| Ferrite materials are widely used in electronics, information, machinery and other industrial areas. Ferrite is a magnetic material has a unique high resistivity and good high frequency characteristics. Those properties have attracted considerable interest in recent years since they might offer the potential to enhance the performance or shrink the dimensional sizes of the microelectronic devices. At present, the ferrite materials are becoming an important research field of the magnetic materials. In the present work, NiFe2O4 (NFO) is one of the most versatile and technologically important ferrite materials. BaTiO3 (BTO) material is a typical ferroelectric material, so it has great application prospect in the electric tuning microwave components.The standard double sintering ceramic method was used to prepare the 0.45NFO-0.55BTO composite ceramic. Complex impedance spectroscopy of 0.45NFO-0.55BTO composite ceramic on the electrical characteristics were studied. The grain resistance, grain boundary resistance and relaxation time constant were calculated from the Cole-Cole plot. Impedance spectroscopy measurements were conducted in a frequency range from 20 Hz to 2 MHz and in a temperature range from 348 to 473 K. The impedance measurements have also shown the evidence of grain boundary conduction and lowering of barrier to the motion of charge carriers with rise in temperature. Using the Arrhenius plot of dc conductivity, the corresponding activation energy for both grain and grain boundary were 0.32 eV and 0.38 eV, respectively. The values revealed that the composite ceramic was attributed to the motion of oxygen vacancies within the bulk. We also found that the relaxation frequency shift to high side with increase in temperature. In addition, the sample exhibits hysteresis loop typical of magnetic behavior. The saturation magnetization increases from 2.38 to 3.13 emu/g and the coercivity increases from 0.2 to 0.7 Oe with increasing temperature.Nickel ferrite NiFe2O4 (NFO) thin films have been prepared on Si substrate (NFO/Si) and on La0.7Sr0.3MnO3 (LSMO)-coated Si (100) substrate (NFO/LSMO/Si) by RF magnetron sputtering. The microstructures and magnetic properties of the two films were systematically investigated. X-ray diffraction (XRD) and scanning electron microscope (SEM) revealed that the high (331)-oriented NFO films were grown on LSMO/Si substrate with smooth surface and cross-section morphologies. The samples show a clear hysteresis loop with in-plane H the magnetization. However, both samples do not show any hysteresis with the magnetic field applied perpendicular to the films plane, which indicates the presence of an anisotropy favoring the orientation of the magnetization in the direction parallel to the films plane. Study of magnetization hysteresis loop measurements reflects that LSMO buffer layer may improve the magnetic properties of NFO thin films, and the saturation magnetization increases from 41.5 to 350 emu/cm3.We also explored the influence of different growth atmosphere to the structure and properties of NFO films. NFO thin films on Si (100) substrate have been prepared by RF magnetron sputtering. The growth atmosphere consisted either of pure Ar or of a Ar/O2 mixture. The results show that both of the films deposited by two kinds of atmospheres exhibit spinel structure, and the preferential orientation changes when adding some oxygen. In addition, it is found that the magnetic properties of the deposited NFO films with oxygen are significantly improved(MS=41.5 emu/cm3). |
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