Study on Structural and Optical Properties of Nanocrystalline Mn–Ni Ferrites Prepared by Auto-Combustion Technique
Nanocrystalline mixed ferrites with the general formula MnxNi1-xFe2O4(x = 0.0 to 1.0, in steps of 0.2) were successfully synthesized using the auto-combustion technique. The main objective of this work was to investigate the effect of Mn substitution at Ni sites on the structural and optical properties of NiFe2O4 in the nanocrystalline regime. X-ray diffraction (XRD) reflections were consistent with the formation of a cubic spinel structure for all compositions. No additional crystalline impurity peaks were detected within the sensitivity of conventional powder XRD. The average crystallite size estimated from the Scherrer equation lies in the range of 26–33 nm, confirming the nanocrystalline nature of the synthesized powders. The slight variation in crystallite size with increasing Mn content suggests that ionic substitution influences the growth kinetics during combustion synthesis. Ultraviolet–visible (UV–Vis.) diffuse reflectance spectroscopy was used to study the optical response, and the apparent optical bandgap values were estimated from UV–Vis. absorbance data using Tauc analysis. The bandgap varies from 1.18 to 1.58 eV, revealing clear composition-dependent optical tuning. These results show that Mn substitution effectively changes the electronic structure and optical response, making MnxNi1-xFe2O4 ferrites favorable materials for optoelectronic and photocatalytic applications. Received: 29 January 2026 | Revised: 20 May 2026 | Accepted: 26 June 2026 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study. Author Contribution Statement Laxmi J. Hathiya: Conceptualization, Methodology, Software, Formal analysis, Investigation, Data curation, Writing – original draft, Visualization. Hiren H. Joshi: Validation, Resources, Writing – review & editing, Supervision, Project administration.