  We report the fabrication of a directly coupled superconducting quantum
interference device (SQUID) magnetometer in MgB2 using a focused ion beam (FIB)
to create Josephson junctions in a 70 nm thick film of MgB2. The SQUID shows a
voltage modulation (deltaV) of 175 mV at a temperature of 10 K and operates
over a temperature range from 10 K to 24 K. We find excellent agreement between
the measured maximum transfer functions and those predicted by theory. We have
measured the magnetic flux noise at 20 K to be as low as 14 micro Phi-0 per
root Hz.
