Excitation of coherent spin waves at ultrafast thermomagnetic writing

We present results of a time-resolved study of the ultrafast magnetic response of [Gd.sub.23.1] [Fe.sub.71.9] [Co.sub.5.0] magnetically amplified magnetooptical systems (MAMMOS) structures under conditions near actual read/write temperatures. An all-optical pump and probe method was used 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 magnetooptical Kerr effect. Our experiment clearly demonstrates that the photo-excitation effectively excites coherent spin waves in the magnetic material. Precession frequencies of several gigahertz and relaxation times in the nanosecond range were observed. Index Terms--Magnetization precession, MAMMOS, thermomagnetic writing.