The famous cart-wheel design multiloop dc SQUID magnetometers, designed and fabricated by PTB-Berlin are available in three different sensitivities.
The most sensitive L type magnetometer is realized on a 7 x 7 mm² chip with a field sensitivity of 0.46 nT/Phi0 and a typical field noise level as low as 1.3 fT/sqrt(Hz) at 100 Hz. This device is ideal for biomagnetic applications as well as sensitive characterization of magnetically shielded rooms and geophysical applications.
The M type magnetometer with a field sensitivity of 3 nT/Phi0 is based on a 3 x 3 mm² substrate with a noise level of 3.6 fT/sqrt(Hz). It is designed for minimum coupling between sensors in multichannel systems. The robust device can be cooled in the Earth magnetic field without degragation of noise. It is ideal if you do not need the ultra-low noise level of the L type with reduced shielding requirements.
The S type magnetometer is fabricated on a 3 x 3 mm² chip too with a pickup-loop diameter of 1.7mm. The field sensitivity of 7 nT/Phi0 and the noise level of about 8.4 fT/sqrt(Hz) makes it the ideal sensor for magnetically unshielded operation, e.g. as a monitoring device outside of a superconducting shield.