Background signals in SQUID magnetometers

Since a SQUID magnetometer is an extremely sensitive device capable of detecting minute magnetic flux changes in a sample, it will also detect unwanted signals from materials near the magnetometer. The presence of temperature dependent "background signals" limits the accuracy of measurements of the temperature variation of the magnetization of a sample. Measurements of the magnetization from IK down to 0.OIK of materials used in the construction of the magnetometer described here show that these materials are responsible for the background signals. From these data, magnetometers can be designed so that the background contribution introduces an uncertainty of less than one flux quantum for a temperature change from IK down to 0.01K in a field of 100 Oe.