**2. Experiment**

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

Obtained sample powders were characterized by x-ray powder diffraction (XRD) with monochromatic Cu K radiation, infrared spectroscopy (IR), and thermogravimetry and differential thermal analysis (TG-DTA). Powder morphologies of the products were observed by scanning electron microscopy (SEM, Hitachi S-4300) at 20 kV and transmission electron microscopy (TEM, Topcon EM-002B) at 200 kV. The BET surface areas were measured by using N2 absorption at 77 K. The magnetic properties were investigated using a vibrating sample magnetometer with high-sensitivity SQUID sensor (MPMS SQUID-VSM) and conventional transmission Mössbauer spectroscopy with a 925 MBq 57Co/Rh source. The velocity scale of Mössbauer spectra was calibrated with reference to -Fe.

**Figure 1.** Flowchart of the procedure to prepare LaFeO3 nanoparticles.
