Influence of the RE2O3 (RE = Y,Gd) and CaO nanoadditives on the electromagnetic properties of nanocrystalline Co0.2Ni0.3Zn0.5Fe2O4

The present work reports the influence of the nanoadditives Y₂O₃, Gd₂O₃, and CaO on the magnetic, electrical and dielectric properties of sintered nanoferrites Co_0.2Ni_0.3Zn_0.5Fe₂O₄. All powders were synthesized via the polyol method. XRD analysis showed that except the nanoferrite which was obtained by in an one-post procedure, subsequent calcinations of the as-produced additives were necessary to obtain nanocrystals of the desired phases. The mean particle size inferred from TEM images of the nanoadditives sintered at 1000 °C ranges from 87 nm for Y₂O₃ to 126 nm for CaO. IR spectroscopy provided useful information on the nature of the core and the surface chemistry of the as-produced additives and their associated annealed powders. Upon sintering, it was found that the incorporation of 5 wt.% additives remarkably increased the densification of the doped materials. The most important increase in densification was observed with CaO due to its larger particles. dc M-H hysteresis loops taken at 300 K revealed a superparamagnetic behavior of the produced ferrite/nanoadditives. Additionally, as expected, the ferrite/nanoadditives showed reasonable saturation magnetization and high Curie temperature. The electrical and dielectric properties, namely the resistivity, the loss factor, and the relation frequency were found to be clearly affected by doping. The resistivity decreased with increasing temperature indicating a semiconducting behavior. Further, at room temperature, the highest resistivity was observed with Y₂O₃. The major role was attributed to the high fraction of insulating Y₂O₃ owing to its smallest particles combined with the low Fe²⁺ concentration in the ferrite nanoparticles taking advantages of the moderate sintering temperature. In addition, the dc conductivity was found to follow the Arrhenius law with a slope change observed at the Curie temperature. Further, all the additives clearly affected the ac conductivities of the pure ferrite. The variation of the dielectric permittivity with frequency and temperature was explained on the basis of M-W type of interfacial polarization. Additionally, at high frequencies, the lower dielectric loss was found with Y₂O₃ doping. It was found to be of about 10 times lower than the undoped material and much larger than reported for similar undoped bulk ferrites.