Local transport properties of ferromagnetic tunnel junctions

The local electrical properties were measured simultaneously with the topography for a SiO2/Ta(3nm)/ I Fe20Ni80(3 nm)/Pt(20nm)/Fe20Ni80(3 nm)/IrMn(10 nm)/Co75Fe25(4 nm)/Al(0.8 nm)-oxide junction. The current image became very homogeneous and smooth after annealing at around 300 C for 1 h. Increase of tunneling magnetoresistance ratio of the junction after annealing can be well explained by taking into account both increase of the barrier height and decrease of the barrier height variation. After further annealing over 350 C. the barrier height decreased and leak currents were detected. Reduction of spin polarization of the ferromagnetic electrodes due to interface mixing or damage of the insulator due to the growth of grains of bottom electrode is a possible reason for the drastic decrease of TMR ratio for annealing at temperatures higher than 350 C. (C) 2001 Elsevier Science B.V. All rights reserved.