Scanning SQUID microscopy in a cryogen-free dilution refrigerator

Scanning probe microscopy in cryogen-free refrigerators is challenging due to vibrations introduced by the cryocooler. We have implemented a magnetic flux microscope using a scanning superconducting quantum interference device (SQUID) in a cryogen-free dilution refrigerator with a base temperature of 10 millikelvin. We report on our design of the microscope and present progress toward a detailed analysis of the vibrations in the system. These include vibrations of the cold plates in the refrigerator measured with geophones and sample-to-probe vibrations obtained from analyzing noise spectra near a localized source of magnetic field. Following Schiessl et al. (Appl. Phys. Lett. 109, 232601 (2016).), we can determine the x, y, and z components of the sensor-sample vibrations. Finally, we discuss strategies to further reduce vibrations in our refrigerator.