Examinando por Autor "McHenry, M. E."

Mostrando 1 - 8 de 8

Acceso Abierto
Data Base of Extraterrestrial Magnetic Minerals, Test and Magnetic Simulation
(Institute of Electrical and Electronics Engineers, 2013-07-15) Fernández, A. B.; McHenry, M. E.; Díaz Michelena, M.; Aroca, C.; Maicas, M.
The description of the planetary magnetic anomalies is a difficult task that combines either aeromagnetic or in-situ magnetic field measurements, and further laboratory characterization of the local rocks. In the case of extraterrestrial planets this is a very difficult and costly task. With the objective to develop predictive algorithms prior to in-situ measurements, two complimentary lines of work have been undertaken: 1) characterization of magnetic minerals which occur in great abundance in extraterrestrial crusts; and 2) development of finite element method models (FEM) using the properties of these minerals to model possible scenarios and the variation of their magnetic behavior with temperature and temperature gradient swings on the superficial layers of the planets. The ultimate objective is the future comparison between the measurements developed by instruments on board Martian landers and rovers and the developed models.
Restringido
Fabrication of thin films for a small alternating gradient field magnetometer for biomedical magnetic sensing applications
(AIP Publishing, 2011-03-23) Jones, N. J.; McNerny, K. L.; Sokalski, V.; Díaz Michelena, M.; Laughlin, D. E.; McHenry, M. E.; National Science Foundation (NSF)
Thin film alternating gradient field magnetometers (AGFM) have potential for measuring magnetic moments of minerals in extraterrestrial soil samples. AGFM sensors offer increased spatial resolution required to detect magnetic nanoparticles for biosensing applications. We have fabricated a patterned thin film with the properties necessary for use in a small AGFM system. Hexagonal-close-packed CoCrPt thin films of 20 and 500 nm were sputtered (nominal composition of Co66Cr15Pt19), showing a high magnetic moment and large out-of-plane anisotropy. The films showed a Δθ50 of better than 3° for the (002) CoCrPt peak for all films, which improves with thickness. The texture is partly due to the NiW and Ru underlayers. The films showed an out-of-plane easy axis, indicating a strong uniaxial anisotropy that exceeds the shape demagnetization energy. This is due to the addition of Cr, which decreases the magnetic moment of the films; magnetoelastic coupling and film stresses may also aid in achieving a perpendicular anisotropy. The first-order uniaxial anisotropy constants were calculated as a function of temperature, ranging from 3.7 × 106 ergs/cm3 at room temperature to 6.8 × 105 ergs/cm3 at 500 °C, and the T dependence agrees with Akulov’s theory for uniaxial materials. The thickest film was etched with a checkerboard pattern to decrease the demagnetization effects, which are seen more influentially in the thicker films. This opened up the hysteresis loop, and decreased the amount of field necessary to overcome the thin film geometry.
Acceso Abierto
Phase Evolution in the Fe-3 O-4 -Fe-2 TiO4 Pseudo-Binary System and Its Implications for Remanent Magnetization in Martian Minerals
(Institute of Electrical and Electronics Engineers, 2011-09-26) Wise, A.; Saenko, M.; Velazquez, A. M.; Laughlin, D. E.; Díaz Michelena, M.; McHenry, M. E.; National Science Foundation (NSF)
Titanomagnetites offer a rich system to explore the role of fine microstructure on magnetic properties. They are important minerals in basalts, and are commonly found on the moon and Mars. Here magnetic measurements were used to monitor decomposition and phase evolution in the pseudo-binary Fe 2 TiO 4 -Fe 3 O 4 solid solution system. The phases appearing in the decomposition are a strongly magnetic magnetite and a weakly magnetic Ti-rich spinel. For the 40, 50, and 60 at% Fe 2 TiO 4 compounds (balance Fe 3 O 4 ) explored here, a metastable solid solution is nonmagnetic at temperatures where decomposition kinetics can be monitored in reasonable experimental times. The magnetization of magnetite formed by the decomposition offers a direct measure of the volume fraction transformed. Time-dependent magnetization measurements were used to monitor the kinetics of decomposition and compared to models for spinodal decomposition and nucleation and growth kinetics for compositions outside the spinodes. The fine microstructure resulting from spinodal decomposition and exchange bias mechanisms for coupling, may be important in understanding the remnant state of these minerals on Mars
Restringido
Phase Identification and Temperature-Dependent Magnetization of Ti-Rich Titanomagnetite (0.5 <= x <= 1) in Different Atmospheres
(Institute of Electrical and Electronics Engineers, 2013-07-15) Lan, S.; Groschner, C.; Runco, J. N.; Wise, A.; Díaz Michelena, M.; Laughlin, D.; McHenry, M. E.
Reduced titanomagnetite solid solutions, xFe 2 TiO 4 - (1 - x)Fe 3 O 4 , with 0.5 ≤ × ≤ 1, were synthesized by sintering in 99.996% pure flowing argon. Samples showed a systematic variation in the second phase amount as a function of x. A wustite second phase primarily forms near the surface of titanomagnetite pellets. The amount of wustite decreases with increasing Ti concentration. XRD data confirms that samples with x > 0.8 have less than 1% wustite. M(T) curves were measured by vibrating sample magnetometer (VSM). A magnetization hump is observed in M(T) during heating and explained by ferrimagnetic phases formed by exsolution and precipitation processes. These phases were identified as titanomaghemite and magnetite by fitting M(T) cooling curves with a multi-phase Brillouin function.
Acceso Abierto
Single Point Gradiometer for Planetary Applications
(Institute of Electrical and Electronics Engineers, 2015-03-09) Mesa, J. L.; Díaz Michelena, M.; Ciudad, D.; Schoenthal, W.; McHenry, M. E.; Maicas, M.; Aroca, C.; Ministerio de Ciencia e Innovación (MICINN)
We have designed and fabricated a microelectromechanical device, based on the alternating field gradient concept, to measure surface magnetic field gradient on planets. Its sensitivity is 4 10 -4 T/m, which is appropriate for magnetite outcrops and areas with rocks formed at different stages recording geomagnetic field reversals. We present the results obtained with three different prototypes.
Restringido
Studies on Structural, Magnetic and Thermal Properties of xFe2TiO4-(1−x)Fe3O4 (0≤x≤1) Pseudo-binary System
(Elsevier, 2012-04-12) Sorescu, M.; Xu, T.; Wise, A.; Díaz Michelena, M.; McHenry, M. E.; National Science Foundation (NSF)
The xFe2TiO4-(1−x)Fe3O4 pseudo-binary systems (0≤x≤1) of ulvöspinel component were synthesized by solid-state reaction between ulvöspinel Fe2TiO4 precursors and commercial Fe3O4 powders in stochiometric proportions. Crystalline structures were determined by X-ray powder diffraction (XRD) and it was found that the as-obtained titanomagnetites maintain an inverse spinel structure. The lattice parameter a of synthesized titanomagnetite increases linearly with the increase in the ulvöspinel component. 57Fe room temperature Mössbauer spectra were employed to evaluate the magnetic properties and cation distribution. The hyperfine magnetic field is observed to decrease with increasing Fe2TiO4 component. The fraction of Fe2+ in both tetrahedral and octahedral sites increases with the increase in Ti4+ content, due to the substitution and reduction of Fe3+ by Ti4+ that maintains the charge balance in the spinel structure. For x in the range of 0 ≤x≤0.4, the solid solution is ferrimagnetic at room temperature. However, it shows weak ferrimagnetic and paramagnetic behavior for x in the range of 0.40.70, it only shows paramagnetic behavior, with the appearance of quadrupole doublets in the Mössbauer spectra. Simultaneous differential scanning calorimetry and thermogravimetric analysis (DSC–TGA) studies showed that magnetite is not stable, and thermal decomposition of magnetite occurs with weight losses accompanying with exothermic processes under heat treatment in inert atmosphere.
Restringido
Synthesis and magnetic properties of single phase titanomagnetites
(AIP Publishing, 2014-03-11) Schoenthal, W.; Liu, X.; Cox, T.; Mesa, J. L.; Maícas, N.; Díaz Michelena, M.; Laughlin, D. E.; McHenry, M. E.
The focus of this paper is the study of cation distributions and resulting magnetizations in titanomagnetites (TMs), (1−x)Fe3O4−xFe2TiO4 solid solutions. TM remnant states are hypothesized to contribute to planetary magnetic field anomalies. This work correlates experimental data with proposed models for the TM pseudobinary. Improved synthesis procedures are reported for single phase Ulvöspinel (Fe2TiO4), and TM solid solutions were made using solid state synthesis techniques. X-ray diffraction and scanning electron microscopy show samples to be single phase solid solutions. M-H curves of TM75, 80, 85, 90, and 95 (TMX where X = at. % of ulvöspinel) were measured using a Physical Property Measurement System at 10 K, in fields of 0 to 8 T. The saturation magnetization was found to be close to that predicted by the Neel model for cation distribution in TMs. M-T curves of the remnant magnetization were measured from 10 K to 350 K. The remnant magnetization was acquired at 10 K by applying an 8 T field and then releasing the field. Experimental Neel temperatures are reported for samples in the Neel model ground state.
Restringido
The Role of Atmosphere on Phase Transformations and Magnetic Properties of Ulvospinel
(Institute of Electrical and Electronics Engineers, 2013-07-12) Groschner, C.; Lan, S.; Wise, A.; Leary, A.; Lucas, M. S.; Park, C.; Laughlin, D. E.; Díaz Michelena, M.; McHenry, M. E.; National Science Foundation (NSF)
We have synthesized the antiferromagnetic mineral ulvospinel, Fe 2 TiO 4, in Ar to assess the role of inert atmosphere on phase formation and magnetic properties. We report the role of atmosphere on a possible phase transition and the magnetic properties of this mineral. Atmosphere dependent transformations of ulvospinel are observed with increasing temperature. Oxidation of ulvospinel to form metastable titanomaghemite is shown to occur at 300° in atmospheric conditions. Only slight titanomaghematitzation was observed in samples transformed under pressure in in situ temperature dependent X-ray experiments. Formation of ilmenite and hematite from ulvospinel was observed under high temperature, high pressure, and low oxygen atmosphere conditions.