Local current distribution in a ferromagnetic tunnel junction measured using conducting atomic force microscopy

The local electrical properties were measured simultaneously with the topography for a Ta(50 Å)/Fe20Ni80(50 Å)/IrMn(150 Å)/Co(50 Å)/Al(13 Å)-oxide junction. The electrical image showed the contrast with around a few nm lateral size and a strong correlation with the topographical image was not observed. In the local current–voltage characteristics, data within the bias voltage of ±1.5 V were fitted well to Simmon’s equation and we obtained the barrier height Φ=1.9 eV and the thickness d=12 Å. On the other hand, data with the bias voltages higher than 3 V were fitted well to Fowler–Nordheim equation. The histogram of current density was calculated by taking into consideration a Gaussian distribution of the barrier thickness and the height. The distribution of the barrier height can explain the experimental result realistically.