Direct observation of half-metallic energy gap in Co2MnSi by tunneling conductance spectroscopy.

Magnetic tunnel junctions with a Co2MnSi/Al–O/CoFe structure are prepared by magnetron sputtering and investigated with respect to the energy gap near the Fermi energy level. The plasma oxidation time for the Al–O barrier is found to affect the condition of the Co2MnSi/Al–O interface. The optimized sample (50 s oxidation time) exhibits a magnetoresistance ratio of 159% and tunneling spin polarization of 0.89 at 2 K. The bias voltage dependence of tunneling conductance (dI/dV-V) reveals a clear half-metallic energy gap at 350–400 meV for Co2MnSi, with an energy separation of just 10 meV between the Fermi energy and the bottom edge of conduction band. [ABSTRACT FROM AUTHOR]