Evidence of Fermi level control in a half-metallic Heusler compound Co ₂ MnSi by Al-doping: Comparison of measurements with first-principles calculations

The Fermi level (E_F) control of half-metallic Heusler alloy Co₂ MnSi by Al-doping was challenged in magnetic tunnel junctions with a Co₂ MnAl_x Si_1-x (CMAS) electrode. The observed bias voltage dependence on tunneling conductance (G-V curves) clearly shows a shift in E_F toward the center of the half-metallic gap with x, which showed excellent agreement with our first-principles calculations. However, the ratio of tunnel magnetoresistance (TMR) at 10 K to that at room temperature does not exhibit a remarkable change with x. The weak exchange energy at the CMAS interface may be the origin for the large temperature dependence of the TMR ratio.