Temperature dependence and annealing effects on spin dependent tunnel junctions

The temperature and annealing effects on junctions with high (10-13 M Omega mu m(2) ) and low (25-30 k Omega mu m(2) ) resistance-area products were s tudied. Junction tunneling magnetoresistance (TMR) is almost unchanged and above 20% up to 200 degrees C. A sharp and reversible TMR decrease is obser ved between 200 and 220 degrees C and is due to the exchange loss in the pi nning layer. Junction TMR increases from 22% to 26% in high resistance-area product samples (resistance decreases a factor of 2), and from 22% to 37% (resistance increases 30% ) in low resistance-area product samples, upon an neal up to 200-230 degrees C. Rutherford backscattering (RBS) analysis of t he oxygen distribution in as-deposited samples indicates oxygen asymmetry i n the barrier. This asymmetry and asymmetry in barrier parameters, found in as-deposited samples, disappear after anneal at 200 degrees C. Two regimes for the TMR dependence on anneal are proposed. The first up to 200 degrees C, where TMR increases, as barrier is homogenized and polarization near th e top electrode increases. The second, above 200 degrees C in low-resistanc e junctions, where TMR increase is related with barrier height increase. (C ) 1999 American Institute of Physics. [S0021-8979(99)35708-X].