Structural and magnetic properties of zinc ferrite incorporated in amorphous matrix

Glass ceramics in the (Fe₂O₃)_x·(B₂O₃)_(60−x)·(ZnO)₄₀ (x = 17.5 and 20 mol%) system were prepared by the melt-quench method and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and magnetization measurements. The samples contain a unique magnetic crystalline phase, the zinc ferrite (ZnFe₂O₄), embedded in an amorphous matrix. The ZnFe₂O₄ crystals precipitate during cooling from melting temperature. From the XRD data, the average unit-cell parameter, crystallite size and the quantitative ratio of the crystallographic phases in the samples were evaluated. FTIR data revealed that the BO₃ and BO₄ are the main structural units of these glass ceramics network. FTIR spectra of these samples show features at characteristic vibration frequencies of ZnFe₂O₄. From the magnetization curves it was found that the nanoparticles exhibit ferromagnetic interactions combined with superparamagnetism with a blocking temperature, T_B, which is composition dependent. In all samples hysteresis is present below T_B. The coercive field is dependent on composition and magnetic field being around 0.05μ_B/f.u. for measurements performed in maximum 0.4 T. Finally, the magnetic behavior of iron in this system is discussed.