Electrical and Magnetic Properties of Yttrium Ferrites

Abstract

The development of new materials with a high dielectric constant and low losses is one of the main targets in scientific research for applications. These properties permit to reduce the size and weight of electronic devices. A potential candidate for this goal is yttrium ferrite. Powder precursors of yttrium ferrites, Y₃Fe₅O₁₂ (YIG) and YFeO₃, were prepared by the sol-gel method through the Pechini route. The powders were heat-treated at 1000, 1300 and 1400 °C. The sample structure was characterized by X-ray diffraction (XRD), the morphology by scanning electron microscopy (SEM). For all temperatures of the heat-treatment, the YIG crystalline phase was the predominant and YFeO₃ the secondary phase. The highest percentage of YIG (≈90%) was obtained in the samples heat-treated at 1400 °C. By means of impedance spectroscopy measurements, the dielectric properties were studied between 100 Hz and 1 MHz, and between 200 and 400 K. The dielectric constant improves with the growth of the YIG phase, increasing grain size and decreasing porosity . The highest value of dielectric constant at 1 kHz was obtained for the sample heat-treated at 1400 °C (ε′ = 1750; tan δ = 0.18). The values of dielectric losses are sufficiently low to use this material in electronic applications. For all samples, one non-Debye relaxation process was identified; the relaxation time versus temperature shows an Arrhenius behaviour. Magnetic measurements (M vs. T and M vs. B) were performed using a vibrating sample magnetometer (VSM). The dc magnetic susceptibility was recorded under zero field cooled (ZFC) and field cooled (FC) sequences, with a field of 0.1 T between 7 and 300 K. The results of the magnetic investigations show the presence of a blocking temperature, T_B ≈ 50 K for the sample treated at 1000 °C and T_B ≈ 250 K for samples treated at 1300 and 1400 °C, respectively. The saturation magnetization slightly decreases with the temperature of measurement being of ≈35 Am²kg⁻¹ at 7 K and ≈25 Am²kg⁻¹ at 300 K.