Influence of sample quality on the magnetic properties of URu₂Si₂

The influence of the sample quality on the magnetic properties of the heavy-fermion superconductor URu2Si2 has been studied by neutron scattering, specific heat, electrical resistivity, and magnetic susceptibility measurements. Two single crystals prepared under identical conditions received different heat treatments. One crystal was annealed, the other was used as-grown. While the macroscopic properties and the magnetic excitations are essentially the same for the two crystals, the magnetic Bragg peak intensity have completely different temperature dependences. Despite this, the low-temperature magnetic moment is identical for the two samples, showing that the small moment of 0.023(3) μB is intrinsic. The finite correlation length (∼ 500 Å) appears to be related to defects. We discuss the relevance of itinerant versus localized behavior of the 5f electrons responsible for the magnetism, and the possibility of two successive phase transitions