Unexpected phase locking of magnetic fluctuations in the multi-k magnet USb

The spin waves in the multi-k antiferromagnet, USb, soften and become quasielastic well below the AFM ordering temperature, T_N. This occurs without a magnetic or structural transition. It has been suggested that this change is in fact due to de-phasing of the different multi-k components: a switch from 3-k to 1-k behaviour. In this work, we use inelastic neutron scattering with tri-directional polarisation analysis to probe the quasielastic magnetic excitations and reveal that the 3-k structure does not de-phase. More surprisingly, the paramagnetic correlations also maintain the same clear phase correlations well above T_N (up to at least 1.4T_N). This precursor regime has not been observed before in a multi-k system.