  Decrease of spin polarization in spintronics devices under an application of
bias voltage is one of currently important problems which should be solved. We
reveal unprecedented robustness of spin polarization in multi-layer graphene
spin valves at room temperature. Surprisingly, the spin polarization of
injected spins is constant up to a bias voltage of +2.7 V and -0.6 V in
positive and negative bias voltage applications, which is dramatically superior
to all spintronics devices. Our finding is induced by suppression of spin
scattering due to an ideal interface formation. Furthermore, we firstly report
on important accordance between theory and experiment in molecular spintronics
by observing the fact that signal intensity in a local scheme is double of that
in a non-local scheme as theory predicts, which provides construction of a
steadfast physical basis in this field.

Materials Science;Other Condensed Matter