The Superconducting Magnetic Flux Detector

A superconducting magnetic flux detector which can detect changes in flux as small as 10−11 G·cm2 is now in use in a small number of low temperature laboratories. We describe here how the devices work, how they are made, how they can be used for practical measurements of magnetic susceptibilities or fields, and how they can be made even more sensitive. The devices can easily be used in work other than low temperature physics and should find widespread application.