Controlled Preparation And Microwave Electromagnetic Properties Of The Nickel-based Spinel Ferrite Nanofibers

In this work, Ni_1-xZn_xFe₂O₄, Ni_0.3Cu_0.2Zn_0.5Fe₂O₄and (Ni_0.5Zn_0.5Fe₂O₄)1–x（SiO₂）_xnanofibers were fabricated by electrospinning and subsequent calcination process. Theirstructural, morphological, magnetostatic, electromagnetic and microwave absorptionproperties were characterized, and the relationship between structure, composition andproperties was investigated.For the Ni_0.5Zn_0.5Fe₂O₄nanofibers, the average grain size gradually increases and thesurface morphology changes from cylinder-like to chain-like structure with the increase ofcalcination temperature. Meanwhile the specific saturation magnetization increasesmonotonously while the corresponding coercivity shows a trend of first increase and thendecrease. The microwave absorbing capability of Ni_0.5Zn_0.5Fe₂O₄nanofibers is enhancedwith increasing calcination temperature. The reflection loss peak value decreases and theeffective absorbing bandwidth corresponding to the reflection loss below–10dB increases.When the absorber thickness is5mm, a minimum reflection loss value of–47.62dB isachieved for the synthesized Ni_0.5Zn_0.5Fe₂O₄nanofibers calcined at1000℃, and thecorresponding effective absorbing bandwidth reaches8.8GHz. With increasing the filler(i.e., Ni_0.5Zn_0.5Fe₂O₄nanofibers) content, the microwave absorbing intensity as well as thebandwidth increase, and the reflection loss peak shifts to low frequency. Additionally, it isfound that the fiber diameter have no obvious influence on the microwave absorptionperformance of Ni_0.5Zn_0.5Fe₂O₄nanofibers.With the increase of Zn/Ni ratio or Zn content, the lattice constant and the averagegrain size of Ni_1-xZn_xFe₂O₄nanofibers progressively increase. Also, the coercivity generallyshows a downward trend, whereas the specific saturation magnetization increases initially,reaching a maximum value for the sample with x=0.4, and then decreases with furtherincrease in Zn content. The peak value of the microwave reflection loss initially decreasesand then increases with increasing Zn content, but the peak frequency has no obviouschange. The sample with x=0.5has a minimum reflection loss at the same filler contentand thickness.The doping of SiO₂or Cu gives rise to the notably influences on the structure andcharacteristics of Ni_0.5Zn_0.5Fe₂O₄nanofibers. The introduction SiO₂leads to a reduction inaverage size of Ni_0.5Zn_0.5Fe₂O₄grains contained in composite nanofibers, which in turnresults in a monotonous decrease in the specific saturation magnetization and a tendency offirst increase and then decrease in the coercivity. With the increase of SiO₂dosage, the magnetic loss of (Ni_0.5Zn_0.5Fe₂O₄)1–x（SiO₂）_xcomposite nanofibers substantially decreases inthe low frequency range but the dielectric loss has a certain increase over the wholefrequency range （i.e.,2–18GHz）. As a result, the microwave absorbing peak decreasesconsiderably in the low frequency range （i.e., C-band） but the one increases slightly in thehigh frequency range （i.e., Ku-band）. The partial substitution of Cu for Ni is found toincrease the grain size, specific saturation magnetization, magnetic loss in the lowfrequency range and absorption properties. The minimum reflection loss of the coatingcontaining Ni_0.3Cu_0.2Zn_0.5Fe₂O₄nanofibers calcined at700℃as filler reaches–40.97dBwith a thickness of6mm, this is about36%lower than that of the coating based onNi_0.5Zn_0.5Fe₂O₄nanofibers at same conditions.