Ultrafast magnetism: The magneto-optical Kerr effect and conduction electrons

Most experiments on ultrafast magnetodynamics have been conducted using the magneto-optical Kerr effect. Here, we compare the Kerr effect's magnetic sensitivity to the spin dynamics measured by photoemission. The magnetization dynamics on an Fe/W(110) thin film are probed by spin-resolved photoemission spectroscopy and the Kerr effect. The results reveal similarities between the spin dynamics at low binding energy and the response probed by the Kerr effect. Therefore, the Kerr effect probes states relevant for spin transport and spin flips but may not be sensitive to the entire magnetic moment in femtosecond spin dynamics experiments.