Synthesis, structure and magnetic properties of nanocrystalline YMnO3

Nanocrystalline YMnO3 has been prepared by wet chemical synthesis routes to obtain crystallites with sizes from 20 nm to bulk material. The crystal structure of hexagonal YMnO3 nanocrystallites smaller than 80 nm deviates from bulk material in terms of unit cell distortion and unit cell volume. The ferrielectric displacements of Y3+ cations along the polar c-axis decays progressively with decreasing size below 100 nm. Indications of weak ferromagnetism in the form of a narrow hysteresis loop and enhanced magnetic susceptibility below 43 K in 20 nm YMnO3 nanoparticles is attributed to extrinsic effects. Low-temperature annealing of the 20 nm crystallites in an oxidizing atmosphere removed all traces of ferromagnetism, showing that this is not a size-induced property. Finally, formation of the competing metastable orthorhombic phase and the thermodynamically stable hexagonal phase is discussed with respect to oxidizing or reducing conditions during synthesis.