MAGNETIC MICROSCOPY USING A LIQUID-NITROGEN COOLED YBA2CU3O7 SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE

We have developed a magnetic flux microscope which uses a liquid nitro gen cooled thin-film YBa2Cu3O7 dc superconducting quantum interference device (SQUID) to produce two-dimensional images of magnetic fields. The instrument operates as a scanning probe microscope with a spatial resolution of about 80 mum and a field of view of about 100 mm2. The e quivalent magnetic field noise in the SQUID ranges from 80 pT Hz-1/2 a t 1 Hz to 20 pT Hz-1/2 at 1 kHz, yielding a field resolution of about 200 pT in our images. We have used the microscope to image magnetic do mains in ferromagnetic samples, small currents flowing in fine wires, and trapped flux and diamagnetic susceptibility in superconducting thi n films.