Anomalous pressure effect on the magnetic ordering in multiferroic BiMnO3

Abstract

We report the magnetic field dependent dc magnetization and the pressure-dependent (pmax ∼ 16 kbar) ac susceptibilities χp(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.