Gap formation and magnetic ordering in URu2Si2 probed by high-field magnetoresistance

We examine the phase diagram of the antiferromagnetic heavy-fermion superconductor URu2Si2 with resistivity experiments in continuous magnetic fields up to 25 T The phase transition that occurs in zero field at T-N=T-0=17.5 K is accompanied by the formation of a tiny staggered magnetic moment of mu=0.04 mu(B). The resistivity anomaly at T-0 reflects the formation of an energy gap Delta. The resulting phase diagram clearly distinguishes the T-0(H) phase boundary and earlier observed high-field (mu(0)H similar or equal to 40 T) field-induced phase transitions towards a large magnetic moment state. Surprisingly, the magnetic field dependence of mu, determined by previous neutron-scattering experiments, strongly differs from that of T-0 and Delta, with estimated critical fields of 14.5 T for mu and similar or equal to 40 T for T-0 and Delta. This observation suggests that there are two energy scales relevant to the magnetic phase transition of URu2Si2.