Temperature dependent resistance of magnetic tunnel junctions as a qualityproof of the barrier

Tunnel junctions of Co(10 nm)/AlOx (nominally 2 nm)/Co(20 nm) have been pre pared by molecular beam epitaxy applying a shadow mask technique in conjunc tion with an UV light-assisted oxidation process of the AlOx barrier. The q uality of the AlOx barrier has been proven by x-ray photoelectron spectrosc opy and temperature dependent tunneling magnetoresistance (TMR) measurement s. Optimum-oxidized tunnel junctions show a TMR of 20% at 285 K and up to 3 6% at 100 K. At 285 K the TMR values as a function of oxidation time are no t symmetric about the optimum time. For underoxidized junctions the TMR is reduced more strongly than for overoxidized junctions. The temperature depe ndence of the junction's resistance is a clear and reliable indicator wheth er pinholes (or imperfections) contribute to the conduction across the barr ier. (C) 2001 American Institute of Physics.