Dependence of pH Variation on the Structural, Morphological, and Magnetic Properties of Sol-Gel Synthesized Strontium Ferrite Nanoparticles

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

Spin-Coating Technique for Fabricating Nickel Zinc Nanoferrite (Ni0.3Zn0.7Fe2O4) Thin Films

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

Sintering Temperature Effect on Microstructure and Magnetic Evolution Properties with Nano- and Micrometer Grain Size in Ferrite Polycrystals

The morphology and evolution of magnetic properties in multisample sintering (MSS) of yttrium iron garnet (Y3Fe5O12, YIG) and single-sample sintering (SSS) of nickel zinc ferrite (Ni0.6Zn0.4Fe2O4, NZF) were studied in detail, focusing on the parallel evolving relationship with their dependences on sintering temperature. Sintering is an important process in ferrite fabrication which involved the process of transforming a noncrystalline powder into a polycrystalline solid by heating process. Under the influence of heat, the surface area is reduced through the formation and growth of bond between the particles associated with reduction in surface energy. This makes the particles move closer, grains to form by the movement of grain boundaries to grow over pores, and results in decreasing the porosity and increasing the density of the sample. Technological applications, especially in electronics applications, require high-density nanostructured ferrites, integrated by sintering from nanoparticles. The evolution from low to high sintering temperature will result in the transition from disordered to ordered ferromagnetism behavior. Multisample sintering (MSS) of yttrium iron garnet (Y3Fe5O12, YIG) and single-sample sintering (SSS) of nickel zinc ferrite (Ni0.6Zn0.4Fe2O4, NZF) have been used as a studied material in this research work

Enhancing absorption properties of Mg–Ti substituted barium hexaferrite nanocomposite through the addition of MWCNT

M-type barium ferrite with Mg–Ti substitution and MWCNT addition was synthesized using high-energy ball milling. The prepared sample was further analyzed using X-ray diffraction, field emission scanning electron microscope (FESEM), vibrating sample magnetometer and vector network analyzer. The results showed that the particle size had a wide range of distribution, and a hexagonal structure was formed in the sample. The sample was observed to have lower saturation magnetization and coercivity after Mg–Ti was substituted with MWCNT and added into the barium hexaferrite. Reflection loss was studied as a function of frequency and thickness of the sample. For Mg–Ti substituted barium hexaferrite composite with a thickness of 2.0 mm, the reflection loss peaked at −28.83 dB at a frequency of 15.57 GHz with a bandwidth of 6.43 GHz at a loss of less than −10 dB. The microwave absorption primarily resulted from magnetic losses caused by magnetization relaxation, domain wall resonance, and natural resonance. FESEM micrograph demonstrated that carbon nanotubes were attached to the external surface of the ferrite nanoparticles. The investigation of the microwave absorption indicated that with an addition of carbon nanotubes, the real and imaginary parts of permittivity and reflection loss had enhanced to −34.16 dB at a frequency of 14.19 GHz with a bandwidth of 5.72 GHz

Evolution of Nanometer-to-Micrometer Grain Size in Multiferroic Properties of Polycrystalline Holmium and Yttrium Manganite

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

Magnetic phase-transition dependence on nano-to-micron grain-size microstructural changes of mechanically alloyed and sintered Ni0.6Zn0.4Fe2O4

The microstructure evolution in several polycrystalline Ni0.6Zn0.4Fe2O4 samples as a result of a sintering scheme was studied in detail, in parallel with the changes in their magnetic properties. The Ni0.6Zn0.4Fe2O4 toroidal sample was prepared via mechanical alloying and subsequent molding; the sample with nanometer-sized compacted powder was repeatedly sintered from 600 to 1200 °C with an increment of 25 °C. An integrated analysis of phase, microstructural and hysteresis data pointed to existence of three distinct shape-differentiated groups of B–H hysteresis loops which belong to samples with weak, moderate and strong magnetism (Idza in Mater. Res. Bull. 47:1345–1352, 2012), respectively. The real permeability, μ′, and loss factor, μ″, increased with grain size which increased due to increase in sintering temperature and these two magnetic properties also seem to belong to three value-differentiated groups corresponding to the same temperature ranges found for the B–H groupings. These groupings are tentatively explained using Snoek’s Law

Sol-gel auto-combustion synthesis of cobalt ferrite and it's cytotoxicity properties

Cobalt ferrite (CoFe2O4) nanoparticles were successfully synthesized by a sol-gel combustion technique. The particle size as determined by a transmission electron microscope was about 25 nm. A maximum saturation magnetization of 22.31 emu/g and a coercivity of 118 Oe were achieved for the samples. The effect of CoFe2O4 nanoparticles on 4T1 murine breast cancer cells was explored by cytotoxicity assay and flow cytometer analysis. The lower concentrations of CoFe2O4 nanoparticles did not induce any toxicity in cells, when exposed for 24 h. Concentrations exceeding 400 μg/ml produced significant morphological changes and induced cell death by apoptosis and necrosis

Co–Ti- and Mn–Ti-substituted barium ferrite for electromagnetic property tuning and enhanced microwave absorption synthesized via mechanical alloying

Substituted barium hexaferrite nanoparticles with nominal composition of BaCo1.0Ti1.0Fe10O19 and BaMn0.8Ti0.8Fe10.4O19 were synthesized by high energy ball milling (HEBM). The effects of Co–Ti and Mn–Ti substitution on their microstructure, electromagnetic properties, and microwave absorptive behavior were analyzed. The samples were structurally characterized by X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray analysis (EDX). The M-H loops of the composites were determined with a vibrating sample magnetometer (VSM), and the interaction with the microwave radiation in the range of 8–18 GHz of the nanocomposites dispersed in epoxy resin was measured with a vector network analyzer (VNA). This study suggests that by controlling the grain size and different elements of substitution would give a decrease in coercivity and enhanced values of complex permittivity in order to improve microwave absorption. The dielectric constant and loss were enhanced in comparison to the permeability constant and loss over the entire frequency range. Finally, microwave measurement showed that the substituted barium hexaferrite sample with Co–Ti and Mn–Ti could be used as an efficient microwave absorption material with an appropriate absorption at −31.27 and −26.73 dB, respectively. The predicted absorption and reflection loss demonstrates that Co–Ti and Mn–Ti substitution gives low reflectivity at microwave frequency and is a good candidate for electromagnetic materials for radar wave applications

Trends of parallel microstructure and magnetic properties evolution in Co0.5Zn0.5Fe2O4

The present paper reports on an effort to expose and scientifically explain the microstructure–magnetic properties relationship as they evolve with increasing sintering temperature. Mechanical alloying was used to prepare cobalt–zinc ferrite nanoparticles with sintering temperature from 800 to 1,350 °C with 50 °C increment. The microstructure of the samples was observed using a field emission scanning electron microscope, and the magnetic parameters, such as the real permeability and loss factor, were measured at room temperature in the frequency range from 10 MHz to 1.0 GHz using an Agilent 4291B impedance/material analyzer. The B–H hysteresis of the samples was investigated using a MATS-2010SD Static Hysteresisgraph. From the results, the real permeability and loss factor were observed to increase up to 1,250 °C. These increases corresponded to increases in grain size and are mainly due to easier domain wall movement. However, due to zinc loss, μ′ and μ′′ as well as the saturation induction decreased from 1,300 to 1,350 °C. The coercivity increased up to 850 °C and decreased with increasing temperature. This increasing-to-decreasing coercivity trend corresponded well with the single- to multi-domain grain size transition marked by critical grain size at about 0.13 μm

Effect of temperature towards rice husk silica characterization with different preparation methods

Rice Husk Ash (RHA) ceramic presented in this paper undergoes different preparation methods. This study reported a comparison in terms of product quality, yield, structure and processing time between acid leaching techniques (HCl) to the other non-treated acid leaching. In this research, the White Rice Husk Ash (WRHA) pellets were prepared by cleaning the Rice Husk (RH) with distilled water and HCl acid respectively. The raw material, RH was going through thermal treatment in order to produce white ash powder then milled into nano-sized powder via high-energy ball milling (HEBM). To subject the samples to a series of temperatures, the pressed pellets went through multi-sample sintering, where the samples were sintered at 800ºC, 1000ºC, 1100ºC and 1200ºC for each batch. The percentage of density and porosity respectively increases and decreases with the increasing of sintering temperature. During the sintering process, the grain size increased, which caused less porosity and giving higher density in the sample. The comparative XRD plot of the sintered samples at various temperatures prepared by different cleaning route showed the difference between the amorphous and crystalline silica. The XRD spectra reveal that the main phase for crystallization was cristobalite and tridynamite. The FESEM images displayed the comparative morphological features of the samples. The grain sizes were observed to be smaller by acid leach treatment. Acid leaching of rice husks prior to combustion resulted in smaller particle size, larger surface area in comparison with ash from non-acid treated husks (NTR)