Biomedical subjects

S B Choe

Publications and source records attributed to S B Choe.

3 recordsLinked to original sources

PubMed2004

Vortex core-driven magnetization dynamics.

Time-resolved x-ray imaging shows that the magnetization dynamics of a micron-sized pattern containing a ferromagnetic vortex is determined by its handedness, or chirality. The out-of-plane magnetization in the nanometer-scale vortex core induces a three-dimensional handedness in the planar magnetic structure, leading to a precessional motion of the core parallel to a subnanosecond field pulse. The core velocity was an order of magnitude higher than expected from the static susceptibility. These results demonstrate that handedness, already well known to be important in biological systems, plays an important role in the dynamics of microscopic magnets.

Journal Article↗

PubMed2002

Quantum interference of virtual and real amplitudes in a semiconductor exciton system.

By two-color pulse shaping, we simultaneously create virtual and real amplitudes for excitons in GaAs quantum wells, and monitor population and amplitude by pump-probe and four-wave mixing spectroscopies. Excited-state probability amplitude can be induced by the off-resonant, virtual excitations as well as by the resonant, real excitations. Population modulation in time-domain results from the interference between the virtual and real amplitudes, and the modulation depth reveals the relative contributions of these two amplitudes. The fact that virtual and real amplitudes have a phase difference of 90 degrees is demonstrated directly in time-domain.

Journal Article↗

PubMed2001

Observation of unequal activation volumes of wall-motion and nucleation processes in Co/Pd multilayers.

We report the difference in activation volumes of wall-motion and nucleation processes in Co/Pd multilayers. Each activation volume was estimated from field dependence of wall-motion speed and nucleation rate, obtained by real-time domain imaging using a magneto-optical Kerr effect microscope. Delicate analysis shows that the two activation volumes are generally unequal and the ratio between the volumes varies noticeably from 0.9 to 1.1 with change of the multilayered structure. We found that the inequality in the two activation volumes has a crucial influence on magnetization reversal behavior: a process having a smaller activation volume dominates.

Journal Article↗