TEMPERATURE-DEPENDENCE OF MAGNETIC ORDER IN UPDSN

The intermetallic compound UPdSn has been studied by means of neutron powder diffraction on a two-axis spectrometer. At the lowest temperature, it is a noncollinear antiferromagnet with magnetic space group P(c)2(1), and a uranium magnetic moment of (2.05 +/- 0.04)mu(B), in agreement with previous work. The structure can be described in terms of the magnitude of the uranium magnetic moment mu and two independent canting angles theta and phi. phi is the angle between the magnetic moment and the c axis; theta is the angle between the in-plane component of the magnetic moment and the b axis. There is no detectable temperature hysteresis in the magnetic order. All three model parameters (mu, theta, and phi) vary continuously with temperature, and there is no evidence from our data of any sharp transitions below the Neel point of 43 +/- 2 K. The angle phi is almost constant over the whole temperature range, while the magnetic moment decreases continuously until it disappears just above 40 K. The angle theta-decreases continuously up to a temperature of about 35 K, where it appears to rise again. In the course of this work, we have also demonstrated the consistency of the results for magnetic systems, whether they are measured by the conventional reactor constant-wavelength technique or by the time-of-flight method on a pulsed spallation source.