Effect of particle size on magnetic properties of LaMnO3+δ nanoparticles

Magnetic properties of nanocrystalline LaMnO3+δ manganites with particle sizes of 20 (LMO20), 25 (LMO25), and 30 nm (LMO30), prepared by the citrate method, have been investigated. All nanoparticles exhibit paramagnetic to ferromagnetic transition (PFT) at TC>200K. It was found that the relative volume of the ferromagnetic phase increases with increasing particle size and approaches a value of about 93% for LMO30. Ac susceptibility of LMO20 sample exhibits strong frequency dependence below TCTC, whereas for LMO30 sample only weak frequency dependence was observed. The magnetization of LMO30 sample exhibits a PFT of second order. It was found that an applied pressure enhances TCTC of LaMnO3+δ particles with a pressure coefficient of dTC/dP≈1.4–1.9K/kbar for all samples. Peculiar magnetic memory and negative magnetization effects observed for LMO20 sample are discussed.