Ultrafast Optical Parametric Pumping Of Magnetization Reorientation And Precessional Dynamics In Dyfe2/Yfe2 Exchange Springs

The magnetization dynamics of a wound [DyFe2(20 angstrom)/YFe2(80 angstrom)](x40) exchange spring multilayer have been explored in optical pump probe experiments. Ultrafast optical heating was used to modify the magnetic parameters of the multilayer, while the time resolved magneto-optical Kerr effect was used to probe its response. Although the probe signal is dominated by precession and winding of the exchange spring within the soft YFe2 layer, reorientation of the DyFe2 hard-layer magnetization is detected on time scales less than 100 ps. Micromagnetic simulations reproduce the main features of the experimental data and indicate a dramatic optically induced reduction of the hard-layer anisotropy. The results establish the feasibility of switching a spring system by means of parametric excitation.