POSSIBLE OBSERVATION OF A NEW MAGNETIC PHASE-TRANSITION IN USB

By measuring the polarization of neutrons transmitted through a USb si ngle crystal we have discovered evidence for a second phase transition at T = 142(2) K, about 70 K below TN ( = 213 K), in this well-studie d antiferromagnetic actinide compound. The measurements show that a be am of polarized neutrons abruptly starts to become depolarized at T. A number of other measurements find anomalies at T and we propose tha t the transition is related to dephasing between the components of the triple-k structure known to exist in USb. This dynamic effect causes the formation of fluctuating domain walls containing ferromagnetic com ponents, which then depolarize neutrons.