Effect of Cr Substitution for Co on the Structural, Optical, and Magnetic Properties of La₂CoMnO₆ Double Perovskite Nanomaterials: A Facile Auto-Combustion Sol-Gel Approach

The structural, optical, electronic, and magnetic properties of La 2 Co (1−x) Cr (x) MnO 6 (0 ≤ x ≤ 1) double perovskites synthesized via the sol-gel auto-combustion method were systematically investigated. X-ray diffraction confirmed the formation of a single-phase monoclinic structure ( P 2 1 /n space group) in all samples, with crystallite sizes decreasing as Cr content increased, as determined by the Debye–Scherrer formula. FESEM revealed an irregular chip-like morphology and a reduction in grain size with increasing Cr content at the Co site. The optical bandgap, calculated using the Tauc relation, exhibited a nonlinear dependence on Cr composition, suggesting a bandgap bowing effect. FTIR spectrum revealed a shift in La–O–La bending vibrations from 595 cm −1 (x = 0) to 618 cm −1 (x = 1) with increasing Cr incorporation. XPS analysis confirmed the presence of Cr 3+ , Mn 3+ , Mn 4+ , Co 2+ , and Co 3+ ions, validating the oxidation states of the constituent elements. Magnetic measurements indicated a significant reduction in Curie temperature (T C ), coercive field (H C ), and remanence (M r ) with increasing Cr doping, attributed to mixed valence state and ionic radius mismatches among Co, Mn, and Cr. This study, emphasizing the magnetic, optical, and electronic properties of Cr-substituted La 2 CoMnO 6 , highlights its potential for advanced applications in spintronic and photovoltaic devices.