SQUID (Superconducting Quantum Interference Device) magnetometer
The S700X SQUID magnetometer is the most sensitive instrument for DC and AC measurements of the magnetic properties of material samples as a function of magnetic field and temperature. The SQUID sensor at the core of the system has a noise power sensitivity of about 10-30 joules/root(Hz). This sensitivity is two orders of magnitude better than any semiconductor system and enables the measurement of extremely small magnetic signals with great accuracy and high speed.
The S700X has several operating options. The most common is the measurement of total magnetic moment, which is done by moving the sample through a set of pick-up coils. During the measurement, the sample temperature and the applied magnetic field are precisely controlled. The second-order gradiometer configuration used for the pick-up coils is insensitive to the externally applied field, but allows easy resolution of samples with 10-11 Am2 total moment.
The superconducting magnets used are wound from wires using a copper-stabilised superconductor. This coil is then vacuum impregnated with epoxy resin to form a composite structure with excellent mechanical strength and electrical insulation. The pick-up coil set is formed as part of the magnetic structure.
A built-in µ-metal magnetic shield reduces the ground field and provides a sample environment of typically 10 milligauss. The combination of these two features with the low current option allows accurate measurements in the range of 10 milligauss to 150 gauss.
The system also has a complete magnetic shield built into the cryostat to protect the measurement system from external influences and ensure a background field of typically 100 µT at the sample measurement point.