Magnetic property in the ferromagnetic superconductor UGe2 at pressures above the ferromagnetic critical pressure

We have studied the high-pressure magnetic property in UGe2 where ferromagnetic superconductivity appears under high pressure. In this study, we focus on the magnetic property at pressures above the ferromagnetic critical pressure Pc =1.6 GPa. The temperature and magnetic field dependences of the dc-magnetization have been measured under high pressures up to 5.1 GPa by using a ceramic anvil high pressure cell. At pressures above Pc, the magnetic susceptibility x shows a broad maximum around Tχmax and the magnetization at 2.0 K shows an abrupt increase (metamagnetic transition) at Hc. With increasing pressure, the peak structure in x becomes broader, and the peak position Tχmax moves to the higher temperature region. The metamagnetic field Hc increases rapidly with increasing pressure. At pressures above 4.1 GPa, x shows a simple temperature dependence, and the magnetization increases linearly with increasing field. These phenomena in UGe2 resemble to those in the intermetallic compounds of 3d transition metals such as Co(S1−xSex) and YCo2. We discuss the experimental results by using the phenomenological spin-fluctuation theory.