A scanning superconducting quantum interference device microscope for room temperature samples

We have constructed a scanning low-Tc superconducting quantum interference device (SQUID) microscope, in which the SQUID is mounted on the lower end of a copper rod and cooled to liquid helium temperature. There is a 65µm thick sapphire window under the SQUID. The sample at room temperature underneath the window can be scanned to produce magnetic images. The microscope has a spatial resolution of 100-150µm and a magnetic field sensitivity of 3-60pT/√ Hz in a magnetically unshielded environment. We have used this scanning SQUID microscope to measure various room temperature samples.