Micro-Hall effect probes for applications at pulsed magnetic fields above 75 T

Microminiature Hall probes (MHP) may be used as magnetic field transducers, with virtually no change of sensitivity with temperature, for applications at room and cryogenic temperatures. The probes have a nominal active sensing area of 90x90 µm and are based on Sn-doped n-InSb/i-GaAs MBE-grown heterostructures. Previously MHPs were intensively tested [1] and shown to be appropriate for various applications in the temperature range 50 mK- 300 K and in pulsed magnetic fields up to 52 T (of 120 ms pulse duration). The latest probes, with overall dimensions of 150x750 µm, are the smallest encapsulated Hall probes currently available and can be placed in areas not previously accessible to commercial packaged sensors. The new MHP modification has recently been tested in pulsed magnetic fields above 75 T using a new 9 MJ dual-coil magnet designed and fabricated at the Dresden High Magnetic Field Laboratory. The inner coil, having a bore of 20 mm, produced a 10 ms pulse on top of the 30 T background field from the outer coil of 100 ms duration. Tests over the range 300 K to 78 K yielded a remarkably linear Hall voltage up to 76.7 T, with a temperature independent sensitivity of 2.3 µV/mT (at an input current of 5 mA). The Hall-device input resistance was less than 0.4 ohms and < 1.5 ohms including the 80 mm long MHP copper wires.