Magnetostriction and Tunneling Magnetoresistance of Co/AlOx/Co/IrMn Junctions

Cross-strip magnetic tunnel junctions (MTJs) were fabricated following this sequence: Si(100)/Ta(30 angstrom)/Co(75 angstrom)/AlOx (delta t(o))/Co (75 angstrom)/IrMn(90 angstrom)/Ta(100 angstrom) was deposited under an in-plane deposition field (h) = 500 Oe, where fit. = 12, 17, 22, and 26, and 30 A was the thickness of the AlOx layer. Tunneling magnetoresistance (TMR) rose initially from 21% to 36% and then fell to 24 % delta t(o) increased monotonically. This means the spin tunneling weakened as delta t(o) >= 26 angstrom. The magnetostriction (lambda(s)) of the Co/AlOx/Co MTJs was generally in the range of -23 ppm to -12 ppm. Moreover, the lambda(s) vs. delta t(o) plot shows the concave-up feature. High-resolution sectional transmission electron microscope (HR X-TEM) with nanoprobe energy dispersive x-ray (EDX) spectroscopy was used to analyze the Co, Al, and O concentrations across each AlOx. layer. The different concentration dependences along delta t(o) resulted in the lambda(s) feature. In addition, HR X-TEM, showed that in the microstructure of each Co/AlOx/Co MTJ, the interfaces of Co/AlOx and AlOx/Co are smooth. We find that the optimal MTJ in this series has the following properties: TMR = 36% and lambda(s) = -15 ppm.