D. Collomb, P. Li, and S. J. Bending
Nanoscale graphene Hall sensors for high-resolution ambient magnetic imaging

Magnetic field sensors are used for a very wide variety of purposes, including but not limited to; biosensing, instrumentation and process calibration as well as high precision magnetic field mapping such as Scanning Hall Probe Microscopy (SHPM) and magnetic susceptometry. Although there are many different approaches to magnetic sensing, Hall-effect sensors have frequently been employed due to their high magnetic field sensitivities, quantitative linear response, non-invasive performance and fabrication versatility. This allows them to be used in a range of applications where other semi-quantitative and potentially invasive sensor types, such as magnetic force microscopy (MFM) cantilevers, may not meet requirements. They are also much more compact and simple to use than the recently developed diamond Nitrogen vacancy (NV) centre magnetic microscope, which requires precisely fabricating a single crystal diamond with an NV center at the apex of an AFM tip as well as additional lasers and microwave excitation. The fabrication of Hall probes based on nanoscale wire widths allows high spatial resolution mapping applications to be realised. This requirement is increasingly in demand due to the rapid miniaturisation of modern technologies, for example ultra-high density magnetic storage media or magnetic domain-wall racetrack memory. However, such probes have a much broader range of potential imaging applications including combined high-resolution topographic and magnetic imaging of vortices in superconductors and domains/domain walls in ferromagnetic films based on SHPM with scanning tunnelling microscopy (STM) or atomic force microscopy (AFM) surface tracking. Through the addition of field excitation coils they can also be used to perform highly local magnetic susceptometry.


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