Diseño de un magnetómetro de muestra vibrante (VSM) biaxial compacto y de bajo costo

Se presenta el diseño de un magnetómetro de muestra vibrante (VSM) de bajo costo, para medidas de ciclos de histéresis a temperatura ambiente, en un campo máximo de 0.3 T. El conjunto es un sistema compacto, controlado mediante una PC, que permite medir la magnetización en forma biaxial intercambiando el conexionado de las bobinas sensoras. El límite de sensibilidad del equipo se encuentra por debajo de 0.1 emu. Se muestran ciclos de histéresis obtenidos para diferentes muestras ferromagnéticas.In this work, the design and construction of a biaxial and low-cost vibrating sample magnetometer (VSM) are introduced. This VSM is automated and works at room temperature , with a 0,3 T as maximum applied field. As pick-up coils, were employed the static poles of the driver motor of a 5 1/4” disk. Sensitivity is below 0,1 emu. Different hysteresis cycles measured for different samples in parallel and perpendicular applied field, are shown.Fil: Saccone, Fabio Daniel. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Preparación y estudio de ferromagnetos duros : Aplicaciones a los imanes permanentes

Facultad de Ciencias Exacta

Заселенность 4d-состояний в Mo, Nb на основании анализа тонкой структуры рентгеновских спектров поглощения сплавов Nd-Fe-B-T (T: Mo, Nb) вблизи границы l3,2

Samples of NdyFe(86–-y–x)B14Tx (T: Mo, Nb; x = 2, 4; y = 7, 8) alloys were studied by X-ray absorption spectroscopy. The NEXAFS spectra of NdFeB ribbons produced by the melt spinning technique (as quenched, AQ) and subsequently annealed (TT) were taken at Mo and Nb L3,2-edge. We calculated the variations in occupancy of the 4d-states (in both additives), finding an opposite trend in their filling. The most significant changes were observed in the T2Nd7 system, for which the electron occupancy in the 4d levels was modified to an excess of 1 electron/atom (after thermal treatment). The correlation between these results and magnetic features of the alloys are evidenced.Сплавы NdyFe(86-y-x)B14Tx (T: Mo, Nb; x = 2, 4; y =7, 8) изучены методом рентгеновской абсорбционной спектроскопии. Образцы имели форму полосок, полученных методом вытягивания из расплава (в состоя- нии после закалки), а затем отожженных. Тонкая структура рентгеновских спектров поглощения спла- вов NdFeB исследована вблизи границы L3,2 Мо и Nb. Рассчитаны изменения заселенности 4d-состояний (в обеих примесях) и обнаружены противоположные тенденции в их заполнении. Наиболее существенные изменения наблюдались в системе T2Nd7, где заселенность 4d-уровня изменялась более чем на 1 элект- рон/атом (после термообработки). Корреляция между этими результатами и магнитными характерис- тиками исследованных сплавов очевиднаFil: Bilovol, Vitaliy. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Saccone, Fabio Daniel. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Structural and magnetic properties of multilayered TiO2/FM/ TiO2/FM/CoFe2O4 (FM: Fe or Py) films grown by pulsed laser deposition

Two types of multilayered thin films of structure TiO2/FM/ TiO2/FM/CoFe2O4 with FM = Fe or Py were grown by means of the pulsed layer deposition technique with a total thickness of less than 350 nm. Their structural properties were analyzed by X-ray diffraction and the Fe K-edge absorption was measured by X-ray fluorescence in grazing incidence geometry. By means of near edge absorption X-ray spectroscopy (XANES), we retrieved information about the octahedral Fe+3 environment within the cobalt ferrite (CoFe2O4) films as well as the role of titanium oxide (TiO2) as a good protective layer for these multilayered systems. The bulk magnetic properties of both samples exhibit certain similarities: at 10 K, the coercive field of their hysteresis loops is enhanced to approximately 1 T, with an intermediate magnetization drop occurring at approximately 2000 Oe reverse field strength, indicating the separated magnetization reversal behavior of pinned and unpinned grains within the FM layers. In contrast to this low temperature field dependence, the collective magnetic behavior is gradual upon field inversion when hysteresis loops are measured at or near room temperature. By using the FORC diagram technique at room temperature, we investigated this gradual transition in more detail and identified clear differences in between the two FM layer materials.Fil: Saccone, Fabio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; ArgentinaFil: Vavassori, Paolo. CIC NanoGUNE; EspañaFil: Berger, Andreas. CIC NanoGUNE; España. Basque Foundation for Science; Españ

Study on target-film structural correlation in thin cobalt ferrite films grown by Pulsed Laser Deposition technique

We prepared three films of crystalline cobalt ferrite under identical deposition conditions (time, temperature, pressure) using three different targets consolidated from CoFe2O4 (CFO) crystalline nanoparticles (NPs). The NPs were previously prepared by a chemical route varying their synthesis conditions in order to promote different variations in the degree of structural distortions. The purpose of this work is to study how the degree of crystal distortion of the precursor material (target) influences the structural properties of the films when they are grown by pulsed laser deposition (PLD). 57Fe Mössbauer spectroscopy was used to study the local environment of iron atoms in the powders (targets for PLD). The Williamson–Hall plots were used to show the degree of the strain present in the films. X-ray absorption near edge structure spectra of the films, taken in grazing incidence geometry, were also carried out. The results explicitly demonstrate that the film with the largest strain was deposited using structurally more imperfect CFO powders whereas the film with the smallest strain was grown using the best powder from the structural point of view. These results were reinforced indirectly by magnetic measurements (exchange bias effect) in Fe/CFO bilayers (thin iron film was deposited additionally for this purpose) when hysteresis loops were analyzed after field cooling at a 3 T magnetic field. We show that the quality of thin cobalt ferrite films depends on the quality of the precursor material when the PLD technique is involved.Fil: Bilovol, Vitaliy. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; Argentina; Argentina. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; ArgentinaFil: Pampillo, L. G.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; Argentina; Argentina. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; ArgentinaFil: Saccone, Fabio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; Argentina; Argentina. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; Argentin

Structural and magnetic properties of Zn doped magnetite nanoparticles obtained by wet chemical method

The structural and magnetic properties of Fe(3-x)ZnxO4(x: 0, 0.1, 0.2, 0.5, 1) nanoparticles, prepared by wet chemical method, have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), Mössbauer spectroscopy, and magnetization measurements. The nanoparticles are polyhedrical-shaped with a narrow distribution in size as it was verified by SEM. By Rietveld analysis of XRD patterns, it was determined that the crystallites' sizes of Fe(3-x)ZnxO4 in spinel structure is in the range of 30 to 50 nm. Hysteresis cycles, measured at different temperatures (300, 200, 100, 50, and 7 K), showed an increase in saturation, while temperature is diminished, as it is expected. All the samples, exhibited a high blocking temperature of ~350 K, as it was determined by zero field cooling-field cooling measurements. This fact, reveals their strongly interacting superparamagnetic nature. Real ac susceptibility increases with temperature, while the imaginary part has a maximum, which depends on frequency, and it is related to a critical temperature, which depends on composition. A Néel-Arrhenius dependence of frequency on the critical temperature was found for all the samples. We determined a minimum of the effective anisotropy for x=0.2.Fil: Sergio Ferrari. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; Argentina; ArgentinaFil: Saccone, Fabio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; Argentina; ArgentinaFil: Aphesteguy, Juan Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; Argentina; Argentin

XANES and XPS study of electronic structure of Ti-enriched Nd–Fe–B ribbons

Electronic structure of rapidly quenched ribbons of nominal composition NdyFe(86-y-x)B14Tix (x= 0, 2, 4; y= 7, 8 at.%) was studied by X-ray absorption (Fe and Ti K-edge) and X-ray photoelectron spectroscopy. It was found by XANES that Ti addition promotes modifications of the electronic structure of Fe sub-band. From the analysis of differences in the pre-edges structure areas, coming from variations in the 3d density of states near the Fermi level, the evidences of acceptor nature of Ti and Fe atoms in NdFeB alloys are present. Using photoelectron spectroscopy, we found that neodymium, iron and titanium are in both, metallic and oxidized, states on the surface of the ribbons. A higher Ti0 content (at high vacuum) is characteristic of the annealed samples. The presence of oxidized titanium states was corroborated by XANES.Fil: Bilovol, Vitaliy. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; ArgentinaFil: Ferrari, Sergio. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; ArgentinaFil: Derewnicka, D.. Institute of Precision Mechanics; PoloniaFil: Saccone, Fabio Daniel. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; Argentin

Magnetic anisotropy induced in Nd16Fe76B8 by Hf additions

Remanence, coercivity and maximum energy product (BH)max of Nd16Fe76-xHfxB8 (x = 0, 0.1, 0.2) magnets processed under different hydrogenation-disproportionation-desorption-recombination (HDDR) conditions, were studied. Vibrating sample magnetometry results showed that Hf-doped materials develop an important degree of anisotropy, especially for the case of solid-HDDR treatments at 800°C and 850°C, with the largest effect at 850°C. Maximum values of remanence and coercivity were observed for Hf-added samples S-HD at 850°C, and 900°C, respectively. The highest (BH)max value was also observed in S-HD 900°C Hf-added samples. These results are discussed in terms of the expected microstructure of the intermediate HD and final HDDR processed powders. © 2002 Elsevier Science B.V. All rights reserved.Fil: Rodríguez Torres, C. E.. Facultad de Ciencias Exactas, Universidad Nacional de la Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Saccone, Fabio Daniel. Facultad de Ciencias Exactas, Universidad Nacional de la Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Sánchez, Francisco Homero. Facultad de Ciencias Exactas, Universidad Nacional de la Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentin