Ferromagnetism in LaMnO3 Nanoparticles Prepared by Sol–Gel Method Combined with Polyvinyl Alcohol

Abstract

This work presents the synthesis of rhombohedral LaMnO3 nanoparticles (NPs) by using a sol–gel method with the assistance of polyvinyl alcohol (PVA), followed with annealing at 700°C for 2 h in air. By changing the PVA amount from 0 ml to 15 ml, we have synthesized LaMnO3 NPs so that their ferromagnetic–paramagnetic phase-transition temperature (T C) can be tuned in the range between 228 K and 305 K. At 15 K, saturation magnetization (M s) and coercivity (H c) values are tunable in the ranges of 32–52 emu/g and 200–258 Oe, respectively, if varying PVA amount from 0 ml to 15 ml. X-ray photoelectron analyses revealed a large amount of La deficiency and oxygen excess in the NPs, particularly for the NPs synthesized with the presence of PVA at a suitable amount (≤10 ml). This leads to a coexistence of Mn3+ and Mn4+ ions, and changes the geometrical structure of nanocrystalline LaMnO3 NPs, as confirmed by x-ray absorption data. We believe that the variation of PVA changed the concentration ratio of Mn3+/Mn4+, enriching a magnetic-phase diagram of LaMnO3 nanoparticles.