Not all SQUIDs are squids…!

Low Temperature Physical Measurement Platform (MPBT)

To be found in the newsletter of the UFR of Chemistry “Sorbonne University” of March 30, 2023

Every unpaired electron in a material or molecule generates a small magnetic moment. The interactions of these magnetic moments with each other determine the magnetization of the system. To measure it, we often use the SQUID magnetometer. “SQUID” here does not mean “squid”, but “Superconducting Quantum Interference Device”. During a magnetic measurement, the sample passes vertically through a gradiometer consisting of superconducting loops. The vertical movement of the sample in the gradiometer produces a very weak electric current whose intensity depends on the magnetization of the sample. This gradiometer is coupled to a superconducting loop with one or two Josephson junctions (non-supra zone). The Josephson loop is hyper-sensitive to magnetic flux variations and thus allows to measure magnetizations with extreme sensitivity. To put it in physics terms: the SQUID is a quantum interferometer based on the Josephson effect. The SQUID magnetometer allows measurements in the temperature range 1.8-400 K and under magnetic field 0 – 7 T. It allows to obtain information on the electronic structure of materials and it is an indispensable tool for all researchers whose activity concerns the study of magnetic nanoparticles, geo-materials, superconductors and thin film semiconductors, molecular magnetic materials, etc… 

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Yanling LI