Complex permeability and optical studies of Cr+3 doped nano-structured γ-Fe2O3 synthesized by auto-combustion technique

• Significant enhancement in permeability after Cr3+ doping.
• Real permeability shows unusual behaviour.
• Permeability is highest at all temperature and frequencies for x = 0.07.
• Material has dual band gap structure falling within the solar energy spectrum.

We have successfully synthesized chromium doped gamma ferrite (γ-Fe2O3) nanopowders (16.9 nm to 25.6 nm) of the composition (Fe2−xCrxO3 for x = 0.00, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10) by a slightly modified solution combustion method using citric acid as fuel at considerably low temperature. The so prepared powders were extensively studied for complex permeability and optical behaviour. It was found that Cr3+ doped γ-Fe2O3 has significant permeability values and it can therefore be used as a high permeability core material and in Multi-layer Chip Inductor (MLCI) applications in electronic products, such as cellular phones, computers and video cameras. The results obtained in terms of permeability spectra suggest that γ-Fe2O3 and its doped variants when made in nano-form behave as a high permeability material at ultra high frequencies (5–25 MHz) with permeability showing unusual inverse dependence on the grain dimension. Optical studies of the material confirm the presence of two band gaps BGd1 and BGd2 falling within the solar energy spectrum, thereby making this material a promising candidate for single junction photovoltaics with enhanced power conversion efficiency. We have also shown that the nano-sized γ-Fe2O3 synthesized by cost effective and modified sol–gel auto-combustion technique can be a good alternative to highly mismatched alloys (HMAs).