Ultrafast magnetization dynamics in heterogeneous granular FePt media

摘要: Granular FePt in the L1 0 phase is a key material for future magnetic data storage devices, supporting the smallest stable magnetic domains. Precessional eigenmodes have recently been studied with fs laser pump-probe techniques. Large 400GHz eigenfrequencies are observed due to the huge FePt magnetic anisotropy. However, such optical techniques only measure the collective spin precession of all grains without spatial resolution. Here we investigate the nanoscale aspects of magnetization dynamics in FePt with fs X-ray pulses from the Linac Coherent Light Source at Stanford. We show that optical excitation leads to distinctly different magnetic responses due to the size distribution of FePt grains. While part of the laser-excited magnetic grains follow a small applied magnetic field, others do not. The former display heat assisted magnetic recording. In contrast, the magnetic anisotropy of the latter is not …