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505 results on '"Barmak, K."'

4. Measurement of spin mixing conductance in Ni$_{81}$Fe$_{19}$/$\alpha$-W and Ni$_{81}$Fe$_{19}$/$\beta$-W heterostrucutures via ferromagnetic resonance

Author

Cao, W., Liu, J., Zangiabadi, A., Barmak, K., and Bailey, W. E.

Subjects
Condensed Matter - Materials Science
Abstract

We present measurements of interfacial Gilbert damping due to the spin pumping effect in Ni$_{81}$Fe$_{19}$/W heterostructures. Measurements were compared for heterostructures in which the crystallographic phase of W, either $\alpha$(bcc)-W or $\beta$(A15)-W, was enriched through deposition conditions and characterized using X-ray diffraction (XRD) and high-resolution cross-sectional transmission electron microscopy (HR-XTEM). Single phase Ni$_{81}$Fe$_{19}$/$\alpha$-W heterostructures could be realized, but heterostructures with $\beta$-W were realized as mixed $\alpha$-$\beta$ phase. The spin mixing conductances (SMC) for W at interfaces with Ni$_{81}$Fe$_{19}$ were found to be significantly lower than those for similarly heavy metals such as Pd and Pt, but comparable to those for Ta, and independent of enrichment in the $\beta$ phase.

Published
2019
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5. Hundredfold Enhancement of Light Emission via Defect Control in Monolayer Transition-Metal Dichalcogenides

Author

Edelberg, D., Rhodes, D., Kerelsky, A., Kim, B., Wang, J., Zangiabadi, A., Kim, C., Abhinandan, A., Ardelean, J., Scully, M., Scullion, D., Embon, L., Zhang, I., Zu, R., Santos, Elton J. G., Balicas, L., Marianetti, C., Barmak, K., Zhu, X. -Y., Hone, J., and Pasupathy, A. N.

Subjects
Condensed Matter - Materials Science
Abstract

Two dimensional (2D) transition-metal dichalcogenide (TMD) based semiconductors have generated intense recent interest due to their novel optical and electronic properties, and potential for applications. In this work, we characterize the atomic and electronic nature of intrinsic point defects found in single crystals of these materials synthesized by two different methods - chemical vapor transport and self-flux growth. Using a combination of scanning tunneling microscopy (STM) and scanning transmission electron microscopy (STEM), we show that the two major intrinsic defects in these materials are metal vacancies and chalcogen antisites. We show that by control of the synthetic conditions, we can reduce the defect concentration from above $10^{13} /cm^2$ to below $10^{11} /cm^2$. Because these point defects act as centers for non-radiative recombination of excitons, this improvement in material quality leads to a hundred-fold increase in the radiative recombination efficiency.

Published
2018
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15. Measurement of spin mixing conductance in Ni81Fe19/α-W and Ni81Fe19/β-W heterostructures via ferromagnetic resonance.

Author

Cao, W., Liu, J., Zangiabadi, A., Barmak, K., and Bailey, W. E.

Subjects
FERROMAGNETIC resonance, HETEROSTRUCTURES, HEAVY metals, TRANSMISSION electron microscopy
Abstract

We present measurements of interfacial Gilbert damping due to the spin pumping effect in Ni 81 Fe 19 / W heterostructures. Measurements were compared for heterostructures in which the crystallographic phase of W, either α (bcc)-W or β (A15)-W, was enriched through deposition conditions and characterized using X-ray diffraction and high-resolution cross-sectional transmission electron microscopy. Single-phase Ni 81 Fe 19 / α -W heterostructures could be realized, but heterostructures with β -W were realized as a mixed α - β phase. The spin mixing conductances for W at interfaces with Ni 81 Fe 19 were found to be significantly lower than those for similar heavy metals such as Pd and Pt, but comparable to those for Ta, and independent of enrichment in the β phase. [ABSTRACT FROM AUTHOR]

Published
2019
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16. Contributor contact details

Author

Barmak, K., primary, Coffey, K.R., additional, Ingham, B., additional, Toney, M.F., additional, Barmak, K., additional, Barna, P.B., additional, Radnóczi, G., additional, Weihs, T.P., additional, Zhang, S.-L., additional, Zhang, Z., additional, Nix, W.D., additional, Thomson, T., additional, Shelton, D., additional, and Schelling, P., additional

Published
2014
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18. A1 to [L1.sub.0] transformation in FePt films with ternary alloying additions of Ag and Au

Author

Wang, B., Barmak, K., and Klemmer, T.J.

Subjects
Gold -- Magnetic properties, Gold -- Thermal properties, Gold -- Electric properties, Iron alloys -- Magnetic properties, Iron alloys -- Electric properties, Iron alloys -- Thermal properties, Magnetic recorders and recording -- Analysis, Platinum -- Magnetic properties, Platinum -- Electric properties, Platinum -- Thermal properties, Silver -- Magnetic properties, Silver -- Electric properties, Business, Electronics, Electronics and electrical industries
Published
2010

26. Calorimetric studies of the A1 to Li(sub 0) transformation in binary FePt thin films with compositions in the range of 47.5-54.4 at percentage Fe

Author

Barmak, K., Svedberg, E.B., Kim, J., Howard, J., Berry, D.C., Hanani, W.N., and Wierman, K.

Subjects
Platinum compounds -- Magnetic properties, Dielectric films -- Research, Thin films -- Research, X-rays -- Diffraction, X-rays -- Usage, Physics
Abstract

The use of differential scanning calorimetry in conjunction with x-ray and electron diffraction, to investigate the Al to L1(sub 0) ordering transformation inbinary FePt films with compositions in the range of 47.5-54.4 at. percentage Fe is done. The lattice parameter of the A1 phase and the c/a ratio of the L1(sub 0) phase decrease with the increase in Fe content.

Published
2005

37. On the relationship of high coercivity and L1(sub 0) ordered phase in CoPt and FePt thin films

Author

Ristau, R.A., Barmak, K., Lewis, L.H., Coffey, K.R., and Howard, J.K.

Subjects
Annealing -- Research, Order-disorder models -- Research, Platinum compounds -- Research, Thin films -- Research, Physics
Abstract

Research was conducted to study the microstructure and the room-temperature hysteretic magnetic characteristics of sputtered, 10 nm thin films of equiatomic binary alloys of CoPt and FePt using transmission electron microscopy (TEM) and a superconducting quantum interference device magnetometer. Dark-field TEM images were digitally analyzed to characterize transformation from an atomically disordered, face-centered-cubic structure to the L1(sub 0) ordered structure. It has been concluded that a direct relationship exists between the ordered volume fraction and the coercivity, with the maximum value of the coercivity coinciding with the fully ordered structure.

Published
1999

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