Metamagnetic transition in a heavy fermion superconductor URu2Si2

We have carried out the magnetization measurements in high magnetic fields up to 60 T and in the wide temperature range from 1.3 to 77 K for a heavy f emion superconductor URu2Si2 A sharp metamagnetic transition with three ste ps is found below 14 K for the field along the tetragonal [001] direction. This transition is changed into a sharp metamagnetic transition with two st eps in a narrow temperature range from about 14 to 17 K and futhermore into a broad metamagnetic transition with one step above the Neel temperature T -N=17.5 K. The broad transition persists up to a characteristic temperature T chi(max) (=55K) where the magnetic susceptibility has a maximum in the t emperature dependence. These results are discussed on the basis of a change of the electronic state of 5f-electrons from itinerant to localized and th e crystalline electric field model.