Magnetostriction and Tunneling Magnetoresistance of Co/AlO$_{{\rm x}}$/Co/IrMn Junctions

Abstract

Cross-strip magnetic tunnel junctions (MTJs) were fabricated following this sequence: Si(100)/Ta(30 Å)/Co(75 Å)/AlO x ( t o )/Co (75 Å)/ IrMn(90 Å)/Ta(100 Å) was deposited under an in-plane deposition field (h) = 500 Oe, where t o = 12 17 22, and 26, and 30 Å was the thickness of the AlO x layer. Tunneling magnetoresistance (TMR) rose initially from 21% to 36% and then fell to 24% as t o increased monotonically. This means the spin tunneling weakened as t o 26 Å. The magnetostriction ( s ) of the Co/AlO x /Co MTJs was generally in the range of 23 ppm to 12 ppm. Moreover, the s vs. 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 AlO x layer. The different concentration dependences along t o resulted in the s feature.In addition, HR X-TEM, showed that in the microstructure of each Co/AlO x /Co MTJ, the interfaces of Co/AlO x and AlO x /Co are smooth. We find that the optimal MTJ in this series has the following properties: TMR = 36% and s = 15 ppm.