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The annealing effects on magentoresistance (MR) values for the top and bottom spin valves are examined. The MR value of bottom spin valves declines with the increase in annealing temperature and disappears at the blocking temperature of 200 degrees C whereas the MR value of the top valves rises to the maximum at the annealing temperature of 100 degrees C and then decline with the further increase in the annealing temperature to about 250 degrees C.

The tunneling magnetoresistance (TMR) ratio, resistance, barrier height, barrier thickness and bias dependence along the wedge are examined. The bias dependence of magnetoresistance (MR) ratio is found to be symmetric in underoxidized regions and asymmetric in overoxidized regions.

Transmission electron microscopy, high-resolution electron microscopy, and electron holography are used to study the microstructure of CoFe/AlO(sub x)/Co magnetic tunnel junctions (MTJs) isochronally annealed up to 400 degree centigrade. It was found that at 400 degree centigrade more Co and Fe atoms diffused into the oxide barrier layer caused the sip-flip scattering of the spin polarized electrons at the barrier layer, leading to the decrease of the TMR value.