Coupled antiferromagnetic-ferroelectric transition, higher compensation temperature and enhanced exchange bias in SmFeO3 nanoparticles

In transition metal oxides, quantum confinement arising from a large surface to volume ratio often gives rise to novel physico-chemical properties at nanoscale. Their size dependent properties have potential applications in diverse areas, including therapeutics, imaging, electronic devices, communication systems, sensors and catalysis. We have analyzed structural, magnetic, dielectric, and thermal properties of weakly ferromagnetic SmFeO3 nanoparticles of sizes about 55 nm and 500 nm. The nano size particles exhibit four distinct features that are neither observed in their larger size variants nor reported previously for the single crystals. For 55 nm particle, we observe six fold enhancement of compensation temperature, unusual rise in susceptibility in the temperature range 550 to 630 K due to spin pinning, strong exchange-bias effect at low temperatures and coupled antiferromagnetic-ferroelectric transition, directly observed in the dielectric constant of nano size particle is anomalously sharper.