Faculty Publications
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Item Ferromagnetism in Mn-Doped ZnO: A Joint Theoretical and Experimental Study(American Chemical Society, 2021) Ali, N.; Singh, B.; A R, V.; Lal, S.; Yadav, C.S.; Tarafder, K.; Ghosh, S.We present a joint theoretical and experimental investigation on the origin of ferromagnetism in Mn-doped ZnO. Theoretical calculations revealed that the zinc vacancy (VZn) induces ferromagnetic ordering (FMO), whereas the oxygen vacancy (VO) quenches FMO in the Mn-doped ZnO system. This is further corroborated by the experimental results. Magnetic measurements revealed that Mn-doped ZnO shows room-temperature ferromagnetism (RTFM). Saturated magnetic moment per Mn2+ ion increases with oxygen partial pressure, indicating that the VZn enhances FMO in Mn-doped ZnO. Electron paramagnetic resonance and photoluminescence measurements revealed the presence of VZn in Mn-doped ZnO films. X-ray photoelectron spectroscopy measurements showed mixed oxidation states of Mn in Mn-doped ZnO films. Finally, we show that RTFM at very low doping concentrations is due to the overlapping of bound magnetic polarons. However, due to antiferromagnetic coupling at higher doping concentrations, the FMO weakens. © 2021 American Chemical Society.Item Phonon dynamics with collective spin excitations and orbital ordering in quasi-two-dimensional La1.4Sr1.6Mn2 O7(American Physical Society, 2025) Mekap, S.; Kumar, B.; Ananthram, K.S.; Tarafder, K.; Ghosh, S.; Roy, A.This paper discusses the coupling between spin-wave-mediated magnetic interactions and lattice degrees of freedom in bilayer La1.4Sr1.6Mn2O7 (BL-LSMO-0.3). The thermal evolution of the Raman shift, as obtained from micro-Raman spectroscopic measurements over a wide temperature range, reveals the evolution of phonon dynamics while the system undergoes a balance between double and superexchange spin-spin interactions through spin-wave modulation in different magnetic phases. The evolution of relative magnetoelastic coupling strengths for nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic superexchange interactions in the high-temperature canted antiferromagnetic phases are estimated. We have also demonstrated the existence of orbital ordering and its correlation with spin-phonon dynamics in the canted antiferromagnetic phases of BL-LSMO-0.3 from the detailed analysis of the high-wave-number orbiton-related phonon modes. Our study further reveals the absence of charge ordering in the compound. The complex coupling of lattice distortion, orbital ordering, the nearest- and next-nearest-neighbor spin-spin interactions in determining the canted spin states of the system is discussed. © 2025 American Physical Society.