Influence of doping on magnetic and electromagnetic properties of spinel ferrites
Abanti Nag, Rapaka S. Chandra Bose, A. ManojKumar, K. S. Venu, Hema Singh
Abstract
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.