Some Techniques for Sensitive Magnetic Measurements Using Superconducting Circuits and Magnetic Shields

Abstract

A new superconducting circuit has been used in a sensitive magnetic susceptibility apparatus to detect changes in magnetic susceptibility as small as 10−10 cgs/g in a 104 Oe field, and in a low field magnetometer with which magnetic fields as low as 5×10−7 Oe have been measured. A low field superconducting shield for testing sensitive magnetometers has been developed and used to provide stable magnetic fields of less than 10−6 Oe, maintained stably for as long as six days. The measured attenuation of externally applied axial field changes is shown to be a factor of about 31 per shield radius. The stability of the persistent field of a Nb-25% Zr superconducting solenoid, observed over an 8 h period, indicated an average drift in the persistent solenoid field of less than one part in 1010/sec. Also, the attenuation of various high field magnetic shields of Nb-25% Zr foil was measured.