Role of phase transition in the dielectric and magnetic properties of Na containing NiO. (July 2019)

• Record Type: Journal Article
• Authors: Joshi, D.C.; Pramanik, P.; Warshi, M.K.; Ghosh, S.; Meher, A.; Dasari, K.; Thota, S.
• Is Part Of: Journal of physics and chemistry of solids. Volume 130(2019)
• Page Start: 154
• Page End: 164
• Publication Date: 2019-07
• Subjects: Solids -- Periodicals; Solides -- Périodiques; Solids; Periodicals; 530.41
• DOI: 10.1016/j.jpcs.2019.02.012
• Languages: English
• ISSNs: 0022-3697

Abstract

Abstract: In this study, we systematically investigated the phase transition (cubic (90°) → rhombohedral (60.01°)) and its role in the electronic structure, dielectric, and magnetic behavior of Ni1− x Na x O (0.02 ≤ x ≤ 0.2). X-ray photoelectron spectroscopy indicated non-local screening of the divalent Ni by oxygen and monovalent sodium ions together with giant multiplet splitting. At 310 K, the longitudinal optical phonon mode (500 cm −1 ) dominated over all the vibrational excitations, but for the dilute dispersion of Na, the transverse optical phonon mode (455 cm −1 ) exhibited the highest intensity among all the modes. Even at a very low level ( x ∼ 0.02) of Na substitution, the intensity of the 2-magnon mode (1530 cm −1 ) was significantly suppressed. The onset of the structural transition and antiferromagnetic Néel temperature (TN ) shifted to a high temperature region with moderate Na substitution, which has significant implications for the dependence of the relative dielectric permittivity (εR (T)) and magnetic susceptibility ( χ mag (T)) on the temperature. The dependence of the ac-resistivity ρ ac (T, f ) on the temperature and frequency followed Mott's variable range-hopping mechanism for charge carriers between the localized states, where the activation energies were highly dependent on the spin (S = 1/2) of the type-II antiferromagnetic system. The magnetization isotherms (M–H) were analyzed using a modified Langevin function M = M o L ( μ P H k B T ) + χ a H and we extracted TN for the Ni1− x Na x O system. Highlights: Role of phase transition (cubic (90°)→Rhombohedral (60.01°)) on the edielectric and magnetic behavior of Ni1- x Na x O was reported. Longitudinal phonon and 2-Magnon modes dominates among all the modes, while the transverse phonon mode overtops for x ≤ 0.02. The onset of structural transition and TN shifts to high-T region which has significant implications on the dielectric behavior of Ni1- x Na x O. The ρ ac (T, f ) follows hopping of charge carriers between the localized states with EA depends on the spin of type-II AFM system. M-H isotherms are analyzed using modified Langevin function M = M o L ( μ p H k B T ) + χ a H and extracted TN for Ni1- x Na x O system.