A Study on Magnetic Properties of Rodlike β-FeOOH Nanoparticles and their Relation to the Magnetic Structure

The β-FeOOH nanoparticles are synthesized by a microemulsion with the nonionic surfactant, polyoxyethylene(4)nonyl-phenylether CH 3 (CH 2 ) 8 C 6 H 4 O(-CH 2 OCH 2 ) 4 H (NP-4). The product was characterized by IR, XRD, TEM, and the X-ray diffraction patterns are indexed. The results indicate that the β-FeOOH nanoparticles exhibit rodlike shape with 20-30nm length, and the crystal structure belongs to the monoclinic system with the lattice parameters a=0.9981nm, b=0.2948nm, c=1.0485 nm and β=92.26°. The β-FeOOH nanoparticles are modified by the surfactant. The modified β-FeOOH nanoparticles are paramagnetic at room temperature and may be antiferromagnetic or weakly ferrimagnetic at lower temperature. The 57 Fe Mossbauer spectra show that there is a transformation of the magnetic structure below 150K and there are two kinds of Fe-O octahedra in the lattice of the modified β-FeOOH nanoparticles. The numbers of the two kinds of Fe-O octahedra are not the same at room temperature and at low temperature.