Advanced SQUID-on-lever scanning probe for high-sensitivity magnetic microscopy with sub-100-nm spatial resolution

Superconducting quantum interference devices (SQUIDs) are exceptionally sensitive magnetometers, capable of detecting weak magnetic fields. Miniaturizing these devices and integrating them onto scanning probes enables high-resolution imaging at low temperatures. Here, we fabricate nanometer-scale niobium SQUIDs with inner-loop sizes down to 10nm at the apex of individual planar silicon cantilevers via a combination of wafer-scale optical lithography and focused ion beam (FIB) milling. These robust SQUID-on-lever probes overcome many of the limitations of existing devices, achieving spatial resolution better than 100 nm, magnetic flux sensitivity of 0.3 μφ0/Hz, and operation in magnetic fields up to about 0.5 T at 4.2 K. Nanopatterning via Ne- or He-FIB milling allows for the incorporation of a modulation line for coupling magnetic flux into the SQUID or a third Josephson junction, for shifting its phase. Such advanced functionality, combined with high spatial resolution, large magnetic field range, and the ease of use of a cantilever-based scanning probe, extends the applicability of scanning SQUID microscopy to a wide range of magnetic, normally conducting, superconducting, and quantum Hall systems. We demonstrate magnetic imaging of skyrmions at the surface of bulk Cu2OSeO3. Analysis of the point spread function determined from imaging a single skyrmion yields a full width at half maximum of 71 nm. Moreover, we image modulated magnetization patterns with a period of 65 nm.