Spin polarization of Co2 MnGe and Co2 MnSi thin films with A2 and L 21 structures

Spin polarizations (P) of polycrystalline Co2 MnGe and Co2 MnSi films that were sputter deposited on thermally oxidized Si substrates at various substrate temperatures (Ts) were measured by the point contact Andreev reflection technique. While continuous films were grown at Ts =500 °C with the L 21 structure, Mn-deficit islands were formed at Ts >700 °C. P showed strong dependence on the state of order of the alloys; P=0.58 for L 21 ordered Co2 MnGe, P=0.35 for A2 Co2 MnGe, P=0.54 for L 21 ordered Co2 MnSi, and P=0.52 for A2 Co2 MnSi. The experimentally determined P values of the L 21 ordered films are lower than the theoretical predictions, which is attributed to the imperfect L 21 ordering.