The straining effect on tunneling resistance of Co∕AlOx∕Co∕IrMn junctions

The authors have fabricated a series of Co∕AlOx(d0)∕Co∕IrMn magnetic tunnel junctions (MTJs), with d0=12–30A. They can be used as ultrasensitive strain gauges. From the resistance (R) versus strain (Δe) curve, the authors find that the maximum value of the gauge factor (γmax) is as large as 5000–20000 in the low-strain (∣Δe∣⩽25×10−6) range. Furthermore, the response is linear. Two mechanisms are proposed to explain the piezoresistance behavior of these MTJs: one is due to the tunneling magnetoresistance effect (the magnetic origin) and the other due to the ordinary tunneling effect (the nonmagnetic origin).