Study On The Properties Of Ru-doped NiFe₂O₄ And Ni-Ru Co-doped SrFe₁₂O₁₉

In this paper,the influence of Ru ion doping on spinel ferrite NiFe₂O₄ and the influence of Ni-Ru co-doping on hexagonal ferrite SrFe₁₂O₁₉ were studied.The structure,magnetic properties and bsorption performance of these two ferrites were mainly analyzed.Got the following result:The NiFe_2-xRu_xO₄（x=0,0.1,0.3,0.5,0.7,0.9）compounds were synthesized by solid state reaction.The space group of NiFe_2-xRu_xO₄ is Fd-3m,which belongs to cubic crystal system.The FT-IR spectrum shows that Ru⁴⁺occupies both tetrahedral and octahedral positions.The ultraviolet absorption spectrum shows that the band gap of NiFe_2-xRu_xO₄ decreases from 1.57eV at x=0 to 1.44eV at x=0.9.Magnetic studies have found that the saturation magnetization decreases monotonically with increasing Ru⁴⁺doping concentration at T=300K,from 48.8669 emu/g at x=0 to 38.7845 emu/g at x=0.9.When T=2K,the saturation magnetization and coercive field of NiFe_2-xRu_xO₄ are larger than those at room temperature.All samples are saturated under a low magnetic field,and the coercivity is less than 40Oe,these characteristics confirm that NiFe_2-xRu_xO₄ has soft magnetic properties.The SrFe_12-2xNi_xRu_xO₁₉（x=0.1,0.3,0.5,0.7）compounds were synthesized by solid state reaction.During the experiment,the XRD fitting pattern shows that all samples are single-phase.Combined with FT-IR spectra analysis,it can be seen that Ni²⁺enters the octahedral（2a,4f2）position,Ru⁴⁺enters the tetrahedral（4f1）and bipyramid（2b）positions.We directly observed the grain morphology of all samples by scanning electron microscope and found that replacing Fe³⁺in SrFe_12-2xNi_xRu_xO₁₉ with Ni²⁺and Ru⁴⁺resulted in an increase in particle size.The ultraviolet absorption spectrum shows that the band gap gradually decreases with the doping of Ni²⁺and Ru⁴⁺.Magnetic studies have shown that the substitution of Ni-Ru leads to a reduction in coercive field and improved saturation magnetization.Regular lattice dislocation stripes are observed in high-resolution transmission electron microscopy images of x=0.5 and 0.7.The observed strong microwave absorption is mainly contributed by natural magnetic resonance,which is widened by local magnetic fields at dislocation stripes.At dislocation stripes,interface polarization also forms.Both the x=0.5 and 0.7samples are excellent single-layer microwave absorbers.In x=0.5,the bandwidth of reflection loss（RL）<-10dB is broader than 11.31 GHz of 6.69 GHz to>18 GHz.In x=0.7,an ultra-low RL=-82 dB is observed with a fairly wide bandwidth（RL<-10dB）of over 8.8 GHz in the range of 9.2 GHz to>18 GHz.As the thickness and the doping content vary,the absorption is able to cover the full range of 3.5-18 GHz.The excellent microwave absorption is based on the collaboration of good impedance matching and high attenuation factor.The quarter-wavelength criteria explain the relationship between the optimum thickness and the frequency.Compared to the advanced materials reported,both the absorption strength and the bandwidth of SrFe_12-2xNi_xRu_xO₁₉ are very competitive.