Measurement of the magneto-optical response of Fe and CrO${}_2$ epitaxial films by pump-probe spectroscopy: Evidence for spin-charge separation

We have investigated the magneto-optical response of Fe and CrO${}_2$ epitaxial films by pump-probe polarimetry, showing that charge and spin dynamics can be unambiguously disentangled. The time-resolved Kerr ellipticity and rotation in the metallic sample are essentially identical after the initial transient (shorter than a picosecond), but they considerably differ in the oxide film, even tens of picoseconds past the optical excitation. These differences are determined by the combined effects of photoexcited charge carriers and spins on the Kerr signal, but a detailed polarimetric analysis can explicitly unravel these contributions. In addition, the diagonal and off-diagonal terms of the dielectric tensor can be retrieved, providing the complete dynamical characterization of magnetic and optical properties in a ferromagnet, which is of utmost importance to understand spin evolution in magnetically correlated complex oxide materials.