A.M. Bolarín-Miró

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.

Structural Analysis and Magnetic Properties of FeCo Alloys Obtained by Mechanical Alloying

A systematic study on the structural and magnetic properties of alloys (, in wt. percent) obtained by mechanical alloying is presented. Elemental powders of Fe and Co mixed in an adequate weight ratio were milled at room temperature in a shaker mixer mill using vials and balls of hardened steel as milling media with a ball : powder weight ratio of 12 : 1. The mixtures were milled for 3 h. The results show that, after milling, for almost all the composition (up to ), solid solutions based on bcc structures were obtained. For Co-rich alloys (), different phases were found, revealing the formation of a metastable intermetallic phase (FeCo, wairauite) together with fcc-Co and hcp-Co phases. The specific saturation magnetization increases by increasing Co content, reaching a maximum value of 225 emu/g for hcp-Fe70Co30, and then it shows a diminution up to 154 emu/g for bcc-Fe30Co70. All studied alloys () present low coercivity, in the range from 0 to 65 Oe, which is lower than reported. The coercivity increases with the increment in Co, reaching a maximum of 64.1 Oe for Fe40Co60. After that, the coercivity falls up to 24.5 Oe for Co-rich alloys, which make them a very low coercive material.

Synthesis of PZT Ceramics by Sol-Gel Method and Mixed Oxides with Mechanical Activation Using Different Oxides as a Source of Pb

J. M. Yanez-Limon1, G. Rivera-Ruedas1, F. Sanchez De: Jesus2, A. M. Bolarin-Miro2, R. Jimenez Rioboo3 and J. Munoz-Saldana1 1Centro de Investigacion y Estudios Avanzados del IPN. Unidad Queretaro. Libramiento Norponiente No. 2000 Fracc. Real de Juriquilla, Queretaro, Qro 2Area Academica de Ciencias de la Tierra y Materiales, Universidad Autonoma del Estado de Hidalgo, CU, Carr. Pachuca-Tulancingo, Pachuca, Hgo, 3Instituto de Ciencia de Materiales de Madrid Consejo Superior de Investigaciones de Cientificas Cantoblanco, Madrid, 1,2Mexico 3Spain

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.

Development of process technologies for improvement of electroless nickel coatings properties

This paper describes research and technology developments that enable to improve nickel electroless coating properties. This work deals with: (a) different methods in order to achieve Ni-P-Mo coatings. (b) Other development is related with coatings with addition of hard particles such as SiC, WC or Al2O3,(c) Electroless nickel deposits on PBT and austempered ductile iron (ADI). (d) In addition, nickel coatings were deposited on powder metallic pieces and finally, electroless nickel coatings, in conjunction with layers from thermal spray process were formed. Characterization of all coatings by means of optical microscopy, scanning electron microscopy, micro-hardness, wear and corrosion tests were carried out. Results indicate positive increment in both mechanical and electrochemical properties which enhance field applications in Mexican industry.

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.