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Bandgap Engineering and Signature of Ferromagnetism in Ti 1− x Mn x O 2 Diluted Magnetic Semiconductor Nanoparticles: A Valence Band Study
Author(s) -
Prajapati Brijmohan,
Roy Somnath,
Sharma Subhash,
Joshi Amish G.,
Chatterjee S.,
Ghosh Anup K.
Publication year - 2019
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201800262
Subject(s) - magnetic semiconductor , x ray photoelectron spectroscopy , materials science , valence (chemistry) , band gap , analytical chemistry (journal) , raman spectroscopy , doping , photoluminescence , polaron , ferromagnetism , spectroscopy , condensed matter physics , chemistry , nuclear magnetic resonance , electron , physics , optoelectronics , chromatography , quantum mechanics , optics , organic chemistry
Diluted magnetic semiconductor Ti 1− x Mn x O 2 (0.0 ≤ x ≤ 0.06) nanoparticles have been synthesized by sol–gel technique. Phase purity, structural, micro‐structural, and vibrational properties of the samples have been studied by X‐ray diffraction, transmission electron microscopy (TEM), high‐resolution TEM, and Raman spectroscopy. UV–Vis and photoluminescence spectroscopy clearly indicate the tuning of bandgap and appearance of different defect states (oxygen vacancies) with Mn‐doping, respectively. Chemical states and surface stoichiometry of the samples have been probed by X‐ray photoemission spectroscopy (XPS). Shifting of binding energy of Ti2p toward lower value and appearance of Mn 2+ , Mn 3+ , and Mn 4+ confirm Mn doping into TiO 2 and also indicate that Mn‐doping reduces the number of oxygen vacancies in the system. Valence band studies have been done by XPS and ultraviolet photoemission spectroscopy (UPS) valence band spectra. Combined result of valence band spectra and optical data reveals shortening of HOMO–LUMO gap with increasing Mn‐concentration. Room temperature ferromagnetism, originating from oxygen vacancies, has been explained on the basis of the bound magnetic polaron (BMP) model. Resistivity measurements have been conducted to examine the semiconducting behavior and to study the electrical conduction mechanism. It is revealed that the thermally activated conduction (Arrhenius) mechanism is valid in the high temperature region whereas Mott's variable‐range hopping (VRH) mechanism is applicable in low temperature region.