Influence of doping on magnetic and electromagnetic properties of spinel ferrites

Abstract

In this study, spinel Ni0.5Zn0.5Fe2O4 doped with transition metal ions as well as rare-earth ions Ni0.4Zn0.4M′0.2Fe2O4 (M′ = Cu, Dy, Gd and Lu) and M″0.5Zn0.5Fe2O4 (M″ = Ni, Mn and Co) are developed using the sol-gel auto-combustion route, and the role of substitution on electromagnetic properties is investigated. The powder X-ray diffraction accompanied by Rietveld refinement signifies a single-phase spinel ferrite that belongs to Fd-3m space group for all the compositions. Rietveld refinement confirms that doped Cu2+, Dy3+, Gd3+ and Lu3+ ions are at random distribution between spinel tetrahedral and spinel octahedral sites against their preferential occupancy. The saturation magnetisation (MS) of Ni0.5Zn0.5Fe2O4 (MS = 50.5 emu/g) increased with partial doping showing MS = 60.08 emu/g for transition-metal doped Ni0.4Zn0.4Cu0.2Fe2O4 and MS = 109.7 emu/g for rare-earth doped Ni0.4Zn0.4Dy0.2Fe2O4, which was the highest among all the doped compositions. Doping enhances the dielectric permittivity of Ni0.5Zn0.5Fe2O4 from 4.2 to 6.5 for Ni0.4Zn0.4Cu0.2Fe2O4 and 7.7 for Ni0.4Zn0.4Dy0.2Fe2O4. Further, the reflection coefficient (RL) of all the doped compositions of Ni0.4Zn0.4M′0.2Fe2O4 (M′ = Cu, Dy, Gd and Lu) was less than −8 dB (85% absorption) throughout the frequency band of 8–12 GHz with an optimum material thickness of 3.5 mm. Transition metal ion doped Ni0.4Zn0.4Cu0.2Fe2O4 resulted in further improvement of its absorption characteristics of the incident EM waves with reflection coefficient (RL) less than −10 dB (between 84.15% and 90%) between 10 and 12 GHz at a material thickness of 3.5 mm in the X-band frequency range.