Adam Wise

Increased induction in FeCo-based nanocomposite materials with reduced early transition metal growth inhibitors

We report on new high-saturation induction, high-temperature nanocomposite alloys with reduced glass formers. The amounts of the magnetic transition metals and early transition metal growth inhibitors were systematically varied to determine trade-offs between higher inductions and fine microstructures with consequently lower magnetic losses. Alloys of nominal composition (Fe65Co35)79.5+xNb4−xB13Si2Cu1.5 (x=0–4) were cast into a 28 mm wide, 20 μm thick ribbon from which toroidal cores were wound. Inductions and magnetic losses were measured after nanocrystallization and stress relief. We report technical magnetic properties: permeability, maximum induction, remanence ratio, coercive field, and high frequency magnetic losses as a function of composition and annealing temperature for these alloys. Of note is the development of maximum inductions in excess of 1.76 T in cores made of alloys with the x=4 composition and maximum inductions in excess of 1.67 T in alloys with the x=3 composition, which also exhibi...

M-type barium hexaferrite synthesis and characterization for phase shifter applications

M-type barium hexaferrite films have been grown by liquid phase epitaxy and examined by x-ray diffraction, scanning electron microscopy, atomic force microscopy, and conventional and Lorentz-mode transmission electron microscopy (TEM). These films exhibit a diamond chevron shaped “brick wall” microstructure with c-axis oriented hexaferrite platelets. The films are oriented with their c axes in-plane, and parallel to the M-plane sapphire substrate, and exhibit a 30° rotation about the c axis with respect to the substrate. Rocking curves showed (20−20) and (22−40) FWHM values of 1.09° and 1.56°, respectively, for the thinner of two samples, and 0.31° and 0.50° for the thicker sample. The magnetic domain structures have been characterized by Lorentz-mode TEM and the domain walls were found to be pinned to small angle tilt boundaries. Using the measured rocking curve values, the effect of the overall crystalline misorientation on the dispersion of the magnetocrystalline anisotropy of the samples is estimated ...

Phase Evolution in the Fe

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 Fe2TiO4-Fe3O4 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% Fe2TiO4 compounds (balance Fe3O4) 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.

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(Fe50Co50)97V2Nb1 nanoparticles were synthesized in an induction plasma torch and oxidized isochronally at temperatures between room temperature (RT) and 900 °C. The particles exhibited three stages of oxidation present at different temperatures. The initial oxide layer was nearly Co-free, beginning at 3 nm at RT, and Co appeared to oxidize separately from the iron. Iron cations were determined to be the mobile species during oxidation, yielding a progressively more Co-rich core as oxidation progressed, decreasing from an average diameter of 42 to 25 nm, while the oxide tripled in size. At 350 °C, the particles exhibited a less dense core, and at 900 °C the particles were observed to have changed morphology completely with some sintering, forming completely oxidized particles with an average diameter three times the as received size.

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In this work we present preliminary results on magnetization and remanence of synthetic pseudo-binary x(Fe2TiO4)-(1-x)(Fe3O4)(0.30 <; x <; 1.00). Magnetic characterization was performed at temperature ranges from 100 K up to 400 K. The final objective is to characterize the magnetic response as a function of temperature in order to foresight the future magnetic measurements of the magnetometer included into Met-Net mission to Mars. Samples present ferromagnetic behavior with Neel temperatures above the minimum Martian temperature. An increased remanence for sample with x=0.65 has been measured possibly originated by pinning mechanism which might offer a partial explanation as to the crustal magnetism of Mars.

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Processes for making well ordered L10 FePt thin films with root-mean-square surface roughness close to 0.4 nm, perpendicular anisotropy greater than 5 kOe and perpendicular squareness near 1 using a deposition temperature of 390 °C have been developed. In this study, we focused on reducing the ordering temperature and smoothness of L10 FePt films, while achieving good perpendicular magnetic properties by using MgO/CrRu/TiN or MgO/CrRu/Pt seed layers on Si/SiO2 substrates. It was found that the chemical ordering of L10 FePt films is strongly affected by the insertion of a sputtered MgO seed layer, and the CrRu (002) texture on a (002) textured MgO seed layer is substantially improved at high DC power. In order to prevent Cr diffusion, TiN and Pt films were inserted between the CrRu and FePt films. It was found that the smoothness, L10 FePt ordering, and perpendicular magnetic properties were strongly improved by the TiN barrier layer compared to the Pt barrier layer. Increased TiN thickness improved the pe...

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We have synthesized the antiferromagnetic mineral ulvospinel, Fe2TiO4, 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.