Examinando por Autor "Laughlin, D. E."

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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
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.