| Time-resolved ferromagnetic resonance (FMR) measurements are performed using a pump-probe technique with a non-optical pump to observe precession and relaxation of the magnetization in epitaxial magnetic thin films at temperatures down to 5 K. Spatial localization achieved through use of an optical probe allows a direct measurement of spin relaxation, reducing the effects of inhomogeneous dephasing relative to probes of larger areas, while the use of low fields allows a study of dynamics throughout the entire magnetization reversal process.; The reversal mechanism of FexCo1-x is probed as a function of cubic and uniaxial anisotropy strengths, using FMR as a direct probe of the free energy surface. A coherent rotation model describes the reversal for fields up through 700 Oe, failing only for fields near 105 Oe applied along the GaAs [01 1¯] direction where nucleation of nearly perpendicular domains is observed. Measurements of the Gilbert damping parameter alpha indicate that it is smaller for fields applied along the [01 1¯] direction than for fields along [011] or [010].; Dynamic interactions between local moments and itinerant carriers are examined in the diluted magnetic semiconductor Ga1-xMn xAs. Holes and local moments are found to precess together on timescales greater than 50 ps. Although previous experiments by other groups have observed a change in the magnetization due to introduction of photoexcited carriers, our measurements indicate no dynamical change in magnetization due to additional optically pumped carriers. The Gilbert damping parameter alpha is observed to increase more than twofold as temperature is raised from 20 K to the Curie temperature, although the decay time remains nearly independent of temperature over this range.; Exchange-biased Fe/FeF2 is found to exhibit temperature-dependent anisotropy above its Neel temperature (78 K), while the anisotropy of structurally similar Fe/MnF2 remains independent of temperature above TN = 67 K. Dynamic hysteresis loops reveal a tendency toward reversal through domain nucleation below 50 K in Fe/MnF2 and above 50 K in Fe/FeF2. |
