Co–Mn Ferrite Thin Films Deposited by Spray Pyrolysis: Role of Annealing Temperature in Modulating Structural, Optical, and Electrical Properties

The promising properties of spinel ferrite for various applications must be completed by the development of flexible and inexpensive thin film deposition processes. In this work, Co–Mn spinel ferrite thin films (Co_0.33Mn_0.33Fe_2.33O₄) were successfully deposited on quartz and silicon substrates using a low-cost spray pyrolysis technique. The films were annealed at 700°C and 900°C to investigate the effect of thermal treatment on their structural, optical, and electrical properties. X-ray diffraction confirmed the formation of a single-phase cubic spinel structure with improved crystallinity and increased crystallite size at higher temperatures. Scanning electronic microscopy and energy dispersive of X-ray photons analyses showed uniform morphology and homogeneous elemental distribution, demonstrating high-quality and defect-controlled films. Optical studies revealed a progressive band gap reduction from 2.08 to 1.81 eV with increasing annealing temperature, attributed to grain growth and reduced defect density, favoring enhanced visible light absorption. Electrical characterization of the Ag/ferrite/n-Si heterostructures exhibited rectifying behavior, with I–V and C–V measurements at 900°C suggesting a double-diode configuration and enhanced carrier mobility. Frequency-dependent conductance transitioned from a single Jonscher power law to a double-slope behavior upon annealing, consistent with reduced defect density and modified hopping mechanisms. These results demonstrate that spray pyrolysis is an effective route for producing high-quality Co–Mn ferrite thin films and highlight the crucial role of annealing temperature in tuning their structural and functional properties. Such films have promising potential for integration into microwave, magnetic, and photovoltaic devices.