Anomalous temperature dependence of the mu(+) Knight shift and the phase diagram of UPd3

摘要

We report on first transverse field (0.6 T) measurements on a single crystal of dhcp-UPd3 as a function of orientation and temperature (2-300 K). The TF-mu SR signal showed a splitting into two components with an amplitude ratio 2:1. Rotating the applied field B-ext in the basal plane of the crystal no anisotropy in the precession frequencies was observed. implying axially symmetric mu(+)-positions. The three known phase transitions in UPd3 (two reflecting quadrupolar order below similar to 7.8 K and similar to 6.5 K and antiferromagnetic order below similar to 4.5 K) were visible more or less pronounced in the Knight shift and/or the relaxation rates. Generally, the majority component was more strongly affected. The temperature dependencies of the Knight shifts are complex, showing sign changes and changes in slope. We interpret this to reflect the different magnetic responses of the U-ions at the quasi-cubic and the hexagonal sites (a-site, c-site). Below T-N similar or equal to 4.5 K we do not observe any substantial additional line broadening in contrast to expectations. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 7]