SQUID Magnetometer:

• Superconducting quantum Interference Device (SQUID) magnetometers are classified within the flux methods of measuring magnetization of a sample. This is useful to measure small magnetic fields in a most sensitive way.

• Principle: The measurement of the flux change through a pick-up coil system with a SQUID, which is based on the flux quantization within a superconducting loop. This signal is proportional to the magnetic moment of a sample which is magnetized by the magnetic field produced by a superconducting magnet.

Figure 30.05: Schematic of SQUID.

The phase difference of two current paths around a loop in Figure 30.05 is based on the flux through the loop:

To avoid scattering of these two paths, the difference must be multiples of 2π., thus limiting the flux allowed within the superconducting loop to multiples of Φ₀.