Miniature SQUID susceptometer

We present a new dc superconducting quantum interference device (SQUID) configured as a susceptometer for the study of the magnetic properties of small (<10 μm) particles and thin-film samples. The SQUID consists of two series pick-up loops wound in opposite sense over a hole in the groundplane and connected to remotely located tunnel junctions by low inductance transmission lines. An integrated field coil with provision for balance allows application of a magnetic field of 0-30 G to a sample positioned in either pick-up loop. For an applied field of 5 G the device having an intrinsic energy sensitivity of ∼25 h is able to resolve the superconducting transition of a 5-μm tin particle with a signal-to-noise ratio of ∼106.