Nanometer size effect on the structure and magnetic properties of high oxygen content ferromagnetic PrMnO3+δ nanoparticles

Structure and magnetic properties of undoped PrMnO3+δ nanoparticles with average particle size ranging from 40–500 nm have been investigated. Compared with bulk PrMnO3 compound with A type antiferromagnetic ordering below TN=95 K, PrMnO3+δ nanoparticles exhibit ferromagnetic ordering. With decreasing particle size, the MnO6 octahedra distortion increases, the cell volume shrinks, the average Mn–O bond length increases and the Mn–O–Mn bond angle decreases; the ferromagnetism becomes weak and the Curie temperature decreases gradually, and meanwhile, the spin glass behavior becomes more obvious. However, in contrast to antiferromagnetic nanoparticles, no exchange bias phenomenon was observed in our case. These interesting results are attributed to the excessive oxygen content and surface effects.