Study of Phase Transition in Iron Oxide Thin Films

We here report preparation and characterization of iron oxide thin films using sol-gel method. Iron nitrate is used as precursor whereas water and ethylene glycol as solvent. Three different sols are prepared with pH 1 (Acidic), 7 (neutral) and 13 (basic). The films are spin coated on copper substrate and annealed at 300˚C for 60mins. XRD results indicate the formation of phase pure Fe3O4 at pH 1 while phase transition from Fe3O4 to γ-Fe2O3 is observed with change in pH from 1 to 7. Whereas in the basic medium (pH 13) α-Fe2O3 phase is obtained. These transitions between different phases of iron oxide strongly affect the magnetic properties. Films with pH 1 show highest saturation magnetization while decrease in saturation magnetization is observed as pH is increased to 7, indicative of phase transition from Fe3O4 to γ-Fe2O3. Further decrease in saturation magnetization in basic medium is associated with phase transition to α-Fe2O3 phase.