Photoinduced Demagnetization and Insulator-to-Metal Transition in Ferromagnetic Insulating BaFeO_{3} Thin Films.

We studied the electronic and magnetic dynamics of ferromagnetic insulating BaFeO_{3} thin films by using pump-probe time-resolved resonant x-ray reflectivity at the Fe 2p edge. By changing the excitation density, we found two distinctly different types of demagnetization with a clear threshold behavior. We assigned the demagnetization change from slow (∼150 ps) to fast (<70 ps) to a transition into a metallic state induced by laser excitation. These results provide a novel approach for locally tuning magnetic dynamics. In analogy to heat-assisted magnetic recording, metallization can locally tune the susceptibility for magnetic manipulation, allowing one to spatially encode magnetic information.

Ultrafast spin-switching of a ferrimagnetic alloy at room temperature traced by resonant magneto-optical Kerr effect using a seeded free electron laser.

Ultrafast magnetization reversal of a ferrimagnetic metallic alloy GdFeCo was investigated by time-resolved resonant magneto-optical Kerr effect measurements using a seeded free electron laser. The GdFeCo alloy was pumped by a linearly polarized optical laser pulse, and the following temporal evolution of the magnetization of Fe in GdFeCo was element-selectively traced by a probe free electron laser pulse with a photon energy tuned to the Fe M-edge. The results have been measured using rotating analyzer ellipsometry method and confirmed magnetization switching caused by ultrafast heating.

Observation of a Devil's Staircase in the Novel Spin-Valve System SrCo6O11.

Using resonant soft-x-ray scattering as a function of both temperature and magnetic field, we reveal a large number of almost degenerate magnetic orders in SrCo6O11. The Ising-like spins in this frustrated material in fact exhibit a so-called magnetic devil's staircase. It is demonstrated how a magnetic field induces transitions between different microscopic spin configurations, which is responsible for the magnetoresistance of SrCo6O11. This material therefore constitutes a unique combination of a magnetic devil's staircase and spin-valve effects, yielding a novel type of magnetoresistance system.

Direct measurement of oscillatory generation of superoxide anions by single phagocytes.

Phagocytic cells such as neutrophils generate superoxide anions (O2-) within phagocytic vacuoles for killing and digesting microorganisms. Here we report the simultaneous observation of morphological changes and O2- generation in single phagocytic cells during phagocytosis. Point stimulation of a cell by contact with an opsonized microelectrode at the cell surface induced significant deformation to engulf the electrode, and also induced the O2- generation which was measured by the electrode. Periodic fluctuations in the magnitude of the O2- generation were observed in the time course. These oscillations may be caused by metabolic regulation of the formation of NADPH, which is the substrate for the O2- generation