Low-frequency noise of high T-c superconducting quantum interference device (SQUID) magnetometer fabricated on bicrystal substrate

The excess low-frequency noise of a high T-c superconducting quantum interf erence device (SQUID) magnetometer fabricated on bicrystal substrate is stu died. Direct-coupled magnetometers are fabricated using different geometric s of the pickup coil, and the relationship between the geometry of the pick up coil and the low-frequency noise of the magnetometer is studied. It is s hown that the weak superconducting region in the pickup coil, which is auto matically formed on top of the grain boundary of the bicrystal substrate, i s one of the main sources of the excess noise. By selecting an appropriate geometry of the pickup coil, we can significantly decrease the excess noise of the magnetometer without decreasing its effective area.