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 scatt ering, specific heat, electrical resistivity, and magnetic susceptibil ity measurements. Two single crystals prepared under identical conditi ons received different heat treatments. One crystal was annealed, the other was used as-grown. While the macroscopic properties and the magn etic excitations are essentially the same for the two crystals, the ma gnetic Bragg peak intensity have completely different temperature depe ndences. Despite this, the low-temperature magnetic moment is iidentic al for the two samples, showing that the small moment of 0.023(3) mu(B ) is intrinsic. The finite correlation length (similar to 500 Angstrom ) appears to be related to defects. We discuss the relevance of itiner ant versus localized behavior of the 5f electrons responsible for the magnetism, and the possibility of two successive phase transitions.