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 Angstrom)/Fe20Ni80(50 )/IrMn(150 Angstrom)/Co(50 Angstrom)/Al(13 Angstrom)-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 Phi=1.9 eV and the thickness d=12 Angstrom. 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. (C) 2000 American Institute of Physics. [S0021-8979(00)54308-4].