Antiferromagnetism and superconductivity in URu2Si2

We have performed neutron scattering measurements of the temperature dependence of the antiferromagnetic Bragg peak intensity for the heavy fermion system URu2Si2, as it enters the superconducting phase. Temperature scans were carried out in zero magnetic field and field scans through the upper critical field were also made with the field along the c-axis. The behaviour of the ordered moment upon entering the superconducting phase limits the possible types of pairing. Our results exclude isotropic singlet state pairing but d wave pairing is possible.