Vibrational spectroscopy using sum-frequency generation has been used to
investigate the coupling between a ferromagnetic thin film and adsorbed
molecules, here CO on Ni/Cu(100). The CO stretching vibration exhibits a
strong magnetic contrast with a pronounced temperature dependence, underlining
the high sensitivity of this adsorbate-specific spectroscopy method. Our
results indicate that the strong temperature dependence is caused by dynamical
changes in the surface chemical bond when the CO stretch vibration is coupled
to thermally excited external vibrational modes
