Spin polarization in half-metals probed by femtosecond spin excitation

Knowledge of the spin polarization is of fundamental importance for the use of a material in spintronics applications. Here, we used femtosecond optical excitation of half-metals to distinguish between half-metallic and metallic properties. Because the direct energy transfer by Elliot–Yafet scattering is blocked in a half-metal, the demagnetization time is a measure for the degree of half-metallicity. We propose that this characteristic enables us vice versa to establish a novel and fast characterization tool for this highly important material class used in spin-electronic devices. The technique has been applied to a variety of materials where the spin polarization at the Fermi level ranges from 45 to 98%: Ni, Co 2 MnSi, Fe 3 O 4 , La 0.66 Sr 0.33 MnO 3 and CrO 2 . It is now shown that femtosecond optical excitation can be used as a tool to investigate the spin-polarization properties of half-metals, and provide a clear distinction between those and metals. Such knowledge is of fundamental importance for the use of these materials in spintronics applications.