New features in the vortex phase diagram of YBa2Cu3O7- delta

Magnetic and transport measurements have been performed in high quality YBa2Cu3O7- delta single crystals. We demonstrate for the first time that the magnetization peak line in the phase diagram of YBa2Cu3O7- delta , Hp(T) exhibits an impressive similarity with the equivalent line for Bi2Sr2CaCu2O8. Our results show not only a similar temperature dependence but also an almost identical response to oxygen doping and a correlation to the multicritical point. At high temperatures we observe a previously unreported splitting of the magnetization peak.