Measurements of magnetic damping in GdFeCo thin films

In this paper, we describe the results of a time-resolved study of the ultrafast magnetic response of Gd_23.1Fe_71.9Co_5.0 MAMMOS structures under the condition near the actual read/write temperature. For the study we used an all-optical pump and probe method in which an intense (pump) light beam excited a medium due to ultrafast laser heating and a less intense (probe) beam monitored this photo-excited state through the magneto-optical Kerr effect. In this way response times and damping can directly be measured in the time domain with femtosecond resolution. Then, the damping factor was determined from the directly fitting of the measured result with model calculation. By an all-optical pump and probe method we demonstrated that the photo-excitation could effectively excite coherent spin waves in the magnetic material. Precession frequencies of several GHz and relaxation times in the nanosecond range were observed.