Femtosecond photomagnetic switching of spins in ferrimagnetic garnet films.

We demonstrate that intense laser pulses can be used to directly control the spins in ferrimagnetic garnet films. Through an ultrafast and nonthermal photomagnetic effect the magnetocrystalline anisotropy is modified to create a new long-lived equilibrium orientation for the magnetization. Simultaneously, the magnetization is rotated into this new state by precession in a strong transient optically generated magnetic field. All take place within the 100 fs duration of a single laser pulse, thus demonstrating the feasibility of photomagnetic switching on the femtosecond time scale.

In situ studies of phase transitions in thin discotic films.

The crystalline to liquid crystalline (Cr-LC) phase transition in thin films of zone-cast hexa-peri-hexabenzocoronene sixfold substituted with dodecyl side chains (HBC-C12H25) has been studied in detail using grazing incidence X-ray diffraction (GID), electron diffraction (ED), and variable angle spectroscopic ellipsometry (VASE), When heating the material, a first minor transition is observed around 42 degrees C. This change is attributed to alterations of the crystalline alkyl chain packing, which only slightly changes the electronic properties of the material. At higher temperatures of about 90 degrees C, but still significantly below the previously reported transition temperature in bulk, the Cr-LC transition is observed. An accompanying large increase in optical anisotropy is compatible with the X-ray data, showing a transition from the as-cast herringbone-like crystalline state to a highly ordered discotic hexagonal columnar LC phase. The structural transition has the macroscopic effect of increasing the film thickness. The high structural order of the as-cast low-temperature phase is only partly recovered after cooling, and the phase transition exhibits a large hysteresis. From the ellipsometry data, the dielectric tensor of HBC-C12H25 was refined to unprecedented detail.