Micromagnetic susceptometer for the measurement of the magnetic susceptibility of the actinides

A device with the sensitivity for measuring the magnetic susceptibility of small volume samples (10cm^-3 as a function of temperature from 4.2K to 300k is described as designed specifically for measurements with microgram or submicrogram quantities of the actinide metals. Specifically, results are given for the susceptibility of curium-248 in the temperature range from 4.2K to 300K.

The susceptometer is calibrated with a 7l microgram sphere of lead. From this measurement and the measurements with curium the minimum measurable volume susceptibility for a one microgram, metal sample is determined to be 7.4 x 10 ^-8 (CGS). The temperature of the sample is determined by measuring simultaneously the susceptibility of a sample of Gd₂O₃ in thermal contact with the curium. The magnetic field is measured using the critical field of the lead as a calibrating point. The Gd₂O₃ signal is used as a measure for fields

For a 4l.2 microgram sample of curium-248, measurements were made in fields of .45G and 20.9G. There is evidence for two magnetic transitions. One in the range 77-78K is clearly an antiferromagnetic to paramagnetic transition. The other occurs in the range 187-206K and resembles this type of transition also.