Tunnel magnetoresistance effect in magnetic tunnel junctions using a Co₂MnSi(110) electrode

Magnetic tunnel junctions (MTJs) with half-metallic electrodes are expected to show a large tunnel magnetoresistance (TMR) ratio, according to Julliere's model. A Co₂MnSi Heusler alloy is theoretically expected to possess a half-metallic electronic state. Experimentally, at low temperature, Co ₂MnSi(100)/Al-oxide/CoFe junctions exhibited a large TMR ratio. We fabricated MTJs with high-quality (110)-oriented Co₂MnSi electrodes and investigated the TMR effects. We obtained a TMR ratio of about 40% at room temperature and 120% at 2 K, respectively. However, we observed degradation of the energy gap of Co₂MnSi in the minority spin band from the conductance-voltage characteristics. We infer that the interface of Co ₂MnSi(110) possesses no half-metallic property.