A SQUID (Superconducting QUantum Interference Device) is the most sensitive device available for measuring magnetic fields, and the SQUID in the MPMS (Magnetic Property Measurement System) is the source of the instrument’s remarkable sensitivity. When the sample moves through a system of superconducting detection coils close to the SQUID, the current from the detection coils inductively couple to the SQUID sensor. When properly configured, the SQUID electronics produce an output voltage proportional to the current flowing in the SQUID input coil. Because all the coils, wires and the SQUID input coil form a closed superconducting loop, any change of magnetic flux in the detection coils produce a change in the persistent current detection circuit, which is proportional to the change in magnetic field. In a fully calibrated system, measurements of the voltage variations from the SQUID detector as a sample is moved through the detection coils provide a highly accurate measurement of the sample’s magnetic moment.
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