Magnetic characteristics adjustment through rare-earth lanthanum substitution in mechanically alloyed yttrium iron garnet nanoparticles

Yttrium iron garnet (YIG) is a very important ferrimagnetic ceramic and widely used in high frequency magneto-optical applications due to its high saturation magnetisation and low magnetic loss up to several GHz. Magnetic properties of YIG are strongly dependent on the processing technique, in which small amount of dopants can largely affect its properties. In this study, the effect of various lanthanum (La) content on structural, microstructural and magnetic characteristics of YIG was reported. The nanosized powders of La-subtituted YIG with La content of 0.0 to 0.5 were synthesised using mechanical alloying technique for 6 h followed by sintering at 1400°C. The physical characteristics of the samples were analysed using XRD, FTIR, TEM and SEM, meanwhile the magnetic and thermomagnetic characteristics of the samples were measured using VSM and LCR-meter respectively. The particle size of as-milled samples showed an increment from 38 to 53 nm with increasing La content and the XRD patterns of the samples showed evidently a highly crystalline and full phase YIG ferrite, regardless of its La content. While the microstructure of the samples barely remains consistent for all La content, the saturation magnetisation of the samples showed reduction with increasing La content. This is due to the magnetic dilution caused by La in overall superexchange interaction in magnetic moments of YIG, which is attributed to the paramagnetic nature of La rare earth ions at room temperature

Evolution of Magnetic Properties in Ferrites: Trends of Single- Sample and Multi-Sample Sintering

Microstructure of magnetic materials greatly influences the performance of magnetic properties, and sintering has been used as an agent to tailor the microstructure of these magnetic materials especially ferrites. Nanostructured ferrites prepared by high-energy milling method are often inherently unstable owing to their small constituent sizes, non-equilibrium cation distribution, disordered spin configuration, and high chemical activity. Therefore, sintering of the milled ferrites recrystallizes the nanostructure and causes its transition from an excited metastable (activated) state into the low-energy crystalline state. A better understanding of the response of nanoscale ferrites with changes in temperature is crucial not only for basic science (the development of an atomistic and microscopic theory of the mechanochemical processes) but also because of the technological high-temperature applications in catalysis, ferrofluids and information storage. This chapter discusses on two different sintering schemes, which are a commonly applied multi-sample sintering and a rarely adopted single-sample sintering. Experimental results of single-sample and multi-sample sintering of NiZn ferrites and yttrium iron garnet (YIG) were highlighted, and their microstructural consequences on the magnetic properties were also discussed

Microwave sintering of Ni-Cr doped strontium hexaferrite synthesized via sol-gel method

The magnetic behavior of Strontium hexaferrite ceramics with nominal composition SrFe12-2xNixCrxO19 (where x = 0.2, 0.4, 0.6, 0.8) samples are reported in this paper. Four samples were synthesized by the sol-gel method. The XRD analysis confirms the single phase and various parameters such as lattice constants (a and c), are calculated from the XRD data. Magnetic properties, such as specific saturation magnetization (Ms) and coercivity (Hc) are calculated from the hysteresis loops. Values of coercivity are found to increase up to the substitution level of x = 0.0-0.2 and then decreases continuously while that of saturation magnetization decrease continuously with increase in Ni-Cr concentration. The results show that microwave sintering requires about 75% less processing time than required by conventional method and still provides better magnetic properties

Tailoring the Structural and Optical Properties of Oxychloride Magnesium Tellurite Glass with the Addition of Samarium Ions

In this study, samarium-doped oxychloride magnesium tellurite glass with composition (79−x)TeO2−xMgO−20Li2O−1Sm2O3 (Series 1) and (79−x)TeO2xMgCl2−20Li2O−1Sm2O3 (Series 2) with 0 ≤ x ≤ 15 mol% was prepared by the melt-quenching technique. The structural and optical properties of synthesized samples were investigated, and the XRD results dictated an amorphous nature for both samples. The glass density of both Series 1 and 2 decreased with increasing MgO and MgCl2 content. However, the molar volume behaves in a completely opposite manner to an increase in MgO or MgCl2 content. FTIR spectra revealed from the vibrational wavenumber shift of TeO4 and TeO3 structural units showed a significant rise in HOH vibration mode, which implies its usefulness in boosting water and light absorption. Four absorbance bands were observed via UV-Vis NIR, while the indirect optical band gap around (3.42–3.36) eV and (3.42−3.30) eV for Series 1 and Series 2 were observed from UV-Vis spectroscopy. The emission spectra from the photoluminescence study revealed four distinct bands centered at 562.54, 599.14, 645.63 and 708.40 nm which are attributed to the transition from 4G5/2 – 6HJ/2 (J = 5,7,9,11) of states of Sm3+. The optimum glass with a composition of TeO-MgO 15% demonstrates a high potential for optical device development

Structural and Magnetic Characteristics Evaluation of Iron Oxide Extracted from Printer Toner Wastes

The need to recycle and develop valuable materials from wastes, and use them in various applications have become increasingly important in recent decades. Printer toner waste is one of the most polluting electronic wastes due to the toxic nature of the material content inside it. Despite the toxicity of the material in the toner powder, it contains iron oxide that can be extracted and recycled to make a beneficial material. Therefore, this study aims to investigate a facile and effective method to extract iron oxide from printer toner waste powder. Magnetic separation and oxidation processes were used as a method for extraction and phase conversion. The structural transformation was investigated using X-ray diffraction (XRD), microstructural observation using scanning electron microscope whereas static magnetic characteristics were investigated using vibrating sample magnetometer. The results from XRD spectra showed that printer toner wastes that have been subjected to magnetic separation process and chemical treatment, even without any heat treatment process, have produced a single-phase magnetite. Through the process of heat treatment on the sample, phase transformation from magnetite to hematite occurred, in which a single phase of hematite is obtained at a temperature of 1400 °C. The saturation magnetization of the sample also showed a reduction where the sample before undergoing the heat treatment process had a saturation magnetization value of 18.81 emu/g but after the heat treatment, the saturation magnetization value decreased to 0.42 emu/g. These results are in line with the phase transformation shown where magnetite has high ferrimagnetic characteristics, whereas hematite is basically antiferromagnetic at room temperature. However, the saturation magnetization that has been obtained in hematite shows a little difference to that of commercially sold hematite. This proves that iron oxide extracted from the printer toner waste has high potential as an alternative to commercial iron oxide available in producing high-performance magnetic materials

Waste-to-wealth : From printer toner waste into valuable magnetic materials

To recover magnetite (Fe2O3) by magnetic separation technique and convert into Fe2O3 using reduction technique. To synthesize Nickel Zinc Ferrite (NZF) using extracted iron oxide from waste toner powder. To study the structural, microstructural and magnetic properties of Nickel Zinc Ferrite (NZF) prepared using extracted Fe2O3 as main component

Dependence of developing magnetic hysteresis characteristics on stages of evolving microstructure in polycrystalline yttrium iron garnet

The microstructure evolution in several polycrystalline yttrium iron garnet samples as a result of a sintering scheme was studied in detail, in parallel with the changes in their magnetic properties. Samples with nanometer sized starting powder were synthesized by employing the High-Energy Ball Milling technique and then sintering toroidal compacts of the milled powder. Nine sintered samples were obtained, each corresponding to a particular sintering from 600 °C to 1400 °C. The samples were characterized for their evolution in crystalline phases, microstructure and magnetic hysteresis-loops parameters. The results showed an increasing tendency of the saturation magnetization and saturation induction with grain size, which is attributed to crystallinity increase and to reduction of demagnetizing fields in the grains. The variation in coercivity could be related to anisotropy field changes within the samples due to grain size changes. In particular, the starting appearance of room temperature ferromagnetic order suggested by the sigmoid-shaped B–H loops seems to be dependent on a sufficient number of large enough magnetic domain-containing grains having been formed in the microstructure. Viewed simultaneously, the hysteresis loops appear to belong to three groups with different magnetism-type dominance, respectively dependent on phase purity and three different groups of grain size distributions

Recent developments of smart electromagnetic absorbers based polymer-composites at gigahertz frequencies

The rapid increase in electromagnetic interference has received a serious attention from researchers who responded by producing a variety of radar absorbing materials especially at high gigahertz frequencies. Ongoing investigation is being carried out in order to find the best absorbing materials which can fulfill the requirements for smart absorbing materials which are lightweight, broad bandwidth absorption, stronger absorption etc. Thus, to improve the absorbing capability, several important parameters need to be taken into consideration such as filler type, loading level, type of polymer matrix, physical thickness, grain sizes, layers and bandwidth. Therefore, this article introduces the electromagnetic wave absorption mechanisms and then reveals and reviews those parameters that enhance the absorption performance

Sintering temperature dependence of optimized microstructure formation of BaFe12O19 using sol–gel method

In an attempt to obtain the best possible properties of barium hexaferrite (BaFe12O19), the sol–gel synthesis method was chosen and, the optimum sintering conditions were established. The effects of the sintering temperature on the structural, morphological and magnetic properties of hexaferrite were studied. X-ray analysis indicates that the sintered samples (1,000–1,150 °C) remained in the hexagonal structure. From this analysis, no secondary phases are identified. The effect of sintering temperature on the grain growth of BaFeBaFe12O19 is confirmed by the microstructure using HR-SEM and is in good agreement with the XRD analysis based on the peak intensity of the (107) plane. The samples sintered at 1,150 °C showed the densities as ~93 % of theoretical density. Sintering temperature affected the grains in compact samples. The results show that homogeneous and dense BaFeBaFe12O19 ceramics obtained at a lower sintering temperature of 1,150 °C which is lower than the normally reported sintering temperature of ≥1,200 °C. The thermal treatment can markedly affect the grains in compact samples

Magnetic and microwave properties of polycrystalline gadolinium iron garnet

The microwave loss in nanosized GdIG particles synthesized using mechanical alloying technique was investigated. There were very few of research on the microwave properties of nanosized particle GdIG and there is no attempt investigating on the material at C-band frequency range and its correlation with the microstructure. Gadolinium (III) iron oxide and iron (III) oxide, α-Fe2O3 were used as the starting materials. The mixed powder was then milled in a high-energy ball mixer/mill SPEX8000D for 3 hours. The samples were sintered at temperature 1200°C for 10 hours in an ambient air environment. The phase formation of the sintered samples was analyzed using a Philips X’Pert Diffractometer with Cu-Kα radiation. Complex permeability constitutes of real permeability and magnetic loss factor were measured using an Agilent HP4291A Impedance Material Analyzer in the frequency range from 10 MHz to 1 GHz. A PNA-N5227 Vector Network Analyzer (VNA) was used to obtain the information on ferromagnetic linewidth broadening, ΔH that represents the microwave loss in the samples in in frequency range of 4 to 8 GHz (C-band). The ΔH value was calculated from the transmission (S21) data acquired from VNA. The single phase GdIG showed low initial permeability and low magnetic loss when applied with low-frequency range energy. From these data, it is validated that GdIG is a suitable material for microwave devices for the high-frequency range