Tunnel magnetoresistance effect in tunnel junctions with Co₂MnSi heusler alloy electrode and MgO barrier

We demonstrated that a large TMR ratio of 753 % has been observed at 2 K in a MTJ using a Co₂MnSi Heusler alloy electrode and a crystalline MgO tunnel barrier. At room temperature (RT), we also have observed a large TMR ratio of 217 %, which value at RT is much larger than that of MTJs using an amorphous Al-oxide tunnel barrier. However, the temperature dependence of the TMR ratio was still large. In order to improve the interface, we investigated the TMR effect in Co₂MnSi/CoFeB(0-2 nm)/MgO/CoFe MTJs. TMR ratio was enhanced by inserting a thin CoFeB layer at the Co₂MnSi/MgO interface. The MTJ with CoFeB thickness of 0.5 nm exhibited the highest TMR ratio. From the conductance-voltage measurements for the fabricated MTJs, we inferred that the highly spin polarized electron created in Co₂MnSi can conserve the polarization through the 0.5 nm thick FeB layer.