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122 results on '"Soulen, R. J."'

8. Measurement of the transport spin polarization of doped strontium ruthenates using point contact Andreev reflection.

Author

Woods, G. T., Sanders, J., Kolesnik, S., Maxwell, T., Srikanth, H., Dabrowski, B., Osofsky, M. S., and Soulen, R. J.

Subjects
STRONTIUM compounds, RUTHENIUM compounds, RUTHENIUM oxide superconductors, ELECTRIC conductivity, POLARIZATION (Electricity), FERROMAGNETIC materials
Abstract

Electrical conductivity, magnetic susceptibility, and point contact Andreev reflection (PCAR) studies were done on bulk, polycrystalline SrRu1-x(TM)xO3 (TM=Cr, Mn, Ti) and SrRu0.92O3 with a high degree of disorder. Fits of the temperature dependence of the latter using the Curie–Weiss law yielded values for the Curie–Weiss temperature, Θ. Furthermore, the values of the Curie temperature, TC were identified by determining the maximum susceptibility as a function of temperature. PCAR measurements were done to determine the transport spin polarization, Pt (0≤Pt≤1.0). Pure SrRuO3 undergoes ferromagnetic ordering at a Curie temperature of TC∼160 K and has a relatively high spin polarization (∼0.6). Our results indicate that when the lattice is disordered from either the presence of Ru lattice site defects or the substitution of a transition metal for the Ru, TC changes by a factor of 2, and Θ by a factor of 1.7. By contrast, the spin polarization is unchanged for both SrRu0.94Ti0.06O3 and SrRu0.9Mn0.1O3, while it is barely changed (P=0.5) for SrRu0.9Cr0.1O3. [ABSTRACT FROM AUTHOR]

Published
2008
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12. Growth and magnetic properties of single crystal Fe[sub 1-x]Co[sub x]S[sub 2] (x=0.35–1).

Author

Cheng, S. F., Woods, G. T., Bussmann, K., Mazin, I. I., Soulen, R. J., Carpenter, E. E., Das, B. N., and Lubitz, P.

Subjects
CONSTITUTION of matter, CRYSTALS, ELECTRON microscopy, THERMOMAGNETISM
Abstract

The pyrite Fe[SUB1-x]Co[SUBX]S[SUB2] (0.25≤x≤0.9) was predicted to be half metal, insensitive to Fe-Co disorder. To verify its half metallicity, we have grown single crystals of Fe[SUB1-x]Co[SUBx]S[SUB2] (x)=0.35, 0.5, 0.75, 0.9, and 1). Crystals of up to a few mm in size by temperature gradient (923-873 K) solution growth from Te melts, which showed high crystalline quality by scanning electron microscopy, x-ray diffraction, and magnetic measurements. A half-metallic magnetization of 1±0.03μ[SUBB] per Co atom was found for x=0.35-0.9. Point contact Andreev reflection measurements, however, showed spin polarization of 47%-61% with the maximum around x=0.5, well below predictions. Ferromagnetic resonance measurements give g∼2.08 with large intrinsic damping, which indicates a reduced half-metallicity. Inductively coupled plasma and energy dispersive x-ray spectroscopy results confirm a sulfur deficiency of &sim1.5%-10% [Fe,Co)S[SUB2-y],0.03≤y≤0.2] and small amounts of Te. Electronic structure calculations show the extra electron provided by Co substitution to FeS[SUB2] populates a sulfur-derived conduction band. Consequently, S deficiency and/or S site disorder are expected to affect the transport properties. This is consistent with the low polarization measurements and again indicates the importance of crystalline order in obtaining highly spin-polarized materials. [ABSTRACT FROM AUTHOR]

Published
2003
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13. Ferromagnetic resonance observation of exchange and relaxation effects in CrO[sub 2].

Author

Lubitz, P., Rubinstein, M., Osofsky, M. S., Nadgorny, B. E., Soulen, R. J., Bussmann, K. M., and Gupta, A.

Subjects
MAGNETIC properties of thin films, FERROMAGNETIC resonance
Abstract

Ferromagnetic resonance (FMR) was observed in epitaxial thin films of CrO[sub 2] grown on TiO[sub 2]. FMR spectra were taken at 9.5 and 35 GHz and at temperatures from 4 K to above the ordering temperature of 393 K. The spectra of these films are generally complicated because of surface roughness and the distribution of stresses and anisotropies through their thickness. The thinnest films, however, display typical spin wave spectra, which could be approximated using uniform magnetic material analyses. The exchange constant at 300 K, D∼70 meV Å[sup 2], is consistent with values derived from the temperature dependence of M at low temperatures. The temperature dependence of D was extracted from the spin wave spacing and is similar to other magnetic metals. Our data indicate a room temperature Gilbert damping parameter of at most 0.0023 near 300 K, which is less than those of metallic magnetic materials except possibly Fe. The small damping parameter suggests that! intrinsic losses seen in other magnetic metals, which may arise from electronic transitions between bands of different spin character, are small in CrO[sub 2]. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2001
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16. Evidence for High-Temperature Superconductivity in Doped Laser-Processed Sr-Ru-O

Author

Gulian, A. M., Wood, K. S., Van Vechten, D., Claassen, J., Soulen, R. J., Qadri, S., Osofsky, M., Lucarelli, A., Luepke, G., Badalyan, G. R., Kuzanyan, V. S., Kuzanyan, A. S., and Nikoghosyan, V. R.

Subjects
Superconductivity (cond-mat.supr-con), Condensed Matter - Superconductivity, FOS: Physical sciences
Abstract

We have discovered that samples of a new material produced by special processing of crystals of Sr2RuO4 (which is known to be a triplet superconductor with Tc values ~1.0-1.5K) exhibit signatures of superconductivity (zero DC resistance and expulsion of magnetic flux) at temperatures exceeding 200K. The special processing includes deposition of a silver coating and laser micromachining; Ag doping and enhanced oxygen are observed in the resultant surface layer. The transition, whether measured resistively or by magnetic field expulsion, is broad. When the transition is registered by resistive methods, the critical temperature is markedly reduced when the measuring current is increased. The resistance disappears by about 190K. The highest value of Tc registered by magneto-optical visualization is about 220K and even higher values (up to 250K) are indicated from the SQUID-magnetometer measurements.

Published
2005

19. The origin of high transport spin polarization in La$_{0.7}$Sr$_{0.3} $MnO$_{3}$: direct evidence for minority spin states

Author

Nadgorny, B., Mazin, I. I., Osofsky, M., Soulen, R. J., Broussard, P., Stroud, R. M., Singh, D. J., Harris, V. G., Arsenov, A., and Mukovskii, Ya.

Subjects
Condensed Matter::Materials Science, Condensed Matter - Materials Science, Condensed Matter - Strongly Correlated Electrons, Strongly Correlated Electrons (cond-mat.str-el), Materials Science (cond-mat.mtrl-sci), FOS: Physical sciences, Condensed Matter::Strongly Correlated Electrons
Abstract

Using the point contact Andreev reflection technique, we have carried out a systematic study of the spin polarization in the colossal magnetoresistive manganite, La$_{0.7}$Sr$_{0.3}$MnO$_{3}$} (LSMO). Surprisingly, we observed a significant increase in the current spin polarization with the residual resistivity. This counterintuitive trend can be understood as a transition from ballistic to diffusive transport in the contact. Our results strongly suggest that LSMO does have minority spin states at the Fermi level. However, since its current spin polarization is much higher than that of the density of states, this material can mimic the behavior of a true half-metal in transport experiments. Based on our results we call this material a {\it transport} half-metal., 6 pages, revtex, epsfigs embedded (two color figs)

Published
2000

20. High Temperature Superconductors for Naval Power Applications

Author

NAVAL RESEARCH LAB WASHINGTON DC, Holtz, R. L., Soulen, R. J., Osofsky, M., Claassen, J. H., Spanos, G., Gubser, D. U., Goswami, R., Patten, M., NAVAL RESEARCH LAB WASHINGTON DC, Holtz, R. L., Soulen, R. J., Osofsky, M., Claassen, J. H., Spanos, G., Gubser, D. U., Goswami, R., and Patten, M.

Abstract

As the Navy moves to the all-electric warship, superconducting materials will play a key enabling role. High temperature superconducting (HTS) motors and generators will enable extended range, high-efficiency, high-power density naval propulsion, and compact generators for weapons and ship systems. Compact mobile HTS generators also may provide portable/mobile power for littoral and expeditionary operation, naval air, and homeland security. The "second generation" high-temperature superconductors (2G-HTS) based on yttrium-bariumcopper- oxide (YBCO) "coated conductor" architectures are undergoing a processing technology breakthrough that will lead to large-scale manufacture by 2008. NRL is working with manufacturers to address key issues in the processing and performance of these conductors during this fast-paced stage of technology development. In particular, 2G-HTS process development is accelerated by fundamental understanding of the materials microstructures gained at NRL. Key goals include reduction of AC losses in the HTS motors and generators, as well as novel inductor designs for power electronics. Ensuring superior fatigue properties of the HTS materials compatible with the lifecycle of naval machinery is a key objective., Published in NRL Review, Materials Science and Technology, 2006.

Published
2006

21. Measurements of AC Loss In Second-Generation HTS Tapes in a DC Magnetic Field

Author

Osofsky, M. S., primary, Soulen, R. J., additional, Gubser, D. U., additional, Datta, T., additional, Balachandran, U. (Balu), additional, Amm, Kathleen, additional, Evans, David, additional, Gregory, Eric, additional, Lee, Peter, additional, Osofsky, Mike, additional, Pamidi, Sastry, additional, Park, Chan, additional, Wu, Judy, additional, and Sumption, Mike, additional

Published
2008
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28. The Provisional Low Temperature Scale from 0.9 mK to 1 K, PLTS-2000.

Author

Rusby, R. L., Durieux, M., Reesink, A. L., Hudson, R. P., Schuster, G., Kühne, M., Fogle, W. E., Soulen, R. J., and Adams, E. D.

Subjects
INTERNATIONAL temperature scale, TEMPERATURE measurements, LOW temperatures, MELTING points
Abstract

The Provisional Low Temperature Scale from 0.9 mK to 1 K, PLTS-2000, was adopted by the Comité International des Poids et Mesures in October 2000. It is defined using an equation for the melting pressure of 3He over the complete temperature range, and forms an extension of the International Temperature Scale of 1990, ITS-90, below its lower limit of 0.65 K. An internationally-accepted ultra-low temperature scale is needed to provide the basis for reliable thermometry in the temperature range in which commercial dilution refrigerators operate, and at lower temperatures where experiments investigating the thermodynamic properties of 3He and other condensed matter are carried out in many research centres. This paper is a summary of a fuller publication describing the background and derivation of the scale, published in the Journal of Low Temperature Physics [1], and includes tables of values of melting pressure, pm / MPa, and temperature T2000 / K, and the derivative, dpm /dT2000 in MPa/K. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2003
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35. Measurement of the spin polarization of LaSrMnO

Author

Osofsky, M. S., primary, Nadgorny, B., additional, Soulen, R. J., additional, Broussard, P., additional, Rubinstein, M., additional, Byers, J., additional, Laprade, G., additional, Mukovskii, Y. M., additional, Shulyatev, D., additional, and Arsenov, A., additional

Published
1999
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36. Suppression of superconductivity by injection of spin-polarized current

Author

Koller, Daniel, primary, Osofsky, M. S., additional, Chrisey, D. B., additional, Horwitz, J. S., additional, Soulen, R. J., additional, Stroud, R. M., additional, Eddy, C. R., additional, Kim, J., additional, Auyeung, R. C. Y., additional, Byers, J. M., additional, Woodfield, B. F., additional, Daly, G. M., additional, Clinton, T. W., additional, and Johnson, Mark, additional

Published
1998
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41. Superconductivity above 100 K in compounds containing Hg

Author

Osofsky, M. S., primary, Lechter, W. L., additional, Toth, L. E., additional, Skelton, E. F., additional, Drews, A. R., additional, Kim, C. C., additional, Das, B., additional, Qadri, S. B., additional, Webb, A. W., additional, and Soulen, R. J., additional

Published
1995
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45. Erratum ‘‘Anomalous temperature dependence of the upper critical magnetic field in Bi-Sr-Cu-O’’ [Phys. Rev. Lett.71, 2315 (1993)]

Author

Osofsky, M. s., primary, Soulen, R. J., additional, Wolf, S. A., additional, Broto, J. M., additional, Rakoto, H., additional, Ousset, J. C., additional, Coffe, G., additional, Askenazy, S., additional, Pari, P., additional, Bozovi, I., additional, Eckstein, J. N., additional, and Virshup, G. F., additional

Published
1994
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46. Measurements ofH c2(T) in Bi-Sr-Cu-O

Author

Osofsky, M. S., primary, Soulen, R. J., additional, Wolf, S. A., additional, Broto, J. M., additional, Rakoto, H., additional, Ousset, J. C., additional, Coffe, G., additional, Askenazy, S., additional, Pari, P., additional, Bozovic, I., additional, Eckstein, J. N., additional, and Virshup, G. F., additional

Published
1994
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