An Attempt to measure spin-polarization of Heusler alloy CoMnSi using spin-polarized positron annihilation

Kawasuso, Atsuo; Sakuraba, Yuya*; Fukaya, Yuki   ; Zhang, H.; Maekawa, Masaki; Mochizuki, Izumi; Takanashi, Koki*

We are attempting to determine the spin-polarization of the Heusler alloys using spin-polarized positron annihilation spectroscopy. Positrons implanted near the surface combine with electrons to form positronium (Ps). From the o-Ps (spin triplet state) fraction, one can determine the electron spin-polarization. The samples used in this study are CoMnSi films grown on MgO(001) substrates. To avoid the surface oxidation, the sample surfaces are capped with Au thin layers (0.5 nm thick). The electron polarization are obtained to be 0.26. This is significantly smaller than that determined by using the Andreev reflection method. The further study using samples without any cap layers are needed.