Magnetic circular dichroism in the extreme ultraviolet (XUV) spectral range is a powerful technique for element-specific probing of magnetization in multicomponent magnetic alloys and multilayers. We combine a high-harmonic generation source with a λ/4 phase shifter to obtain circularly polarized XUV femtosecond pulses for ultrafast magnetization studies. We report on simultaneously measured resonant magnetic circular dichroism (MCD) of Co and Ni at their respective M 2,3 edges and of Pt at its O edge, originating from interface magnetism. We present a time-resolved MCD absorption measurement of a thin magnetic Pt/Co/Pt film, showing simultaneous demagnetization of Co and Pt on a femtosecond time scale.

Femtosecond excitation of SrRuO 3 nanolayers in a SrRuO 3 / SrTiO 3 superlattice quenches their ferromagnetism, resulting in magnetostriction. The buildup of mechanical stress is observed in real time by mapping lattice motions via ultrafast x-ray diffraction. A rise time of 500 fs is found for a wide range of excitation wavelengths. In the ferromagnetic phase, phonon-mediated ͑ ph ͒ and magnetostrictive stress ͑ M ͒ components display similar strengths but opposite signs. The amplitude of M follows the temperature dependent magnetization M 2 ͑T͒ whereas the strength of ph is determined by the amount of deposited energy.

Strain propagation in a perovskite heterostructure grown on a SrTiO 3 ͑STO͒ substrate is studied by ultrafast x-ray diffraction. Femtosecond displacive phonon excitation in a PbZr 0.2 Ti 0.8 O 3 / SrRuO 3 ͑PZT/SRO͒ film launches acoustic strain waves propagating into the STO substrate. We demonstrate a two-step time evolution of diffracted x-ray intensity which originates from different interfering contributions to the ͑004͒ Bragg peak of the STO substrate. Analysis by dynamical x-ray diffraction theory gives the absolute strain ⌬a / a 0 in a wide range of optical pump fluences. Ultrafast transient strain as small as ⌬a / a 0 =2ϫ 10 −5 is determined in this way.

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Coherent zone-folded longitudinal acoustic phonons (ZFLAPs) were measured nondestructively with subpicometer spatial and sub-picosecond time resolution via ultrafast X-ray diffraction (XRD). The femtosecond excitation of a GaAs/AlGaAs superlattice with 1.5 eV photons results in spatially periodic stress, which induces a coherent ZFLAP with a 3.5 ps period. The motion is directly monitored by femtosecond X-ray pulses at a kilohertz repetition rate. The intensity change 0 03 R R D / = . of the -1 st order satellite peak of the (002) . The phase and amplitude of the oscillatory XRD signal around a new equilibrium demonstrates the displacive excitation of coherent phonons (DECP) as the dominant mechanism for strong excitation. We discuss different mechanisms which account for impulsive stress, and argue that the electronic stress due to the deformation potential dominates.