Uniform magnetization precessions are generated by ultrafast optical excitation along the in-plane easy axis [100], as well as along the hard axis [1-10], in epitaxial Fe films grown on AlGaAs (001) over a wide range of applied magnetic fields. From the temporal evolution of the coherent magnetization precession, we determine the magnetic anisotropy constants and damping parameters which are crucial in designing fast magnetic switching devices and spintronics devices. This work is supported in part by the National Science Foundation, the Office of Naval Research, and the DARPA Spins in Semiconductors Program.

Uniform magnetization precession in the ferromagnetic state of La0.67Sr0.33MnO3 films grown on different substrates is investigated in the 50–300K temperature range in magnetic fields of up to 1.3T. The precession was induced by an optical pump pulse and probed by a time-delayed pulse using magneto-optical Kerr effect. The measured field dependence of the precession frequency agrees well with calculation from the Landau-Lifshitz-Gilbert equation using different uniaxial anisotropies for different substrates. The field-dependent relaxation times of the exponentially decaying precession are in 100–1400ps range. This work is supported in part by NSF (DMR-0137322, IMR-0114124, and PSU MRSEC DMR-0213623), DOE (DE-FG02-04ER46127), and the Petroleum Research Fund.

The reversal process of the Fe interface layer magnetization in Fe/AlGaAs heterostructures is measured directly using magnetization-induced second-harmonic generation, and is compared with the reversal of the bulk magnetization as obtained from magneto-optic Kerr effect. The switching characteristics are distinctly different due to interface-derived anisotropy—single step switching occurs at the interface layer, while two-jump switching occurs in the bulk Fe for the magnetic field orientations employed. The angle between the interface and bulk magnetization may be as large as 40–85 degrees. Such interface switching will dominate the behavior of nanoscale structures.

Optically excited uniform magnetization precession in the ferromagnetic state of La0.67Ca0.33MnO3 films grown on different substrates is investigated by the time-resolved magneto-optic Kerr effect. The parameters of magnetic anisotropy are determined from the measured field dependence of the precession frequency. The dominant anisotropy contribution in the film grown on SrTiO3(001) is the strain-induced easy-plane anisotropy. In the strain-free films on NdGaO3(110), we discover a uniaxial in-plane anisotropy that results from the interface due to the tilting of the oxygen octahedra in NdGaO3.

Time-resolved magnetization-induced second-harmonic generation is used to initiate and monitor coherent electronic spin precession in the Fe interface layer of a Fe∕AlGaAs (001) heterostructure. The frequency, phase, and hysteretic behavior of the interface magnetization precession are found to be different from the bulk Fe film. The results indicate that faster magnetization switching can be achieved in nanostructures where interface properties dominate. This work was supported in part by the National Science Foundation, the Office of Naval Research, and the DARPA Spins in Semiconductors Program.