Detection of individual iron-oxide nanoparticles with vertical and lateral sensitivity using domain wall nucleation in CoFeB/Pt nanodevices

We present new studies of the characteristics and detection ability of nanoscale sensors based on domain wall nucleation within perpendicularly magnetised ultrathin CoFeB/Pt films. A combination of MFM imaging and anomalous Hall effect transport measurements were used to verify and characterise the behaviour of fabricated devices. After initial characterisation, the influence of magnetic nanoparticles on device behaviour was studied using individual iron oxide (FeOx) particles mounted on modified atomic force microscopy probes. We demonstrate the successful detection of particles ranging in diameter between 2.8 μm and 100 nm. In the case of the 2.8 μm particle, we have mapped the signal amplitude produced at a variety of distances from the sensor. We find that the particle’s influence may be detected at separations up to 700 nm. Furthermore, we demonstrate a method for resolving the location of a particle with respect to the centre of the device, providing a lateral sensing ability.