Influence of doping on magnetic and electromagnetic properties of spinel ferrites

In this study, spinel Ni 0.5 Zn 0.5 Fe 2 O 4 doped with transition metal ions as well as rare-earth ions Ni 0.4 Zn 0.4 M′ 0.2 Fe 2 O 4 (M′ = Cu, Dy, Gd and Lu) and M″ 0.5 Zn 0.5 Fe 2 O 4 (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- 3 m space group for all the compositions. Rietveld refinement confirms that doped Cu 2+ , Dy 3+ , Gd 3+ and Lu 3+ ions are at random distribution between spinel tetrahedral and spinel octahedral sites against their preferential occupancy. The saturation magnetisation ( M S ) of Ni 0.5 Zn 0.5 Fe 2 O 4 ( M S = 50.5 emu/g) increased with partial doping showing M S = 60.08 emu/g for transition-metal doped Ni 0.4 Zn 0.4 Cu 0.2 Fe 2 O 4 and M S = 109.7 emu/g for rare-earth doped Ni 0.4 Zn 0.4 Dy 0.2 Fe 2 O 4 , which was the highest among all the doped compositions. Doping enhances the dielectric permittivity of Ni 0.5 Zn 0.5 Fe 2 O 4 from 4.2 to 6.5 for Ni 0.4 Zn 0.4 Cu 0.2 Fe 2 O 4 and 7.7 for Ni 0.4 Zn 0.4 Dy 0.2 Fe 2 O 4 . Further, the reflection coefficient ( R L ) of all the doped compositions of Ni 0.4 Zn 0.4 M′ 0.2 Fe 2 O 4 (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 Ni 0.4 Zn 0.4 Cu 0.2 Fe 2 O 4 resulted in further improvement of its absorption characteristics of the incident EM waves with reflection coefficient ( R L ) 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.