In this research work, an attempt of regulating the pH as a sol-gel modification parameter during preparation of SrFe12O19 nanoparticles sintered at a low sintering temperature of 900°C has been presented. The relationship of varying pH (pH 1–14) on structural microstructures and magnetic behaviors of SrFe12O19 nanoparticles was characterized by X-ray diffraction (XRD), field emission scanning microscope (FESEM), thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR), and vibrating-sample magnetometer (VSM). The single-phase SrFe2O19 with optimum magnetic properties can be obtained at pH 1 with a sintering temperature of 900°C. As pH values increase, the presence of impurity Fe2O3 was observed. TGA data-varying pH shows that the total weight loss of most samples was at 30.44% which corresponds to the decomposition process. The IR spectra showed three main absorption bands in the range of 400–600 cm−1 corresponding to strontium hexaferrite. SEM micrographs exhibit a circular crystal type of strontium ferrite with an average crystal size in the range of 53–133 nm. A higher saturation magnetization Ms, remanent magnetization Mr, and hysteresis Hc were recorded to have a large loop of 55.094 emu/g, 33.995 emu/g, and 5357.6 Oe, respectively, at pH 11, which make the synthesized materials useful for high-density recording media and permanent magnets.
Part of the book: Sol-Gel Method
Functional nanoferrite thin films are used in various fields of our life. There are many different methods used to fabricate thin films including sputter deposition, flash laser evaporation pulsed laser deposition (PLD), chemical vapor deposition (PVD) and spin-coating process. In each of these methods, it produces an amorphous phase of the deposited film. To produce a crystalline film, an additional high-temperature processing is required. The high-temperature process can lead to considerable constraints in combining the desirable characteristics of a crystalline nanoferrite thin film with those of thermally unstable substrates and other device components. High-temperature thin-film processing is also a considerable cost to manufacturing. This chapter will report a simple procedure of the sol-gel precursor method for fabrication of NiZn nanoferrite (Ni0.3Zn0.7Fe2O4) thin films and spin-coating method in coating a chemical solution. This method generally provides for both low-temperature deposition and crystallization of NiZn nanoferrite thin films.
Part of the book: Coatings and Thin-Film Technologies
The parallel evolution of microstructure development via grain size changes from a nano-to-micron size regime toward multiferroic property development has been established in this research work. This kind of observation is not present in the literature in this research area, and studies of the link between morphological properties and ferroelectric properties of multiferroic materials have been focusing solely on the product of the ultimate sintering temperature, mostly neglecting the parallel evolutions of morphological properties and their relationship at varied chosen sintering temperatures. Holmium manganese oxide and yttrium manganese oxide were both prepared via high-energy ball milling (HEBM) in a hardened steel vial for 12 h. The pressed pellet went through multi-sample sintering, whereas the samples were sintered starting from 600 to 1250°C with 50°C increments for any one sample being subjected to only one sintering temperature. Orthorhombic HoMn2O5 and YMn2O5 phases were observed to exist in both as milled powder. The degree of crystallinity increased with increasing sintering temperature. Hexagonal HoMnO3 peaks were observed for sintering temperature ≥1050°C. As for YMnO3 series, the single phase of hexagonal YMnO3 started to appear at sintering temperature ≥1000°C. FESEM micrographs revealed that as the sintering temperature increased, the grain size increased, consequently increasing the geometric ferroelectric behavior. The polarization-electric field (P-E) plot reveals that HoMnO3 and YMnO3 are highly leaky ferroelectrics with a P-E curve shape different from the normal shape of highly insulating ferroelectrics. It shows that the remanent polarization and electric field increased generally with increasing grain size. For both series, there existed a difference based on their difference of crystallinity, microstructure data, and phase purity changes. Larger grain size is known to give ease for polarization to take place.
Part of the book: Functional Materials