  As charge carriers traverse a single superconductor ferromagnet interface
they experience an additional spin-dependent phase angle which results in spin
mixing and the formation of a bound state called the Andreev Bound State. This
state is an essential component in the generation of long range spin triplet
proximity induced superconductivity and yet the factors controlling the degree
of spin mixing and the formation of the bound state remain elusive. Here we
demonstrate that point contact Andreev reflection can be used to detect the
bound state and extract the resulting spin mixing angle. By examining spectra
taken from La1.15Sr1.85Mn2O7 single crystal - Pb junctions, together with a
compilation of literature data on highly spin polarised systems, we show that
the existence of the Andreev Bound State both resolves a number of long
standing controversies in the Andreev literature as well as defining a route to
quantify the strength of spin mixing at superconductor-ferromagnet interfaces.
Intriguingly we find that for these high transparency junctions, the spin
mixing angle appears to take a relatively narrow range of values across all the
samples studied. The ferromagnets we have chosen to study share a common
property in terms of their spin arrangement, and our observations may point to
the importance of this property in determining the spin mixing angle under
these circumstances.
