Vibration measurements of a scanning SQUID microscope in a cryogen-free dilution refrigerator

Scanning probe microscopy is more challenging in cryogen-free systems due to vibrations introduced at the sample by the cryocooler. We built a cryogen-free scanning superconducting quantum interference device (SQUID) magnetic probe microscope operating in a cryogen-free dilution refrigerator with a base temperature of 10 mK. We report characterization of both the vibrations at the mixing chamber plate and of probe-to-sample vibrations. For the latter, we follow Schliessl et al. (Appl. Phys. Lett. 109, 232601 (2016)) and measure noise spectra at multiple locations above a sample where strong magnetic field gradients are present. This allows us to disentangle vibrations in different spatial directions. We find that the most pronounced vibrations are below 10 nm/Hz^1/2 and occur at low harmonics of the pulse tube cycle. We will also discuss future improvements to our microscope and refrigerator that will further reduce the vibrations in our system.