We report the fabrication of a directly coupled superconducting quantum interference device (SQUID) magnetometer in MgB 2 using a focused ion beam (FIB) to create Josephson junctions in a 70 nm thick film of MgB 2 . The SQUID shows a voltage modulation (∆V) of 175 µV 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 µΦ 0 Hz -1/2 .

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We have recently developed a technique for fabricating SNS junctions in MgB 2 thin films using a focused ion beam. These junctions show a strong modulation of the critical current by applied magnetic field and microwaves. They also show large I c R N products in excess of 1 mV at 4.2 K making them attractive candidates for a range of superconducting electronics applications. We have made SQUIDs with directly coupled pick-up loops using this technique which show large voltage modulations (175 µV at 10 K) and noise comparable to HTS SQUIDs. Here we will present an overview of our devices along with our latest results.

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