Possibilities and limitations of point-contact spectroscopy for measurements of spin polarization

Major issues that limit the applicability of point-contact Andreev reflection (PCAR) spectroscopy for measurements of transport spin polarization (P) are investigated. We show that the analysis of the PCAR spectra on the basis of the generalized Blonder-Tinkham-Klapwijk model may lead to degenerate solutions; i.e., the straightforward determination of P from the multiparameter fitting is ambiguous. We have developed a refined method of analysis that reduces the ambiguity. This method is applied to several test cases (copper, NiMnSb, Co2MnSi, Sr2FeMoO6), and it is found to work in materials with low and high P.