We have investigated the crystal structure and magnetic moment of the Co2 FeAl and Co2 FeSi films deposited onto thermally oxidized Si and MgO(100) single-crystal substrates, and the structural effect on the tunnel magnetoresistance (TMR) of the magnetic tunnel junctions (MTJs) using a Co2 FeZ (Z=Al or Si). The structure was changed by the substrate and postannealing temperatures, in which the fully epitaxial and polycrystalline Co2 FeAl and Co2 FeSi films were obtained with the different disorder structure. The magnetic moment of Co2 FeAl films was found to be uninfluenced by the crystal structure. Spin-valve-type MTJs consisting of Co2 FeZ (100 nm) Al (1.2 nm) -oxide Co75 Fe25 (2 nm) IrMn (10 nm) Ta (60 nm) were fabricated (Z=Al or Si) on thermally oxidized Si and MgO(100) single-crystal substrates. The maximum TMR obtained is about 50% at room temperature for MTJs with Co2 FeAl films, regardless of the crystal structure of Co2 FeAl.
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