Combustion synthesis and characterization of nano‐crystalline LaFeO₃ powder

Abstract

Nano‐crystalline LaFeO3 was synthesized by a sol–gel auto‐combustion method from a mixed aqueous solution of lanthanum and iron nitride, using citric acid as the fuel. Powder X‐ray diffraction and TG/DTA analysis show that the LaFeO3 crystallites can be directly obtained by the sol–gel combustion process, without any other undesired phase. The results of SEM and TEM reveal that the as‐burnt samples and powder calcined at 700 °C are agglomerated with particle size in the range of 25–50 nm and 60–80 nm, respecitvely. The M (T) and M (H) curves measurements show the existence of a weak ferromagnetism and the mainly anti‐ferromagnetic ordering of the spins in the calcined sample. Compared with the powder calcined at 600 °C and 700 °C, the as‐burnt LaFeO3 exhibits much stronger ferromagnetic behavior, with larger magnetization and smaller coercive field. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Superparamagnetic Behaviour and Induced Ferrimagnetism of LaFeO3 Nanoparticles Prepared by a Hot-Soap Technique

“…This was mainly caused by antiferromagnetic ordering of the spins in the nanoparticles [27]. By the way, the sample prepared at 500°C showed the remarkable hysteresis gap than the other samples.…”

“…Only a slight canting of the adjacent Fe 3+ spins produced weak ferromagnetism. The spontaneous magnetization of LaFeO3 bulk crystals was only ~0.1 emu/g at room temperature [27]. However all samples seemed to have large magnetization, especially for the sample heat-treated at 350°C.…”

Lanthanum ferrite ferromagnetic nanocrystallites by a polymeric precursor route

“…However, low symmetry of the distorted orthorhombic perovskite-type structure leads to the tilt of FeO 6 octahedra. Consequently, a canted spin order is also formed in the Fe lattice, which gives rise to WFM along another crystallographic direction [59][60][61][62]. Therefore, both AFM and WFM ordering can be observed in the system, also influenced by the particle size and morphology.…”

“…Normally, the LaFeO 3 system is either weakly ferromagnetic (WFM) or antiferromagnetic (AFM) with a Néel temperature above 300 K [59]. For a 30 nm LaFeO 3 particle size system, different authors observed WFM, Qi et al [60] reported a coercive field of ∼90 Öe and a saturation magnetization M s of ∼2.75 emu/g at room temperature and Shen et al [61] reported a coercive field of 137 Öe and a spontaneous magnetization about 0.10 emu/g, while Sivakumar et al [62] reported values of ∼250 Öe and ∼0.04 emu/g, attributed to the increase in the magneto-crystalline anisotropy with the decrease in particle size in nanosized crystallites. Qi et al [60] observed that the AFM interaction becomes dominant when LaFeO 3 nanocrystallites obtained by the sol-gel autocombustion method are calcined, while WFM is observed for non-calcined LaFeO 3 powder.…”

“…Based on the target applications, different synthesis methods have been used as alternative for solid state reactions and mechanical chemical solid reaction, including coprecipitation [21,22], combustion [23][24][25][26], sol-gel [27][28][29], gel [30] and sol-gel [31], autocombustion, polyol [32], microemulsion [33], hydrothermal [34], sonochemical [35], low temperature [36] and microwave assisted [37] thermal decomposition. However there are no studies concerning the presence of residual carbon, the calcination temperature that should be used to eliminate it, or the thermal evolution of the obtained powders: crystal size, presence of agglomerates.…”