Magnetic microscope based on YBCO bicrystal thin film do SQUID operating at 77 K

We have developed two versions of magnetic flux microscope which use an YBCO thin film bicrystal do SQUID to image the two-dimensional distribution of magnetic field. With the size of the inner hole of the SQUID close to 30 μm a spatial resolution of about 200 μm and a field of view 3×4 mm 2 have been obtained. The equivalent magnetic field noise in the SQUID ranges from 100 pT/Hz −1/2 at 1 Hz to 10 pT/ Hz −1/2 at 100 Hz. We have employed the microscope to image 50 μA 110 Hz ac currents flowing in the thin parallel wires.