Tunnel Magnetoresistance in Full-Heusler Co2FeAl0.5Si0.5-Based Magnetic Tunnel Junctions

Abstract

We fabricated fully epitaxial magnetic tunnel junctions (MTJs) with full-Heusler Co2FeAl0.5Si0.5 (CFAS) electrodes using the sputtering method. We changed the MgO barrier thickness, the thickness of an Mg layer inserted between the CFAS and MgO layers, and a post-annealing process for CFAS layers in order to obtain conditions necessary for achieving a high tunnel magnetoresistance (TMR) ratio. We found that both the MgO barrier thickness and the post-annealing temperature directly influenced the TMR ratio while the thin Mg layer insertion did not. Post-annealing at higher temperatures above 873 K suppresses the TMR ratio due to degradation of the structure of top CFAS layer during the post-annealing. In addition, a large effective tunnel barrier height was observed in our MTJs because of the poor quality of MgO barrier layer. These facts indicate that the tunneling spin polarization of CFAS/MgO interface is sensitive not only to the degree of ordering of L21 or B2 in CFAS but also to the quality of the MgO barrier and CFAS/MgO interfaces.