The magnetization dynamics of single-crystalline Fe͑001͒ thin films with Cr cap layers has been studied by an all-optical time-resolved pump-probe technique. The system is characterized by a fourfold in-plane magnetic anisotropy. We observed long-lived ͑ϳ1 ns͒ magnetization oscillations caused by the ultrafast ͑ϳ0.15 ps͒ optical pulse excitation. The oscillations are associated with the temporal variation of the magnetization component M z normal to the film surface. The phase of the

more »

... s is independent of the polarization state of the pump beam giving evidence for a predominantly thermal origin of the excitation. The amplitude of the oscillations considerably depends on the in-plane orientation and magnitude of the magnetic field. The azimuthal variation of the oscillation frequency at constant magnetic field follows the fourfold in-plane magnetic anisotropy. Angle and field variations of the frequency are well described by a uniform precession mode known from the theory of ferromagnetic resonance. Our analysis indicates that the precession amplitude is determined by the frequency of the uniform mode and an in-plane tilting of the effective magnetic field directly caused by the pumping light beam.