Mössbauer and optical investigation of Co3−x Fe x O4 thin films grown by sol–gel process

Structural transformation and the related variation in magnetic and optical properties of Co_3?x Fe _x O₄ thin films grown by a sol–gel method have been investigated as the Fe composition varies up to x?=?2. The normal spinel phase is dominant below x?=?0.55 and the inverse spinel phase grows as x increases further. Conversion electron Mössbauer spectroscopy (CEMS) measurements indicate that the normal spinel phase have octahedral Fe³⁺ ions mostly while the inverse spinel phase contain octahedral Fe²⁺ and tetrahedral Fe³⁺ ions. For higher Fe composition (x?>?1.22), Co²⁺ ions are found to substitute the octahedral Fe²⁺ sites. The measured optical absorption spectra for the Co_3?x Fe _x O₄ films by spectroscopic ellipsometry support the CEMS interpretation.