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. (c) 2006 American Institute of Physics.