Structural, magnetic and dielectric properties of spinel MgFe₂O₄ by sol–gel route

Importance of spinel ferrites arises due to their technological and industrial applications in electronic and spintronic devices. Among magnetic ferrites with formula XFe₂O₄ (where X = Co, Ni, etc.), magnesium ferrite, with unique magnetic properties along with n-type conductivity, has significant advantage over other spinel ferrites. In this work MgFe₂O₄ sols and thin films are prepared using sol–gel and spin coating method. Mg/Fe ratio is varied as 0.4, 0.45, 0.5, 0.55, 0.6. Magnetic properties of sols indicate presence of single magnetic phase with Mg/Fe ratio of 0.55. Variation in Mg/Fe ratio during sol synthesis not only affects the magnetic properties but also affects phase purity of magnesium iron oxide thin films. Presence of diffraction peaks corresponding to (220), (222), (400), (331) and (620) planes confirm the formation of MgFe₂O₄ at low annealing temperature of 300 °C with Mg/Fe ratio of 0.55. This is the lowest temperature that has ever been reported for the formation of phase pure MgFe₂O₄ thin films. Phase purity at Mg/Fe ratio of 0.55 also results in high dielectric constant and low dielectric loss. Arrhenius plot for conductivity shows semiconducting behavior due to electron hopping between Fe²⁺ and Fe³⁺ cations. Moreover, strong magnetic behavior with high saturation magnetization of 163 emu/cm³ is obtained with Mg/Fe ratio of 0.55. Saturation magnetization decrease with Mg/Fe 0.4, 0.45, 0.5 and 0.6.