Optical pump-probe studies of spin dynamics in ferromagnetic materials

In this thesis, time domain investigations of picosecond spin dynamics in ferromagnetic thin films will be presented. These have been performed by means of a magneto-optical pump-probe technique. In this technique, either field pumping or optical pumping is used to excite the spins. In field pumped measurements, optically triggered photoconductive switches have been used to generate transient magnetic field pulses. The response of the sample has been probed by means of a Magneto-Optical Kerr Effect (MOKE) measurement. The experimental set-up and alignment techniques for both field pumping and optical pumping measurements will be discussed in detail. The theory applied in the modelling of the time resolved Kerr rotation data will also be described. The results of field pumped experiments on Fe thin films, Ni81Fe19 thin films of different thickness, and micro-scale Ni81Fe19 elements will be presented. The rise time of the pulsed field within the samples, the damping of the spin precession, and the optimum conditions for magnetisation switching will be presented. A first optical pumping study will be presented in which an ultrafast demagnetising effect is induced in a Nickel foil. (author)