Time-resolved study of the increased magnetization precession frequency in Fe wires

We have performed time-resolved pump-probe measurements on arrays of 1μm-wide Fe wires and on a 50μm-wide Fe stripe. A photoconductive switch was used as a source of fast-risetime magnetic field pulses. The magnetization dynamics were detected by the magneto-optical Kerr effect. We find that the ferromagnetic resonance frequency of the wires is about 16 GHz and twice as large as that of the wide Fe stripe. This corresponds to an oscillation period of the magnetization precession of about 60 ps at small bias field. We attribute this fast precession to the shape anisotropy of the Fe wires.