Calibration of ac and dc magnetometers with a Dy2O3 standard.

The ac susceptibility and magnetization curves of a glued Dy(2)O(3) powder sample are measured by an ac susceptometer and a dc superconducting quantum interference device magnetometer, both of which have been calibrated previously. It is shown that the magnetic moment of the paramagnetic sample as a function of field and temperature may be accurately expressed by a combination of the Curie-Weiss law and the Langevin function at T > 45 K with three adjusting parameters, so that the dc magnetization curves and the magnitude and phase of ac susceptibility at different values of dc bias field measured by any magnetometer can be calibrated by using Dy(2)O(3) as a standard. The expressions are empirical and cannot be justified in the entire field and temperature range by existing theories of paramagnetism. Below 10 K, indication of approaching a possible phase transition is found. It is shown that pure Dy(2)O(3) powder may be used as a primary standard, with susceptibility [13.28(T + 17)](-1) emu/Oe/g at T > 50 K and H < 10 kOe, in consistency with the Curie-Weiss law and the quantum mechanical theory of paramagnetism.