for use in anti-submarine warfare as a magnetic anomaly detector (MAD) fitted to maritime patrol aircraft. SQUIDs are used in superparamagnetic relaxometry (SPMR), a technology that utilizes the high magnetic field sensitivity of SQUID sensors and the superparamagnetic properties of magnetite nanoparticles. These nanoparticles are paramagnetic; they have no magnetic moment until exposed to an external field where they become ferromagnetic. After removal of the magnetizing field, the nanoparticles decay from a ferromagnetic state to a paramagnetic state, with a time constant that depends upon the particle size and whether they are bound to an external surface. Measurement of the decaying magnetic field by SQUID sensors is used to detect and localize the nanoparticles. Applications for SPMR may include cancer detection. See also Aharonov–Bohm effect Electromagnetism Geophysics Macroscopic quantum phenomena Notes References American inventions Measuring instruments Superconductivity Josephson effect Magnetometers