Transmission electron microscopy of Co₂(Cr_1-xFe_x)Al sputtered films and their magnetic tunneling junctions

The microstructures of Co₂FeAl and Co₂(Cr_0.4Fe_0.6)Al sputtered films and of their magnetic tunnel junctions (MTJs) have been investigated to discuss the possible reasons for an unexpectedly low tunneling magnetoresistance (TMR). The structure of the Co₂FeAl film changed from B2 to L2₁ with increasing substrate temperature, while that of the Co₂(Cr_0.4Fe_0.6)Al film remained B2 up to 500 °C. The thermodynamically predicted phase separation was not observed in the films. The low TMR values obtained from the MTJs using the Co₂FeAl and Co₂(Cr_0.4Fe_0.6)Al films are attributed to the low-spin polarization expected from the low degree of order in these films. The TMR values depend sensitively on the interfacial structure of the tunnel junctions when the degree of order of the film is low.