Engineering topics

Ho, P

Publications and source records attributed to Ho, P.

3 records

DOE OSTI2011

(001) textured L1{sub 0}-FePt pseudo spin valve with TiN spacer

TiN was investigated as a potential spacer material in L1{sub 0}-FePt based pseudo spin valves (PSV). PSVs with the structure MgO/L1{sub 0}-Fe{sub 50}Pt{sub 50} (20 nm)/TiN (5 nm)/L1{sub 0}-Fe{sub 50}Pt{sub 50} (x nm) were fabricated, where x was varied from 5 to 20 nm. The highest giant magnetoresistance (GMR) ratio of 0.61% was obtained for the PSV with a top L1{sub 0}-FePt thickness of 20 nm. Contributions to the GMR arose from both the spin dependent scattering at the FePt/TiN interfaces and domain wall resistivity. Magnon magnetoresistance was also observed in the fabricated PSVs.

36 MATERIALS SCIENCE↗

DOE OSTI2011

Unveiling and Driving Hidden Resonances with High-Fluence, High-Intensity X-Ray Pulses

We show that high fluence, high-intensity x-ray pulses from the world's first hard x-ray free-electron laser produce nonlinear phenomena that differ dramatically from the linear x-ray-matter interaction processes that are encountered at synchrotron x-ray sources. We use intense x-ray pulses of sub-10-fs duration to first reveal and subsequently drive the 1s{r_reversible}2p resonance in singly ionized neon. This photon-driven cycling of an inner-shell electron modifies the Auger decay process, as evidenced by line shape modification. Our work demonstrates the propensity of high-fluence, femtosecond x-ray pulses to alter the target within a single pulse, i.e., to unveil hidden resonances, by cracking open inner shells energetically inaccessible via single-photon absorption, and to consequently trigger damaging electron cascades at unexpectedly low photon energies.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2010

Using strong electromagnetic fields to control x-ray processes.

Exploration of a new ultrafast-ultrasmall frontier in atomic and molecular physics has begun. Not only is is possible to control outer-shell electron dynamics with intense ultrafast optical lasers, but now control of inner-shell processes has become possible by combining intense infrared/optical lasers with tunable sources of X-ray radiation. This marriage of strong-field laser and X-ray physics has led to the discovery of methods to control reversibly resonant X-ray absorption in atoms and molecules on ultrafast timescales. Using a strong optical dressing field, resonant X-ray absorption in atoms can be markedly suppressed, yielding an example of electromagnetically induced transparency for x rays. Resonant X-ray absorption can also be controlled in molecules using strong non-resonant, polarized laser fields to align the framework of a molecule, and therefore its unoccupied molecular orbitals to which resonant absorption occurs. At higher laser intensities, ultrafast field ionization produces an irreversible change in X-ray absorption. Finally, the advent of X-ray free electron lasers enables first exploration of non-linear X-ray processes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗