Magnetic tunnel junction field sensors with hard-axis bias field.

We have fabricated and studied the magnetic properties of the Ni[SUB81]Fe[SUB19]/Al[SUB2]O[SUB3]/Ni[SUB81]Fe[SUB19] based magnetic tunnel junction sensors. Magnetoresistance (MR) of 35% is achieved with a small applied field (< 10 Oe). The introduction of a hard axis bias field linearizes the MR response. The hysteresis disappears in hard-axis fields greater than 3 Oe, which corresponds to the effective anisotropy field along the easy axis. A sensitivity of 3.5%/Oe has been demonstrated in this linear region. Low-frequency noise measurements indicate that sensor noise is dominated by field-dependent 1/ƒ noise caused by magnetization fluctuations. Finally, a noise level as low as 1 nT/Hz[SUP1/2] has been obtained. [ABSTRACT FROM AUTHOR]