強磁性トンネル接合の局所伝導特性と磁気抵抗効果

抄録

The local electrical properties were measured simultaneously with the topography for a Ta(50Å)/Fe₂₀Ni₈₀(50Å)/IrMn(150Å)/Co(50Å)/Al(d_AlÅ)-oxide junction. The electrical image showed the contrast with a lateral size of around a few nm, and no strong correlation with the topography was observed. By analyzing the local current-voltage characteristics, we found that the contrast of the current image showed the distribution of the barrier height. This may be due to the lack of the oxygen from the stoichiometry of the Al₂O₃ composition. We measured the current images for junctions with shorter oxidation times and with lower Al thicknesses. The histogram of current densities was calculated by taking into consideration the Gaussian distribution of the barrier height. It fitted the experimental results well except for the junction with thin Al; this may be due to a local leakage current. The tunneling magnetoresistance (TMR) ratio was considered to be reduced by this current.