  We present a novel approach to study the spin and symmetry electronic
properties of buried interfaces using low-energy spin-resolved photoemission
spectroscopy. We show that this method is sensitive to interfaces buried below
more than 20ML (~4nm) MgO, providing a powerful tool for the non-destructive
characterization of spintronics interfaces. As a demonstration, we apply this
technique to characterize the Co2MnSi/MgO interface, a fundamental building
block of state-of-the-art magnetic tunnel junctions based on Heusler compounds.
We find that a surface state with {\Delta}1 symmetry and minority spin
character dominating the electronic structure of the bare Co2MnSi(100) surface
is quenched at the Co2MnSi(100)/MgO interface. As a result, the interface
spin-dependent electronic structure resembles the theoretically expected
Co2MnSi bulk band structure, with majority spin electronic states of both
{\Delta}1 and {\Delta}5 symmetry. Furthermore we find an additional
thermally-induced contribution in the minority channel, mirroring the
{\Delta}1/{\Delta}5 asymmetry of the majority channel.
