Magnetism And Dielectric Relaxation Of Ni_0.5Zn_0.5Fe₂O₄ Ceramics

Ferrites are a batch of complex magnetic oxides of significant technological importance, which occur in several different crystal structure forms. Among them a remarkable structure is spinel which could be subdivided as conventional type (spinel) and inverted type. In general, ZnFe2O4 and NiFe2O4 fall within spinel (AB2O4 type) and inverted spinel type, respectively, so Nio.5Zno.5Fe2O4 (NZFO) is mixed spinel type. NZFO powders are important soft magnetic materials and widely applied in many fields such as ferrofluids, magnetic drug delivery, and magnetic high-density information storage. The bulks are also of excellent soft magnetism and of remarkable dielectric relaxation which may be used to be magnetic electronic components. In this paper, NZFO powders (calcining at various temperatures) and ceramics (sintering various temperatures) have been synthesized by co-precipitaion method, and their phase structure, surface morphology, dielectric properties and ferromagnetic properties are characterized.XRD patterns suggest that the as-prepared powders are spinel-typed and has a highly (311) orientation characterization. And the average grain sizes of the ZNFO nanoparticles range from 20.8 to 53.3 nm, as well as peaks of some samples shifting to lower angles due to lattice expansion. The activation energy is 30.83 kJ/mol which calculations from the derived XRD data. The magnetic properties measurements show that these samples are super-paramagnetic. And the saturation magnetization increases with annealing temperature, which may be explained by super-exchange interactions of Fe ions occurring at A-and B-sites. The variation of coercivity with particle size is interpreted on the basis of domain structure and crystal anisotropy. Furthermore, these nanoparticles exhibit a redshift phenomenon at lower temperatures being seen in the Raman spectra, which could be related to ionic substitution.The temperature dependence of dielectric permittivity of the NZFO ceramics has been investigated over a broad temperature range at selected frequencies (f=1,2,3,5, 10,20,30,50, and 100 kHz). For example, the NZFO ceramic sintered at 900℃, an extremely remarkable dielectric relaxation behavior was observed with its degree of relaxation△Tm-155 K, which was deciphered in detail by an effect between n-type and p-type carriers with temperature rising. By applying the Arrhenius equation to further study the relaxation mechanism, two activation energy values of～0.52 and 0.30 eV in different temperature regions were calculated, respectively. Furthermore, the various superparamagnetic saturation magnetizations of the NZFO samples sintered at different temperatures from the crystalline growth.In addition, the temperature dependence of dielectric permittivity of another ferrite BiFeO3 ceramics has been also investigated. Like NZFO ferrite, there is a remarkable dielectric relaxation observed, suggesting the dielectric relaxation may be a common phenomenon among ferrites.