Magnetic Particle Nanosensing by Nucleation of Domain Walls in Ultra-Thin CoFeB/Pt Devices

A novel nanosensor is demonstrated based on domain-wall (DW) nucleation in perpendicular-anisotropy CoFeB/Pt components, with an electrical read-out based on the anomalous Hall effect. Notch-shaped constrictions within perpendicular CoFeB/Pt wires are used to control the local anisotropy. The successful detection of a single NdFeB microbead is demonstrated, based on the variations in DW nucleation in a notched nanowire in the presence of the bead. Maps of the sensor response obtained using scanning gate microscopy measurements are presented. We describe a number of potential advantages of the nucleation-sensing technique as compared with existing DW-based magnetic bead sensors using in-plane magnetized materials.