Magnetostriction and tunneling magnetoresistance of CoFeB∕AlOx∕Co∕IrMn junctions

Abstract

Cross-strip magnetic tunnel junctions (MTJs) were fabricated following this sequence: Si(100)∕Ta(30Å)∕CoFeB(80Å)∕AlOx(to)∕Co(70Å)∕IrMn(90Å)∕Ta(100Å), under an in-plane deposition field (h)=500Oe, where to=12, 17, 22, and 26Å is the thickness of the AlOx layer. From the resistance (Ro) versus to plot, Ro increases from 255to1138Ω exponentially, as to increases from 12to26Å. This indicates that the quantum tunneling mechanism is valid in our case. Furthermore, the tunneling magnetoresistance (TMR) increases initially from 49% to 63% and then decreases to 33%, as to increases monotonically. This shows that with the increase of the barrier thickness, to⩾17Å, the spin polarization in the current after tunneling is weakened eventually. The microstructure of the to=17Å MTJ observed under high-resolution cross-sectional transmission electron microscope shows that the interfaces between CoFeB∕AlOx and AlOx∕Co are smooth, resulting in the high TMR ratio observed. Saturation magnetostriction (λs) of this series of CoFeB∕AlOx∕Co MTJs ranges from −5to−2ppm. The λs versus to plot also shows the concave-up feature. Finally, we find that the optimal MTJ has the following properties: TMR=63% and λs=−5ppm.