Automated induction magnetometer

Abstract

An automated, high sensitivity, digital magnetometer operating on the induction principle and utilizing a 50-kOe superconducting coil has been constructed. The sample is moved between two 16 000-turn coils and the time integral of the induced voltage pulse (proportional to the magnetic moment) is integrated by an electronic voltage-to-frequency converter and counting system. At the same time, the magnetic field and the temperature are obtained as the output from digital voltmeters. The resolution of the instrument is 10 -4 emu, and is independent of the applied field, temperature, and sample moment. Evaluation of the magnetometer was made with measurements on a 0.218-g EuO single-crystal sphere oriented with H along a [111] easy axis of magnetization. From several sets of data at 4.2°K the fluctuations of the moment-field curve had a mean deviation of one part in 8000. At 1.4°K and 15 kOe the specimen is about 99.8% saturated and from 15 to 50 kOe the moment is given by the relation, σH=σ0[1-a/H]+bH, where H is the applied field, σ0=225.0±1.0 emu/g, a≈24 Oe, and b≈1.0×10-6cm3/g. The 1/H term represents a 0.1% volume of the sample which is difficult to saturate probably because of imperfections and strains in the sample. © 1967 The American Institute of Physics.