Effect of CoFe composition of the spin-valvelike ferromagnetic tunnel junction

The magnetoresistance (MR) ratio of a ferromagnetic tunnel junction with a spin-valvelike structure of ${\mathrm{NiFe/CoFe}}_x{\mathrm{/Al–O/CoFe}}_x\mathrm{/NiFe/IrMn/Al}$ is dependent upon CoFe composition. MR ratio increases with increasing Fe content, and shows a maximum of 42% for Fe content 26 at. % after annealing at 225 °C. Before annealing, the bias voltage dependence depend on Fe content, however, the bias voltage dependence did not depend on Fe content after annealing. We think that the increasing defect states in the barrier layer with the increasing Fe content in ${\mathrm{CoFe}}_x$ layer cause the degradation of the bias voltage dependence. After annealing, the defect states of samples decrease to same level, and the bias voltage dependencies of samples are improved and become same.