Spin polarization of Co2MnGe and Co2MnSi thin films with A2 and L21 structures

Spin polarizations (P) of polycrystalline Co2MnGe and Co2MnSi films that were sputter deposited on thermally oxidized Si substrates at various substrate temperatures (T-s) were measured by the point contact Andreev reflection technique. While continuous films were grown at T-s = 500 degrees C with the L2(1) structure, Mn-deficit islands were formed at T-s > 700 degrees C. P showed strong dependence on the state of order of the alloys; P = 0.58 for L2(1) ordered Co2MnGe, P = 0.35 for A2 Co2MnGe, P = 0.54 for L2(1) ordered Co2MnSi, and P = 0.52 for A2 Co2MnSi. The experimentally determined P values of the L2(1) ordered films are lower than the theoretical predictions, which is attributed to the imperfect L2(1) ordering. (c) 2007 American Institute of Physics.