Félix Sánchez De Jesús

Magnetic Properties of Nanostructured Spinel Ferrites

Spinel ferrite nanoparticles (NPs) have raised interest due to their potential technological applications in fields as varied as high frequency electronic device components, soil remediation, and medical diagnosis and treatments. In this paper, we present a brief review of the magnetic properties of spinel ferrite NPs (Ni-Zn, Co, and magnetite) synthesized by the polyol method, in different degrees of aggregation, from monodisperse NPs, to clusters formed by tens to hundreds of NPs. We show that the approach to saturation can be modeled with a relationship derived from the Stoner-Wohlfarth model, both for ferrimagnetic and superparamagnetic NPs. We also present a review on the magnetic properties of spinel ferrites NPs consolidated using spark plasma sintering (SPS). This technique allows the sintering of NPs to densities 90% of the theoretical value at significantly lower temperatures and shorter times than the typical sintering processes, preserving the grain size within the nanometric range. The typical sintering temperatures are in the range 350°C-750°C, for times as short as 5 min. An interesting example is magnetite, which can be obtained as NPs by polyol, followed by SPS at 750°C, temperature that usually leads to the transformation to hematite. The Verwey transition is clearly observed as a large drop in the coercive field at ~120 K.

Mechanosynthesis, Crystal Structure and Magnetic Characterization of Neodymium Orthoferrite

Neodymium orthoferrite NdFeO3 was obtained at room temperature by mechanosynthesis with a stoichiometric ratio of Nd2O3 and Fe2O3 powders, whereas the traditional synthesis requires a temperature of approximately 1000 °C. The crystal structure was analyzed by X-ray diffraction analysis using Cu radiation and a LynxEye XE detector, whose strong fluorescence filtering enabled a high signal intensity. The analysis indicated that the obtained crystallites were nano-sized. The particle morphology was observed by scanning electron microscopy, and the magnetic saturation was tested by vibrating sample magnetometry. The synthesis of NdFeO3 was detected after a few hours of milling, indicating that the milling imparted mechanical energy to the system.

Enhancement in Curie Temperature of Yttrium Iron Garnet by Doping with Neodymium

The effect of the substitution of Y3+ by Nd3+ on the structural and magnetic properties of neodymium-doped yttrium iron garnet, NdxY3−xFe5O12 with x in the range of 0–2.5, is presented. Oxide powders of Fe2O3, Nd2O3, and Y2O3 were mixed in a stoichiometric ratio and milled for 5 h using high-energy ball milling, before being uniaxially pressed at 900 MPa and annealed at 1373 K for 2 h to obtain NdxY3−xFe5O12 (0 ≤ x ≤ 2.5). It was found that the mechanical milling of oxides followed by annealing promotes the complete structural formation of the garnet structure. Additionally, the X-ray diffraction patterns confirm the complete introduction of Nd3+ into the garnet structure with a neodymium doping concentration (x) of 0–2.0, which causes a consistent increment in the lattice parameters with the Nd3+ content. When x is higher than 2.0, the yttrium orthoferrite is the predominant phase. Besides, the magnetic results reveal an increase in the Curie temperature (583 K) as the amount of Nd3+ increases, while there was enhanced saturation magnetization as well as modified remanence and coercivity with respect to non-doped YIG.

Characterization of Ceramic Materials synthesized by Mechanosynthesis for Energy Applications

The close relationship between processing, structure and properties of materials is well known. Some of the most useful tools to elucidate the best choice in processing for a given application are scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), selected area electron diffraction (SAED) and x-ray diffraction (XRD). In this chapter we will focus on the application of these techniques to the characterization of ceramic materials processed by mechanosynthesis, evaluating the effect of the milling process on their physical properties.