Faculty Publications

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    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.
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    Magnetic complexity, magnetodielectric effect and DFT calculations on correlation driven Gd2CoMnO6 insulator
    (Elsevier B.V., 2022) Prashanth, C.H.; Reddy, I.; Tarafder, K.; Chandrasekhar Kakarla, D.; Yang, H.D.; Adyam, V.; Jyothinagaram, K.
    In the family of Re2CoMnO6 manganite double perovskites, in contrast to parent La2CoMnO6 compound, Gd2CoMnO6 exhibits multiple magnetic transitions; ferromagnetic (FM) ordering, TC ∼ 112 K followed by AFM transition, TN ∼ 47 K, Gd spins ordering for T < 10 K and large isothermal entropy changes. A study of DC field-superimposed AC magnetic susceptibility measurements revealed the field-induced magnetic glassy behavior below TC and enhancement of FM correlations above TC. From the analysis of Almeida-Thouless behavior and dynamical power-law fit to frequency dependent AC susceptibility, Gd2CoMnO6 exhibits a volume spin glass-like nature below the freezing temperature, Tf ∼ 117.5 K. The isothermal field-dependent magnetic and dielectric permittivity data and temperature dependent Raman measurements (reported in ref. R. X. Silva et al., J, Appl. Phys. 114 194,102 (2013)) confirms the spin-phonon coupling induced magnetodielectric effect. Further, the ground-state electronic structure and magnetic properties of Gd2CoMnO6 are investigated using DFT + U formalism with Vienna Ab-initio Simulation Package (VASP) code and predicted the material to be a correlation-driven insulator. The correlation value of the Hubbard U parameter at the 4f-Gd elements changes the stability of the magnetic state from Ferri to FM spin alignment for Ueff ≥ 3 eV and is correlated to the experimentally observed field-induced transformation of the short-range-order FiM/spin-glass-like phase into the long-range ordered FM phase. © 2022