Spin-torque sensor with tunable sensitivity and detection range

A linear magnetic-field sensor utilizing a MgO-based spin-transfer torque magnetic tunnel junction (STT-MTJ) is demonstrated in this study. In order to obtain a linear field sensor, the behaviour of the resistance, R, versus the magnetic field, H, is controlled by the application of bipolar voltage pulses. The R(H) loops are collapsed completely and show a linear response to the applied field with a sensitivity of 4.21%/Oe in the sensing mode. This loop-collapsing method, i.e. eliminating coercivity, is an important technique in the design of STT-MTJ sensors. The bipolar pulse-driven STT-MTJ sensor was observed to have adjustable sensitivity. Furthermore, the linear response region could be intentionally shifted by applying a varying direct current voltage. This bipolar pulse-driving method for realizing a tunable field sensor is a good candidate for embedded multifunctional sensing devices.