  Many Heusler compounds are predicted to be ferromagnetic half metals in the
bulk, which makes them promising compounds for spintronics. However, for
devices the transport spin polarization at specific interfaces requires
optimization. We show that investigations of the unidirectional
magnetoresistance provide an alternative approach to access this quantity.
Based on a Wheatstone-bridge design we probed the unidirectional
magnetoresistance of Co2MnSi/(Ag, Cu, or Cr)(0.5 nm)/Pt (or Ta) multilayers and
separate the spin-dependent unidirectional spin Hall magnetoresistance from
other contributions. We demonstrated that by the insertion of a thin epitaxial
Ag layer the spin-dependent contribution is doubled corresponding to a
significant increase of the transport spin polarization, which is discussed in
the framework of highly spin polarized interface states.
