Preparation, characterization, magnetic property, and Mössbauer spectra of the β-FeOOH nanoparticles modified by nonionic surfactant

β-FeOOH nanoparticles have been prepared in a microemulsion system with nonionic surfactant polyoxyethylene(4)nonylphenylether CH3(CH2)8C6H4O(CH2OCH2)4H. The powder X-ray diffraction, infrared spectra, and transmission electron microscopic images indicate that the products are 20–30 nm length nanorods with a crystal structure belonging to monoclinic β-FeOOH and lattice parameters of a=0.9981, b=0.2948, c=1.0485 nm and β=92.26°. The size and shapes of β-FeOOH nanoparticles can be manipulated by the surfactant. The modified β-FeOOH nanoparticles are paramagnetic at room temperature and may be antiferromagnetic or weakly ferrimagnetic at lower temperatures. The 57Fe Mössbauer spectra show that the magnetic structure transforms below 150 K and two kinds of Fe–O octahedra exist in the lattice of the modified β-FeOOH nanoparticles. The numbers of each kind of Fe–O octahedra are not the same at room temperature or at low temperatures.