Abstract
X-ray magnetic circular dichroism (XMCD) measurements have been performed under high pressure and used to study the disordered Fe72Pt28 Invar alloy. The well-known high spin to low spin state transition is observed at 4 GPa. In addition, XMCD evidences a second transition to the nonmagnetic phase at high pressure in the disordered alloy. This result is made unambiguous by comparison to the ordered alloy whose hysteresis cycle of the phase transitions is dramatically different from the disordered alloy. The pressure-dependent collapse of the Curie temperature is the dominant mechanism for reducing the magnetization only in the ordered alloy.