  We report the magnetic field dependent dc magnetization and the
pressure-dependent (pmax ~ 16 kbar) ac susceptibilities Xp(T) on both powder
and bulk multiferroic BiMnO3 samples, synthesized in different batches under
high pressure. A clear ferromagnetic (FM) transition is observed at TC ~ 100 K,
and increases with magnetic field. The magnetic hysteresis behavior is similar
to that of a soft ferromagnet. Ac susceptibility data indicate that both the FM
peak and its temperature (TC) decrease simultaneously with increasing pressure.
Interestingly, above a certain pressure (9 ~ 11 kbar), another peak appears at
Tp ~ 93 K, which also decreases with increasing pressure, with both these peaks
persisting over some intermediate pressure range (9 ~ 13 kbar). The FM peak
disappears with further application of pressure; however, the second peak
survives until present pressure limit (pmax ~ 16 kbar). These features are
considered to originate from the complex interplay of the magnetic and orbital
structure of BiMnO3 being affected by pressure.
