthi; Sandip Chatterjee
Ferroelectric polarization, magnetic-field dependence of the dielectric constant and ac and dc magnetizations of frustrated CuCrO2 have been measured. A new spin freezing transition below 32 K is observed which is thermally driven. The nature of the spin freezing is to be a single-ion process. Dilution by the replacements of Cr ions by magnetic Mn ions showed suppression of the spin freezing transition suggesting it to be fundamentally a single-ion freezing process. The observed freezing, which is seemingly associated to geometrical spin frustration, represents a novel form of magnetic glassy behavior. © CopyrightEPLA, 2017.
Phase diagram and electronic structure of Ni2+x Mn1-x Ga
(2006) S. Banik; Aparna Chakrabarti; U. Kumar; P.K. Mukhopadhyay; A.M. Awasthi; R. Ranjan; J. Schneider; B.L. Ahuja; S.R. Barman
We determine the phase diagram of Ni2+x Mn1-x Ga as a function of x (00.2 has been identified. The structure of this phase is found to be tetragonal from high-temperature x-ray-diffraction (XRD) studies. XRD, magnetization, and DSC measurements show that the paramagnetic tetragonal phase evolves from the lower temperature ferromagnetic tetragonal phase through a second-order phase transition without any change of structure. The unoccupied conduction band has been studied by inverse photoemission spectroscopy. It is dominated by Mn 3d -like states, and is in good agreement with FPLAPW based calculations. © 2006 The American Physical Society.
Structural studies of Ni2+x Mn1-x Ga by powder x-ray diffraction and total energy calculations
(2007) S. Banik; R. Ranjan; A. Chakrabarti; S. Bhardwaj; N.P. Lalla; A.M. Awasthi; V. Sathe; D.M. Phase; P.K. Mukhopadhyay; D. Pandey; S.R. Barman
The crystal structure of Ni2+x Mn1-x Ga has been studied as a function of composition (x) by powder x-ray diffraction. For Ni2.24 Mn0.75 Ga, where one-fourth of the Mn atoms are replaced by Ni, the experimentally determined lattice constants are in good agreement with theoretical equilibrium lattice constants calculated by minimization of total energy using full potential linearized augmented plane-wave method. For 0.15≤x≤0.35, a nonmodulated tetragonal martensitic phase is obtained at room temperature, whose lattice constant c increases and a decreases linearly with increasing x following Vegard's law. A 7M modulated monoclinic phase is obtained for x=0.2 due to annealing. The small width of the hysteresis of the martensitic transition shows its thermoelastic nature that is the characteristic of a shape memory alloy. Phase coexistence is observed for 0.1≤x≤0.15 at room temperature, confirming the first-order nature of the martensitic transition. © 2007 The American Physical Society.