Neutron scattering studies on URu2Si2

This paper aims to review some of the neutron scattering studies performed on URu2Si2 in Grenoble. This compound has been studied for a quarter of century because of a so-called hidden-order ground state visible by most of the bulk experiments but almost invisible by microscopic probes like neutrons, muons NMR or X-ray. We stress on some aspects that were not addressed previously. Firstly, the comparison of the cell parameters in the 1-2-2 systems seems to point that the magnetic properties of URu2Si2 are leading by an U4+ electronic state. Secondly, a compilation of the different studies of the tiny antiferromagnetic moment indicates that the tiny antiferromagnetic moment has a constant value which may indicate that it is not necessarily extrinsic. We also present the last development on the magnetic form factor measurement in which the magnetic density rotates when entering in the hidden-order state. To end, the thermal dependence of the two most intense magnetic excitations at Q(0) = (1,0,0) and Q(1) = (0.6,0,0) seems to indicate two different origins or processes for these excitations.