Fabrication of Magnetic Tunnel Junctions With Co-2 FeSi Heusler Alloy and MgO Crystalline Barrier

Abstract

Tunneling magnetoresistance (TMR) characteristics of magnetic tunnel junctions with a Co-2 FeSi electrode and an MgO crystalline barrier have been investigated. Co-2 FeSi Hensler alloy electrode grown on Cr-buffered MgO(100) substrate starts to have an L2(1) structure when annealed above 420 degrees C. In the cases of CoFeB/MgO/Co-2 FeSi junctions, a high TMR ratio of 158% has been achieved after annealing at 350 degrees C, which is obtained by coherent tunneling between the electrodes and barrier, not by the half-metallic nature of Co-2 FeSi Heusler alloy. However, the Co-2 FeSi Hensler alloy electrode degrades the TMR ratio when compared with an amorphous CoFeB electrode and the bottom Co-2 FeSi electrode makes more degradation of the TMR ratio than the top Co2FeSi electrode. The major reason for the low TMR ratio in Co-2 FeSi-based junctions is the broken epitaxial relationship between the bottom Co-2 FeSi electrodes and the MgO crystalline barrier, which is investigated by a cross-sectional transmission electron micrograph.