Magnetometry at liquid helium temperatures

Abstract The main aim of the article is to survey the present situation in the rapidly expanding field of Superconducting Quantum Interference Device (SQUID) magnetometry. Initially, however, the sensitivity and experimental limitations of conventional (i.e. non-superconducting) instruments me established in a brief survey of some popular low-temperature megnetometers. Subsequently, the origin of the periodic response of both the single and double weak link SQUIDS is explained by simple considerations of the properties of superconducting circuits. The magnitude of the period, 2 × 10−15 Wb, allows the construction of e flux detector of extreme sensitivity. The various geometries of SQUID devices and the ways in which these are incorporated into convenient magnetometer systems are discussed. Some details are given of the attainable noise levels. The many possible uses of SQUIDS are detailed and examples are given of some of the striking measurements which have already been achieved.