Effect of milling process on particle size, morphology and magnetization in non-stoichiometric Fe2O3-MnO2.

High-energy milling process on ceramic material was analyzed, it process generate modifications on morphology and particle size, the process showed the last one relation with the crystallite size, about of structural analysis Rietveld refinement let identify anisotropy with the variations on crystalline planes and deformations occasioned by milling process, the particle size decrease with the process, similar tendency was observed on the images obtained by Scanning Electronic Microscopy, an result in this study was the variation on magnetization without chemical reaction under non-stoichiometric conditions and the agglomerates sizes observed on samples it is by process

Estudio cinético y mecanismos de reacciones en el proceso de depósito de aleaciones ternarias de Ni-P-Mo

Un depósito de Ni-P-Mo vía química genera un recubrimiento ingenieril empleado por su buena resistencia al desgaste y a la corrosión Los recubrimientos químicos Ni-P-Mo se obtienen por depósito auto catalítica empleando una solución de composición específica, en la que el sustrato cataliza la reacción. El objetivo de este trabajo es determinar la cinética de la reacción de depósito de recubrimientos autocatalíticos Ni-P-Mo de un baño de composición específica, a través de la determinación del consumo en reactivos, el incremento en peso del sustrato recubierto, el espesor y la microdureza del recubrimiento. Se encontró una velocidad media para el depósito de 1.61 mg.min-1cm-2, pero ésta es diferente para cada elemento. Durante la depósito, el factor determinante en la velocidad de depositación es el Mo debido a que (1) su depósito se inhibe por la presencia de fósforo en la solución que se codeposita con el níquel y (2) incrementos en la concentración de molibdato en la solución la hacen inestable. Los resultados obtenidos permiten proponer el mecanismo de codepósito Ni-P-Mo, a través del planteamiento de las reacciones que tienen lugar durante el proceso de depositación

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

Effect of Sonication Output Power on the Crystal Structure and Magnetism of SrFe12O19 Nanoparticles

We reported the effect of the sonication output power (SOP), from 120, 180, to 240 W, on the crystal structure, morphology, and magnetic properties of SrFe12O19 nanoparticles synthesized by sonochemical process assisted with heat treatment. X-ray Diffraction analysis of the obtained powder showed the formation of Fe3O4 with low crystallinity degree, which increased with the increase in SOP, together in a crystalline phase identified as SrCO3. The formation of SrFe12O19 started at 1073 K, and was completed at 1173 K. However, hexaferrite was obtained with the secondary phases α-Fe2O3 and SrFeO2.5. At 1323 K, the secondary phases vanished, and a single phase SrFe12O19 was detected. Vibrating Sample Magnetometry analysis showed that the SrFeO2.5 phase caused the formation of a hysteresis loop known as the Perminvar magnetic hysteresis loop. At 1323 K, the powder synthesized at 120 W showed a specific magnetization of 67.15 Am2/kg at 1.43 × 106 A/m, and coercivity of 4.69 × 104 A/m, with a spherical-like morphology and average particle size of 56.81 nm obtained by Scanning Electron Microscopy analysis. The increment of SOP promoted a high degree of crystallinity and decrease in crystal size. Additionally, it promoted the formation of secondary phases, induced agglomeration, and modified the morphology of the particles

Enhanced Multiferroic Properties of YFeO3 by Doping with Bi3+

Tthe present work studied the cationic substitution of Y3+ by Bi3+ on the crystal structure of orthorhombic YFeO3 and its effect over magnetic, dielectric and electric properties of multiferroic yttrium orthoferrite. Stoichiometric mixtures of Y2O3, Fe2O3 and Bi2O3 were mixed and milled for 5 h using a ball to powder weight ratio of 10:1 by high-energy ball milling. The obtained powders were pressed at 1500 MPa and sintered at 700 °C for 2 h. The test samples were characterized at room temperature by X-ray diffraction (XRD), vibrating sample magnetometer (VSM), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and impedance spectroscopy (IS). The X-ray diffraction patterns disclosed a maximum solubility of 30 % mol. of Bi3+ into the orthorhombic YFeO3. For higher concentrations, a transformation from orthorhombic to garnet structure was produced, obtaining partially Y3Fe5O12 phase. The substitution of Bi3+ in Y3+ sites promoted a distortion into the orthorhombic structure and modified Fe-O-Fe angles and octahedral tilt. In addition, it promoted a ferromagnetic (FM) order, which was attributed to both the crystal distortion and Dzyaloshinskii-Moriya interaction. For doped samples, an increase in real permittivity values was observed, and reduced with the increase of frequency. This in good agreement with the Maxwell-Wagner effect