Nanoscale Magnetic Tunnel Junction Sensing Devices With Soft Pinned Sensing Layer and Low Aspect Ratio.

Highly sensitive nanosensors with high spatial resolution provide the necessary features for high-accuracy imaging of isolated magnetic nanoparticles or mapping of magnetic fields. Here, we fabricated nanosensor devices based on MgO-magnetic tunnel junctions with soft pinned sensing layer. The exchange interaction at the free-layer is tuned to yield distinct linear operation ranges for the nanosensors. Circular (diameter D = 120–500 nm) and elliptical pillars with low aspect ratio (120 nm \times 130 nm–120 nm \times 200 nm) displaying a linear non-hysteretic transfer curves with tunnel magnetoresistance values up to 143% were obtained. A noticeable improvement in the sensitivity for circular structures from an average value of \sim 1 %/mT up to \sim 2 Hz with Hooge parameters within 1– 3 \times 10^{-9} \mu m ^{2}$ in the linear range. Nevertheless, such high sensitivity values are a major improvement in comparison with those reported previously for nanometric sensors, and extremely competitive with values reported for micrometric spin-valve sensors, with the advantage of providing a reduced device footprint suitable for highly resolved measurements. [ABSTRACT FROM AUTHOR]