**3. Results and discussion**

374 Advanced Aspects of Spectroscopy

oxide nanoparticles [20].

**2. Experiment** 

discussed as a function of the particle sizes.

6 h at various temperatures between 300 and 500°C.

nanoparticles are worthy to investigate.

from those of bulk ones. For instance, antiferromagnetic nanoparticles exhibit increasing net magnetization due to the presence of uncompensated surface spins [9, 10]. If the ferromagnetic behavior is promoted in LaFeO3, it should provide facile handling of their applications by using magnetic field. Magnetic properties of well-defined LaFeO3

It is well known that the wet-chemical methods offer large advantages for low-temperature oxide formation with high surface area, small particle size, and exact cation-stoichiometry. Several methods such as co-precipitation technique [11, 12], polymerized complex method [13], combustion synthesis [14], and sol-gel technique [15] were reported to prepare LaFeO3 nanoparticles. For instance the formation of a single phase of LaFeO3 with the perovskite structure was observed at lower calcination temperatures of 300°C in [11, 12]. This temperature was much lower than that of conventional solid state reaction method. Recently we have successfully prepared LaFeO3 nanoparticles by using the new chemical synthesis method, so-called "hot soap method" [16, 17]. It showed high controllability over the formation of nanoparticles with narrow size distribution, which was performed in the presence of surfactant molecules at high temperatures. The hot soap method is based on the thermal decomposition of reaction precursors of organometallic compounds in polyol solvent. But the presence of surfactant molecules in the solution prevents aggregation of precursors during growth. It was widely applied to prepare nanoparticles of compound semiconductors [18] and metallic alloys [19]. However there were few reports on preparing

In this paper we describe the details of our synthesis procedure of LaFeO3 nanoparticles by using the hot soap method. The magnetic properties of the resultant particles were also

LaFeO3 nanoparticles were synthesized by the hot soap method. Their synthesis procedure is outlined in Figure 1. All chemicals used in this experiment were of reagent grade and used without any further purification. Iron acetylacetonate (Fe(acac)3) and lanthanum acetate (La(ac)3·1.5H2O) were preferred as iron and lanthanum sources, respectively, that were soluble in organic solvents such as polyethylene glycol (PEG 400). In a typical synthesis procedure, equal amounts of Fe(acac)3 (1.2 mmol) and La(ac)3 (1.2 mmol) were weighed out accurately and charged into a reaction flask with 20 mL of PEG 400. Coordinating organic protective agents of oleic acid (5 mmol) and oleylamine (5 mmol) were injected into the reaction mixture and the transparent brown solution was observed. Thereafter, the mixture solution was raised to 200°C and maintained for 3 h with stirring. Before cooling down to room temperature, 50 mL of ethanol was added to the reaction mixture, in order to precipitate the particles. The precipitated particles were rinsed with ethanol and dried at 100°C for 1 h. Some of the sample powders were heat-treated in air for
