Measurement of magnetic fields at liquid helium temperatures

Two types of magnetometer are described, both capable of measuring magnetic fields to better than 1 G in 25 kG at the temperature of liquid helium. The first is a marginal oscillator of range 7-150 Mc/s employing a single probe throughout this frequency range. 19 F and 23 Na field probes have been satisfactorily used with this oscillator in liquid helium at 25 kG. The extrapolated field capacity of the 23 Na probe used with this oscillator can be as high as 130 kG. The second magnetometer uses a Hall device driven at 400 c/s in conjunction with null-balance a.c. detection. Two types of Hall probe are discussed and typical calibration curves over the region 2-25 kG at 4.2°K are presented.